Academic Appointments

Administrative Appointments

  • Director, Stanford Center for Population Research (2010 - 2015)
  • Director, Demography Core, Center for Demography and Economics of Health and Aging (2009 - 2014)

Current Research and Scholarly Interests

Shripad Tuljapurkar is Professor of Biology and the Dean & Virginia Morrison Professor of Population Studies at Stanford University. His research areas include stochastic dynamics of human and natural populations; life history evolution, especially senescence; prehistoric societies; and probability forecasts including sex ratios, mortality, aging and fiscal balance.

Tuljapurkar directs Stanford’s Center for Population Research and the demography program at Stanford’s Center for the Demography and Economics of Health and Aging. He is a member of the Center for the Demography and Economics of Aging at the University of California, Berkeley. He has led a panel on aging for the International Union for the Scientific Study of Population and served on the Technical Advisory Panel to the US Social Security Administration. He received the 1996 Mindel Sheps Award from the Population Association of America, and a John Simon Guggenheim Fellowship in 1998.

Stanford Advisees

Graduate and Fellowship Programs

  • Biology (School of Humanities and Sciences) (Phd Program)

All Publications

  • Advancing methods for the biodemography of aging within social contexts. Neuroscience and biobehavioral reviews Hernandez-Pacheco, R., Steiner, U. K., Rosati, A. G., Tuljapurkar, S. 2023: 105400


    Several social dimensions including social integration, status, early-life adversity, and their interactions across the life course can predict health, reproduction, and mortality in humans. Accordingly, the social environment plays a fundamental role in the emergence of phenotypes driving the evolution of aging. Recent work placing human social gradients on a biological continuum with other species provides a useful evolutionary context for aging questions, but there is still a need for a unified evolutionary framework linking health and aging within social contexts. Here, we summarize current challenges to understand the role of the social environment in human life courses. Next, we review recent advances in comparative biodemography and propose a biodemographic perspective to address socially driven health phenotype distributions and their evolutionary consequences using a nonhuman primate population. This new comparative approach uses evolutionary demography to address the joint dynamics of populations, social dimensions, phenotypes, and life history parameters. The long-term goal is to advance our understanding of the link between individual social environments, population-level outcomes, and the evolution of aging.

    View details for DOI 10.1016/j.neubiorev.2023.105400

    View details for PubMedID 37739326

  • How the demographic transition affects kinship networks: A formal demographic approach DEMOGRAPHIC RESEARCH Jiang, S., Zuo, W., Guo, Z., Caswell, H., Tuljapurkar, S. 2023; 48: 899-930
  • Hurricanes affect diversification among individual life courses of a primate population. The Journal of animal ecology Diaz, A. A., Steiner, U. K., Tuljapurkar, S., Zuo, W., Hernández-Pacheco, R. 2023


    Extreme climatic events may influence individual-level variability in phenotypes, survival and reproduction, and thereby drive the pace of evolution. Climate models predict increases in the frequency of intense hurricanes, but no study has measured their impact on individual life courses within animal populations. We used 45 years of demographic data of rhesus macaques to quantify the influence of major hurricanes on reproductive life courses using multiple metrics of dynamic heterogeneity accounting for life course variability and life-history trait variances. To reduce intraspecific competition, individuals may explore new reproductive stages during years of major hurricanes, resulting in higher temporal variation in reproductive trajectories. Alternatively, individuals may opt for a single optimal life-history strategy due to trade-offs between survival and reproduction. Our results show that heterogeneity in reproductive life courses increased by 4% during years of major hurricanes, despite a 2% reduction in the asymptotic growth rate due to an average decrease in mean fertility and survival by that is, shortened life courses and reduced reproductive output. In agreement with this, the population is expected to achieve stable population dynamics faster after being perturbed by a hurricane ( ρ = 1.512 $$ \rho =1.512 $$ ; 95% CI: 1.488, 1.538), relative to ordinary years ρ = 1.482 ; 1.475 , 1.490 $$ \left(\rho =1.482;1.475,1.490\right) $$ . Our work suggests that natural disasters force individuals into new demographic roles to potentially reduce competition during unfavourable environments where mean reproduction and survival are compromised. Variance in lifetime reproductive success and longevity are differently affected by hurricanes, and such variability is mostly driven by survival.

    View details for DOI 10.1111/1365-2656.13942

    View details for PubMedID 37190852

  • Why life expectancy over-predicts crude death rate GENUS Liang, H., Guo, Z., Tuljapurkar, S. 2023; 79 (1)
  • Adaption, neutrality and life-course diversity. Ecology letters Steiner, U. K., Tuljapurkar, S. 2023


    Heterogeneity among individuals in fitness components is what selection acts upon. Evolutionary theories predict that selection in constant environments acts against such heterogeneity. But observations reveal substantial non-genetic and also non-environmental variability in phenotypes. Here, we examine whether there is a relationship between selection pressure and phenotypic variability by analysing structured population models based on data from a large and diverse set of species. Our findings suggest that non-genetic, non-environmental variation is in general neither truly neutral, selected for, nor selected against. We find much variations among species and populations within species, with mean patterns suggesting nearly neutral evolution of life-course variability. Populations that show greater diversity of life courses do not show, in general, increased or decreased population growth rates. Our analysis suggests we are only at the beginning of understanding the evolution and maintenance of non-genetic non-environmental variation.

    View details for DOI 10.1111/ele.14174

    View details for PubMedID 36756864

  • Reproductive dispersion and damping time scale with life-history speed. Ecology letters Jiang, S., Jaggi, H., Zuo, W., Oli, M. K., Coulson, T., Gaillard, J. M., Tuljapurkar, S. 2022


    Iteroparous species may reproduce at many different ages, resulting in a reproductive dispersion that affects the damping of population perturbations, and varies among life histories. Since generation time ( T c $$ {T}_c $$ ) is known to capture aspects of life-history variation, such as life-history speed, does T c $$ {T}_c $$ also determine reproductive dispersion ( S $$ S $$ ) or damping time ( τ $$ \tau $$ )? Using phylogenetically corrected analyses on 633 species of animals and plants, we find, firstly, that reproductive dispersion S $$ S $$ scales isometrically with T c $$ {T}_c $$ . Secondly, and unexpectedly, we find that the damping time ( τ $$ \tau $$ ) does not scale isometrically with generation time, but instead changes only as T c b $$ {T}_c^b $$ with b < 1 $$ b<1 $$ (also, there is a similar scaling with S $$ S $$ ). This non-isometric scaling implies a novel demographic contrast: increasing generation times correspond to a proportional increase in reproductive dispersion, but only to a slower increase in the damping time. Thus, damping times are partly decoupled from the slow-fast continuum, and are determined by factors other than allometric constraints.

    View details for DOI 10.1111/ele.14080

    View details for PubMedID 35925997

  • Mutations and the Distribution of Lifetime Reproductive Success JOURNAL OF THE INDIAN INSTITUTE OF SCIENCE Tuljapurkar, S., Zuo, W. 2022
  • Quantifying the effect of genetic, environmental and individual demographic stochastic variability for population dynamics in Plantago lanceolata. Scientific reports Steiner, U. K., Tuljapurkar, S., Roach, D. A. 2021; 11 (1): 23174


    Simple demographic events, the survival and reproduction of individuals, drive population dynamics. These demographic events are influenced by genetic and environmental parameters, and are the focus of many evolutionary and ecological investigations that aim to predict and understand population change. However, such a focus often neglects the stochastic events that individuals experience throughout their lives. These stochastic events also influence survival and reproduction and thereby evolutionary and ecological dynamics. Here, we illustrate the influence of such non-selective demographic variability on population dynamics using population projection models of an experimental population of Plantago lanceolata. Our analysis shows that the variability in survival and reproduction among individuals is largely due to demographic stochastic variation with only modest effects of differences in environment, genes, and their interaction. Common expectations of population growth, based on expected lifetime reproduction and generation time, can be misleading when demographic stochastic variation is large. Large demographic stochastic variation exhibited within genotypes can lower population growth and slow evolutionary adaptive dynamics. Our results accompany recent investigations that call for more focus on stochastic variation in fitness components, such as survival, reproduction, and functional traits, rather than dismissal of this variation as uninformative noise.

    View details for DOI 10.1038/s41598-021-02468-9

    View details for PubMedID 34848768

  • Demographic determinants of the phenotypic mother-offspring correlation ECOLOGICAL MONOGRAPHS Plard, F., Barthold Jones, J. A., Gaillard, J., Coulson, T., Tuljapurkar, S. 2021

    View details for DOI 10.1002/ecm.1479

    View details for Web of Science ID 000695317100001

  • Skewed distributions of lifetime reproductive success: beyond mean and variance. Ecology letters Tuljapurkar, S., Zuo, W., Coulson, T., Horvitz, C., Gaillard, J. 2020


    Lifetime reproductive performance is quantified here by the LRS (lifetime reproductive success), the random number of offspring an individual produces over its lifetime. Many field studies find that distributions of LRS among individuals are non-normal, zero-inflated and highly skewed. These results beg the question, what is the distribution of LRS predicted by demographic models when the only source of randomness is demographic stochasticity? Here we present the first exact analysis of the probability distribution of LRS for species described by age+stage models; our analysis starts with estimated vital rates. We illustrate with three examples: the Hadza, human hunter-foragers (age-only), the evergreen tree Tsuga canadensis (stage-only) and Roe deer, Capreolus capreolus (age+stage). For each we obtain the exact distribution of LRS, but also calculate and discuss the first three moments. Our results point to important questions about how such LRS distributions affect natural selection, and life history evolution.

    View details for DOI 10.1111/ele.13467

    View details for PubMedID 32043827

  • How climate affects extreme events and hence ecological population models ECOLOGY Rypkema, D. C., Horvitz, C. C., Tuljapurkar, S. 2019; 100 (6)

    View details for DOI 10.1002/ecy.2684

    View details for Web of Science ID 000474127300023

  • How climate affects extreme events and hence ecological population models. Ecology Rypkema, D. C., Horvitz, C. C., Tuljapurkar, S. 2019: e02684


    Extreme events significantly impact ecosystems and are predicted to increase in frequency and/or magnitude with climate change. Generalized extreme value (GEV) distributions describe most ecologically-relevant extreme events, including hurricanes, wildfires, exotic species outbreaks, and disease spread. In climate science, the GEV is widely used as an accurate and flexible tool over large spatial scales (>> 105 km2 ) to study how changes in climate shift extreme events. However, ecologists rarely use the GEV to study how climate change affects populations. Here we show how to estimate a GEV for hurricanes at an ecologically-relevant (< 103 km2 ) spatial scale, and use the results in a stochastic, empirically-based matrix population model. As a case study, we use an understory shrub in southeast Florida with hurricane-driven dynamics and measure the effects of change using the stochastic population growth rate. We use sensitivities to analyze how population growth rate is affected by changes in hurricane frequency and intensity, canopy damage levels, and canopy recovery rates. Our results emphasize the importance of accurately estimating location-specific storm frequency. In a rapidly changing world, our methods show how to combine realistic extreme event and population models to assess ecological impacts and to prioritize conservation actions for at-risk populations. This article is protected by copyright. All rights reserved.

    View details for PubMedID 30847905

  • Advancing front of old-age human survival. Proceedings of the National Academy of Sciences of the United States of America Zuo, W., Jiang, S., Guo, Z., Feldman, M. W., Tuljapurkar, S. 2018; 115 (44): 11209–14


    Old-age mortality decline has driven recent increases in lifespans, but there is no agreement about trends in the age pattern of old-age deaths. Some argue that old-age deaths should become compressed at advanced ages, others argue that old-age deaths should become more dispersed with age, and yet others argue that old-age deaths are consistent with little change in dispersion. However, direct analysis of old-age deaths presents unusual challenges: Death rates at the oldest ages are always noisy, published life tables must assume an asymptotic age pattern of deaths, and the definition of "old-age" changes as lives lengthen. Here we use robust percentile-based methods to overcome some of these challenges and show, for five decades in 20 developed countries, that old-age survival follows an advancing front, like a traveling wave. The front lies between the 25th and 90th percentiles of old-age deaths, advancing with nearly constant long-term shape but annual fluctuations in speed. The existence of this front leads to several predictions that we verify, e.g., that advances in life expectancy at age 65 y are highly correlated with the advance of the 25th percentile, but not with distances between higher percentiles. Our unexpected result has implications for biological hypotheses about human aging and for future mortality change.

    View details for PubMedID 30327342

  • The big challenges in modeling human and environmental well-being. F1000Research Tuljapurkar, S. 2016; 5


    This article is a selective review of quantitative research, historical and prospective, that is needed to inform sustainable development policy. I start with a simple framework to highlight how demography and productivity shape human well-being. I use that to discuss three sets of issues and corresponding challenges to modeling: first, population prehistory and early human development and their implications for the future; second, the multiple distinct dimensions of human and environmental well-being and the meaning of sustainability; and, third, inequality as a phenomenon triggered by development and models to examine changing inequality and its consequences. I conclude with a few words about other important factors: political, institutional, and cultural.

    View details for DOI 10.12688/f1000research.7636.1

    View details for PubMedID 27134734

    View details for PubMedCentralID PMC4833055

  • Limitations of GCTA as a solution to the missing heritability problem PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Kumar, S. K., Feldman, M. W., Rehkopf, D. H., Tuljapurkar, S. 2016; 113 (1): E61-E70


    Genome-wide association studies (GWASs) seek to understand the relationship between complex phenotype(s) (e.g., height) and up to millions of single-nucleotide polymorphisms (SNPs). Early analyses of GWASs are commonly believed to have "missed" much of the additive genetic variance estimated from correlations between relatives. A more recent method, genome-wide complex trait analysis (GCTA), obtains much higher estimates of heritability using a model of random SNP effects correlated between genotypically similar individuals. GCTA has now been applied to many phenotypes from schizophrenia to scholastic achievement. However, recent studies question GCTA's estimates of heritability. Here, we show that GCTA applied to current SNP data cannot produce reliable or stable estimates of heritability. We show first that GCTA depends sensitively on all singular values of a high-dimensional genetic relatedness matrix (GRM). When the assumptions in GCTA are satisfied exactly, we show that the heritability estimates produced by GCTA will be biased and the standard errors will likely be inaccurate. When the population is stratified, we find that GRMs typically have highly skewed singular values, and we prove that the many small singular values cannot be estimated reliably. Hence, GWAS data are necessarily overfit by GCTA which, as a result, produces high estimates of heritability. We also show that GCTA's heritability estimates are sensitive to the chosen sample and to measurement errors in the phenotype. We illustrate our results using the Framingham dataset. Our analysis suggests that results obtained using GCTA, and the results' qualitative interpretations, should be interpreted with great caution.

    View details for DOI 10.1073/pnas.1520109113

    View details for Web of Science ID 000367520400011

    View details for PubMedCentralID PMC4711841

  • Deciphering life history transcriptomes in different environments MOLECULAR ECOLOGY Etges, W. J., Trotter, M. V., de Oliveira, C. C., Rajpurohit, S., Gibbs, A. G., Tuljapurkar, S. 2015; 24 (1): 151-179


    We compared whole transcriptome variation in six pre-adult stages and seven adult female ages in two populations of cactophilic Drosophila mojavensis reared on two host plants to understand how differences in gene expression influence standing life history variation. We used singular value decomposition (SVD) to identify dominant trajectories of life cycle gene expression variation, performed pairwise comparisons of stage and age differences in gene expression across the life cycle, identified when genes exhibited maximum levels of life cycle gene expression, and assessed population and host cactus effects on gene expression. Life cycle SVD analysis returned four significant components of transcriptional variation, revealing functional enrichment of genes responsible for growth, metabolic function, sensory perception, neural function, translation and ageing. Host cactus effects on female gene expression revealed population- and stage-specific differences, including significant host plant effects on larval metabolism and development, as well as adult neurotransmitter binding and courtship behaviour gene expression levels. In 3- to 6-day-old virgin females, significant upregulation of genes associated with meiosis and oogenesis was accompanied by downregulation of genes associated with somatic maintenance, evidence for a life history trade-off. The transcriptome of D. mojavensis reared in natural environments throughout its life cycle revealed core developmental transitions and genome-wide influences on life history variation in natural populations.

    View details for DOI 10.1111/mec.13017

    View details for Web of Science ID 000347446300012

    View details for PubMedID 25442828

  • Generation time, net reproductive rate, and growth in stage-age-structured populations. American naturalist Steiner, U. K., Tuljapurkar, S., Coulson, T. 2014; 183 (6): 771-783


    Abstract Major insights into the relationship between life-history features and fitness have come from Lotka's proof that population growth rate is determined by the level (expected amount) of reproduction and the average timing of reproduction of an individual. But this classical result is limited to age-structured populations. Here we generalize this result to populations structured by stage and age by providing a new, unique measure of reproductive timing (Tc) that, along with net reproductive rate (R0), has a direct mathematical relationship to and approximates growth rate (r). We use simple examples to show how reproductive timing Tc and level R0 are shaped by stage dynamics (individual trait changes), selection on the trait, and parent-offspring phenotypic correlation. We also show how population structure can affect dispersion in reproduction among ages and stages. These macroscopic features of the life history determine population growth rate r and reveal a complex interplay of trait dynamics, timing, and level of reproduction. Our results contribute to a new framework of population and evolutionary dynamics in stage-and-age-structured populations.

    View details for DOI 10.1086/675894

    View details for PubMedID 24823821

  • Divergence in age patterns of mortality change drives international divergence in lifespan inequality. Demography Gillespie, D. O., Trotter, M. V., Tuljapurkar, S. D. 2014; 51 (3): 1003-1017


    In the past six decades, lifespan inequality has varied greatly within and among countries even while life expectancy has continued to increase. How and why does mortality change generate this diversity? We derive a precise link between changes in age-specific mortality and lifespan inequality, measured as the variance of age at death. Key to this relationship is a young-old threshold age, below and above which mortality decline respectively decreases and increases lifespan inequality. First, we show for Sweden that shifts in the threshold's location have modified the correlation between changes in life expectancy and lifespan inequality over the last two centuries. Second, we analyze the post-World War II (WWII) trajectories of lifespan inequality in a set of developed countries-Japan, Canada, and the United States-where thresholds centered on retirement age. Our method reveals how divergence in the age pattern of mortality change drives international divergence in lifespan inequality. Most strikingly, early in the 1980s, mortality increases in young U.S. males led to a continuation of high lifespan inequality in the United States; in Canada, however, the decline of inequality continued. In general, our wider international comparisons show that mortality change varied most at young working ages after WWII, particularly for males. We conclude that if mortality continues to stagnate at young ages yet declines steadily at old ages, increases in lifespan inequality will become a common feature of future demographic change.

    View details for DOI 10.1007/s13524-014-0287-8

    View details for PubMedID 24756909

    View details for PubMedCentralID PMC4067902

  • Neutral theory for life histories and individual variability in fitness components PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Steiner, U. K., Tuljapurkar, S. 2012; 109 (12): 4684-4689


    Individuals within populations can differ substantially in their life span and their lifetime reproductive success but such realized individual variation in fitness components need not reflect underlying heritable fitness differences visible to natural selection. Even so, biologists commonly argue that large differences in fitness components are likely adaptive, resulting from and driving evolution by natural selection. To examine this argument we use unique formulas to compute exactly the variance in life span and in lifetime reproductive success among individuals with identical (genotypic) vital rates (assuming a common genotype for all individuals). Such individuals have identical fitness but vary substantially in their realized individual fitness components. We show by example that our computed variances and corresponding simulated distribution of fitness components match those observed in real populations. Of course, (genotypic) vital rates in real populations are expected to differ by small but evolutionarily important amounts among genotypes, but we show that such differences only modestly increase variances in fitness components. We conclude that observed differences in fitness components may likely be evolutionarily neutral, at least to the extent that they are indistinguishable from distributions generated by neutral processes. Important consequences of large neutral variation are the following: Heritabilities for fitness components are likely to be small (which is in fact the case), small selective differences in life histories will be hard to measure, and the effects of random drift will be amplified in natural populations by the large variances among individuals.

    View details for DOI 10.1073/pnas.1018096109

    View details for Web of Science ID 000301712600067

    View details for PubMedID 22392997

    View details for PubMedCentralID PMC3311353

  • Inequality in life spans and a new perspective on mortality convergence across industrialized countries POPULATION AND DEVELOPMENT REVIEW Edwards, R. D., Tuljapurkar, S. 2005; 31 (4): 645-?
  • Gompertz law revisited: Forecasting mortality with a multi-factor exponential model INSURANCE MATHEMATICS & ECONOMICS Li, H., Tan, K., Tuljapurkar, S., Zhu, W. 2021; 99: 268-281
  • Distributions of LRS in varying environments. Ecology letters Tuljapurkar, S., Zuo, W., Coulson, T., Horvitz, C., Gaillard, J. 2021


    The lifetime reproductive success (LRS) of individuals is affected by random events such as death, realized growth or realized reproduction, and the outcomes of these events can differ even when individuals have identical probabilities. Another source of randomness arises when these probabilities also change over time in variable environments. For structured populations in stochastic environments, we extend our recent method to determine how birth environment and birth stage determine the random distribution of the LRS. Our results provide a null model that quantifies effects on LRS of just the birth size or stage. Using Roe deer Capreolus capreolus as a case study, we show that the effect of an individual's birth environment on LRS varies with the frequency of environments and their temporal autocorrelation, and that lifetime performance is affected by changes in the pattern of environmental states expected as a result of climate change.

    View details for DOI 10.1111/ele.13745

    View details for PubMedID 33904254

  • Relative contributions of fixed and dynamic heterogeneity to variation in lifetime reproductive success in kestrels (Falco tinnunculus) POPULATION ECOLOGY Broekman, M. E., Jongejans, E., Tuljapurkar, S. 2020
  • Drivers of diversity in individual life courses: Sensitivity of the population entropy of a Markov chain. Theoretical population biology Steiner, U. K., Tuljapurkar, S. n. 2020


    Individuals differ in their life courses, but how this diversity is generated, how it has evolved and how it is maintained is less understood. However, this understanding is crucial to comprehend evolutionary and ecological population dynamics. In structured populations, individual life courses represent sequences of stages that end in death. These life course trajectories or sequences can be described by a Markov chain and individuals diversify over the course of their lives by transitioning through diverse discrete stages. The rate at which stage sequences diversify with age can be quantified by the population entropy of a Markov chain. Here, we derive sensitivities of the population entropy of a Markov chain to identify which stage transitions generate-or contribute-most to diversification in stage sequences, i.e. life courses. We then use these sensitivities to reveal potential selective forces on the dynamics of life courses. To do so we correlated the sensitivity of each matrix element (stage transition) with respect to the population entropy, to its sensitivity with respect to fitness λ, the population growth rate. Positive correlation between the two sensitivities would suggest that the stage transitions that selection has acted most strongly on (high sensitivities with respect to λ) are also those that contributed most to the diversification of life courses. Using an illustrative example on a seabird population, the Thick-billed Murres on Coats Island, that is structured by reproductive stages, we show that the most influential stage transitions for diversification of life courses are not correlated with the most influential transitions for population growth. Our finding suggests that observed diversification in life courses is neutral rather than adaptive, note this does not imply that the life histories themselves are not adaptive. We are at an early stage of understanding how individual level dynamics shape ecological and evolutionary dynamics, and many discoveries await.

    View details for DOI 10.1016/j.tpb.2020.01.003

    View details for PubMedID 31958474

  • Life-history strategy varies with the strength of competition in a food-limited ungulate population. Ecology letters Kentie, R. n., Clegg, S. M., Tuljapurkar, S. n., Gaillard, J. M., Coulson, T. n. 2020


    Fluctuating population density in stochastic environments can contribute to maintain life-history variation within populations via density-dependent selection. We used individual-based data from a population of Soay sheep to examine variation in life-history strategies at high and low population density. We incorporated life-history trade-offs among survival, reproduction and body mass growth into structured population models and found support for the prediction that different life-history strategies are optimal at low and high population densities. Shorter generation times and lower asymptotic body mass were selected for in high-density environments even though heavier individuals had higher probabilities to survive and reproduce. In contrast, greater asymptotic body mass and longer generation times were optimal at low population density. If populations fluctuate between high density when resources are scarce, and low densities when they are abundant, the variation in density will generate fluctuating selection for different life-history strategies, that could act to maintain life-history variation.

    View details for DOI 10.1111/ele.13470

    View details for PubMedID 32090452

  • Climate, rather than human disturbance, is the main driver of age-specific mortality trajectories in a tropical tree ECOLOGICAL MODELLING Gaoue, O. G., Horvitz, C. C., Steiner, U. K., Tuljapurkar, S. 2019; 400: 34–40
  • Age distribution, trends, and forecasts of under-5 mortality in 31 sub-Saharan African countries: A modeling study. PLoS medicine Mejía-Guevara, I., Zuo, W., Bendavid, E., Li, N., Tuljapurkar, S. 2019; 16 (3): e1002757


    Despite the sharp decline in global under-5 deaths since 1990, uneven progress has been achieved across and within countries. In sub-Saharan Africa (SSA), the Millennium Development Goals (MDGs) for child mortality were met only by a few countries. Valid concerns exist as to whether the region would meet new Sustainable Development Goals (SDGs) for under-5 mortality. We therefore examine further sources of variation by assessing age patterns, trends, and forecasts of mortality rates.Data came from 106 nationally representative Demographic and Health Surveys (DHSs) with full birth histories from 31 SSA countries from 1990 to 2017 (a total of 524 country-years of data). We assessed the distribution of age at death through the following new demographic analyses. First, we used a direct method and full birth histories to estimate under-5 mortality rates (U5MRs) on a monthly basis. Second, we smoothed raw estimates of death rates by age and time by using a two-dimensional P-Spline approach. Third, a variant of the Lee-Carter (LC) model, designed for populations with limited data, was used to fit and forecast age profiles of mortality. We used mortality estimates from the United Nations Inter-agency Group for Child Mortality Estimation (UN IGME) to adjust, validate, and minimize the risk of bias in survival, truncation, and recall in mortality estimation. Our mortality model revealed substantive declines of death rates at every age in most countries but with notable differences in the age patterns over time. U5MRs declined from 3.3% (annual rate of reduction [ARR] 0.1%) in Lesotho to 76.4% (ARR 5.2%) in Malawi, and the pace of decline was faster on average (ARR 3.2%) than that observed for infant (IMRs) (ARR 2.7%) and neonatal (NMRs) (ARR 2.0%) mortality rates. We predict that 5 countries (Kenya, Rwanda, Senegal, Tanzania, and Uganda) are on track to achieve the under-5 sustainable development target by 2030 (25 deaths per 1,000 live births), but only Rwanda and Tanzania would meet both the neonatal (12 deaths per 1,000 live births) and under-5 targets simultaneously. Our predicted NMRs and U5MRs were in line with those estimated by the UN IGME by 2030 and 2050 (they overlapped in 27/31 countries for NMRs and 22 for U5MRs) and by the Institute for Health Metrics and Evaluation (IHME) by 2030 (26/31 and 23/31, respectively). This study has a number of limitations, including poor data quality issues that reflected bias in the report of births and deaths, preventing reliable estimates and predictions from a few countries.To our knowledge, this study is the first to combine full birth histories and mortality estimates from external reliable sources to model age patterns of under-5 mortality across time in SSA. We demonstrate that countries with a rapid pace of mortality reduction (ARR ≥ 3.2%) across ages would be more likely to achieve the SDG mortality targets. However, the lower pace of neonatal mortality reduction would prevent most countries from achieving those targets: 2 countries would reach them by 2030, 13 between 2030 and 2050, and 13 after 2050.

    View details for DOI 10.1371/journal.pmed.1002757

    View details for PubMedID 30861006

    View details for PubMedCentralID PMC6413894

  • Age distribution, trends, and forecasts of under-5 mortality in 31 sub-Saharan African countries: A modeling study PLoS Medicine Mejía-Guevara, I., Zuo, W., Bendavid, E., Li, N., Tuljapurkar, S. 2019; 16 (3): 1-21
  • Susceptibility of wild and colonized Anopheles stephensi to Plasmodium vivax infection MALARIA JOURNAL Mohanty, A., Nina, P., Ballav, S., Vernekar, S., Parkar, S., D'souza, M., Zuo, W., Gomes, E., Chery, L., Tuljapurkar, S., Valecha, N., Rathod, P. K., Kumar, A. 2018; 17: 225


    As much as 80% of global Plasmodium vivax infections occur in South Asia and there is a shortage of direct studies on infectivity of P. vivax in Anopheles stephensi, the most common urban mosquito carrying human malaria. In this quest, the possible effects of laboratory colonization of mosquitoes on infectivity and development of P. vivax is of interest given that colonized mosquitoes can be genetically less divergent than the field population from which they originated.Patient-derived P. vivax infected blood was fed to age-matched wild and colonized An. stephensi. Such a comparison requires coordinated availability of same-age wild and colonized mosquito populations. Here, P. vivax infection are studied in colonized An. stephensi in their 66th-86th generation and fresh field-caught An. stephensi. Wild mosquitoes were caught as larvae and pupae and allowed to develop into adult mosquitoes in the insectary. Parasite development to oocyst and sporozoite stages were assessed on days 7/8 and 12/13, respectively.While there were batch to batch variations in infectivity of individual patient-derived P. vivax samples, both wild and colonized An. stephensi were roughly equally susceptible to oocyst stage Plasmodium infection. At the level of sporozoite development, significantly more mosquitoes with sporozoite load of 4+ were seen in wild than in colonized populations.

    View details for PubMedID 29871629

  • Poverty dynamics, poverty thresholds and mortality: An age-stage Markovian model PLOS ONE Bernstein, S., Rehkopf, D., Tuljapurkar, S., Horvitz, C. C. 2018; 13 (5): e0195734


    Recent studies have examined the risk of poverty throughout the life course, but few have considered how transitioning in and out of poverty shape the dynamic heterogeneity and mortality disparities of a cohort at each age. Here we use state-by-age modeling to capture individual heterogeneity in crossing one of three different poverty thresholds (defined as 1×, 2× or 3× the "official" poverty threshold) at each age. We examine age-specific state structure, the remaining life expectancy, its variance, and cohort simulations for those above and below each threshold. Survival and transitioning probabilities are statistically estimated by regression analyses of data from the Health and Retirement Survey RAND data-set, and the National Longitudinal Survey of Youth. Using the results of these regression analyses, we parameterize discrete state, discrete age matrix models. We found that individuals above all three thresholds have higher annual survival than those in poverty, especially for mid-ages to about age 80. The advantage is greatest when we classify individuals based on 1× the "official" poverty threshold. The greatest discrepancy in average remaining life expectancy and its variance between those above and in poverty occurs at mid-ages for all three thresholds. And fewer individuals are in poverty between ages 40-60 for all three thresholds. Our findings are consistent with results based on other data sets, but also suggest that dynamic heterogeneity in poverty and the transience of the poverty state is associated with income-related mortality disparities (less transience, especially of those above poverty, more disparities). This paper applies the approach of age-by-stage matrix models to human demography and individual poverty dynamics. In so doing we extend the literature on individual poverty dynamics across the life course.

    View details for PubMedID 29768416

  • Machine learning approaches to the social determinants of health in the health and retirement study SSM-POPULATION HEALTH Seligman, B., Tuljapurkar, S., Rehkopf, D. 2018; 4: 95–99


    Social and economic factors are important predictors of health and of recognized importance for health systems. However, machine learning, used elsewhere in the biomedical literature, has not been extensively applied to study relationships between society and health. We investigate how machine learning may add to our understanding of social determinants of health using data from the Health and Retirement Study.A linear regression of age and gender, and a parsimonious theory-based regression additionally incorporating income, wealth, and education, were used to predict systolic blood pressure, body mass index, waist circumference, and telomere length. Prediction, fit, and interpretability were compared across four machine learning methods: linear regression, penalized regressions, random forests, and neural networks.All models had poor out-of-sample prediction. Most machine learning models performed similarly to the simpler models. However, neural networks greatly outperformed the three other methods. Neural networks also had good fit to the data (R 2 between 0.4-0.6, versus <0.3 for all others). Across machine learning models, nine variables were frequently selected or highly weighted as predictors: dental visits, current smoking, self-rated health, serial-seven subtractions, probability of receiving an inheritance, probability of leaving an inheritance of at least $10,000, number of children ever born, African-American race, and gender.Some of the machine learning methods do not improve prediction or fit beyond simpler models, however, neural networks performed well. The predictors identified across models suggest underlying social factors that are important predictors of biological indicators of chronic disease, and that the non-linear and interactive relationships between variables fundamental to the neural network approach may be important to consider.

    View details for PubMedID 29349278

  • Demographic and clinical profiles of Plasmodium falciparum and Plasmodium vivax patients at a tertiary care centre in southwestern India MALARIA JOURNAL Chery, L., Maki, J. N., Mascarenhas, A., Walke, J. T., Gawas, P., Almeida, A., Fernandes, M., Vaz, M., Ramanan, R., Shirodkar, D., Bernabeu, M., Manoharan, S. K., Pereira, L., Dash, R., Sharma, A., Shaik, R. B., Chakrabarti, R., Babar, P., White, J., Mudeppa, D. G., Kumar, S., Zuo, W., Skillman, K. M., Kanjee, U., Lim, C., Shaw-Saliba, K., Kumar, A., Valecha, N., Jindal, V. N., Khandeparkar, A., Naik, P., Amonkar, S., Duraisingh, M. T., Tuljapurkar, S., Smith, J. D., Dubhashi, N., Pinto, R. G., Silveria, M., Gomes, E., Rathod, P. K. 2016; 15


    Malaria remains an important cause of morbidity and mortality in India. Though many comprehensive studies have been carried out in Africa and Southeast Asia to characterize and examine determinants of Plasmodium falciparum and Plasmodium vivax malaria pathogenesis, fewer have been conducted in India.A prospective study of malaria-positive individuals was conducted at Goa Medical College and Hospital (GMC) from 2012 to 2015 to identify demographic, diagnostic and clinical indicators associated with P. falciparum and P. vivax infection on univariate analysis.Between 2012 and 2015, 74,571 febrile individuals, 6287 (8.4%) of whom were malaria positive, presented to GMC. The total number of malaria cases at GMC increased more than two-fold over four years, with both P. vivax and P. falciparum cases present year-round. Some 1116 malaria-positive individuals (mean age = 27, 91% male), 88.2% of whom were born outside of Goa and 51% of whom were construction workers, were enroled in the study. Of 1088 confirmed malaria-positive patients, 77.0% had P. vivax, 21.0% had P. falciparum and 2.0% had mixed malaria. Patients over 40 years of age and with P. falciparum infection were significantly (p < 0.001) more likely to be hospitalised than younger and P. vivax patients, respectively. While approximately equal percentages of hospitalised P. falciparum (76.6%) and P. vivax (78.9%) cases presented with at least one WHO severity indicator, a greater percentage of P. falciparum inpatients presented with at least two (43.9%, p < 0.05) and at least three (29.9%, p < 0.01) severity features. There were six deaths among the 182 hospitalised malaria positive patients, all of whom had P. falciparum.During the four year study period at GMC, the number of malaria cases increased substantially and the greatest burden of severe disease was contributed by P. falciparum.

    View details for DOI 10.1186/s12936-016-1619-5

    View details for Web of Science ID 000388529700001

    View details for PubMedID 27884146

    View details for PubMedCentralID PMC5123287

  • Racial and Socioeconomic Variation in Genetic Markers of Telomere Length: A Cross-Sectional Study of U.S. Older Adults. EBioMedicine Hamad, R., Tuljapurkar, S., Rehkopf, D. H. 2016; 11: 296-301


    Shorter telomere length (TL) has been associated with stress and adverse socioeconomic conditions, yet U.S. blacks have longer TL than whites. The role of genetic versus environmental factors in explaining TL by race and socioeconomic position (SEP) remains unclear.We used data from the U.S. Health and Retirement Study (N=11,934) to test the hypothesis that there are differences in TL-associated SNPs by race and SEP. We constructed a TL polygenic risk score (PRS) and examined its association with race/ethnicity, educational attainment, assets, gender, and age.U.S. blacks were more likely to have a lower PRS for TL, as were older individuals and men. Racial differences in TL were statistically accounted for when controlling for population structure using genetic principal components. The GWAS-derived SNPs for TL, however, may not have consistent associations with TL across different racial/ethnic groups.This study showed that associations of race/ethnicity with TL differed when accounting for population stratification. The role of race/ethnicity for TL remains uncertain, however, as the genetic determinants of TL may differ by race/ethnicity. Future GWAS samples should include racially diverse participants to allow for better characterization of the determinants of TL in human populations.

    View details for DOI 10.1016/j.ebiom.2016.08.015

    View details for PubMedID 27566956

    View details for PubMedCentralID PMC5049995

  • Reply to Yang et al.: GCTA produces unreliable heritability estimates. Proceedings of the National Academy of Sciences of the United States of America Krishna Kumar, S., Feldman, M. W., Rehkopf, D. H., Tuljapurkar, S. 2016; 113 (32): E4581-?

    View details for DOI 10.1073/pnas.1608425113

    View details for PubMedID 27457962

    View details for PubMedCentralID PMC4987787

  • Equity and length of lifespan are not the same. Proceedings of the National Academy of Sciences of the United States of America Seligman, B., Greenberg, G., Tuljapurkar, S. 2016; 113 (30): 8420-3


    Efforts to understand the dramatic declines in mortality over the past century have focused on life expectancy. However, understanding changes in disparity in age of death is important to understanding mechanisms of mortality improvement and devising policy to promote health equity. We derive a novel decomposition of variance in age of death, a measure of inequality, and apply it to cause-specific contributions to the change in variance among the G7 countries (Canada, France, Germany, Italy, Japan, the United Kingdom, and the United States) from 1950 to 2010. We find that the causes of death that contributed most to declines in the variance are different from those that contributed most to increase in life expectancy; in particular, they affect mortality at younger ages. We also find that, for two leading causes of death [cancers and cardiovascular disease (CVD)], there are no consistent relationships between changes in life expectancy and variance either within countries over time or between countries. These results show that promoting health at younger ages is critical for health equity and that policies to control cancer and CVD may have differing implications for equity.

    View details for DOI 10.1073/pnas.1601112113

    View details for PubMedID 27402750

    View details for PubMedCentralID PMC4968733

  • Distinct genomic architecture of Plasmodium falciparum populations from South Asia. Molecular and biochemical parasitology Kumar, S., Mudeppa, D. G., Sharma, A., Mascarenhas, A., Dash, R., Pereira, L., Shaik, R. B., Maki, J. N., White, J., Zuo, W., Tuljapurkar, S., Duraisingh, M. T., Gomes, E., Chery, L., Rathod, P. K. 2016


    Previous whole genome comparisons of Plasmodium falciparum populations have not included collections from the Indian subcontinent, even though two million Indians contract malaria and about 50,000 die from the disease every year. Stratification of global parasites has revealed spatial relatedness of parasite genotypes on different continents. Here, genomic analysis was further improved to obtain country-level resolution by removing var genes and intergenic regions from distance calculations. P. falciparum genomes from India were found to be most closely related to each other. Their nearest neighbors were from Bangladesh and Myanmar, followed by Thailand. Samples from the rest of Southeast Asia, Africa and South America were increasingly more distant, demonstrating a high-resolution genomic-geographic continuum. Such genome stratification approaches will help monitor variations of malaria parasites within South Asia and future changes in parasite populations that may arise from in-country and cross-border migrations.

    View details for DOI 10.1016/j.molbiopara.2016.07.005

    View details for PubMedID 27457272

  • Linking demographic responses and life history tactics from longitudinal data in mammals OIKOS Gamelon, M., Gaillard, J., Gimenez, O., Coulson, T., Tuljapurkar, S., Baubet, E. 2016; 125 (3): 395-404

    View details for DOI 10.1111/oik.02582

    View details for Web of Science ID 000371222300013

  • The effects of asymmetric competition on the life history of Trinidadian guppies ECOLOGY LETTERS Bassar, R. D., Childs, D. Z., Rees, M., Tuljapurkar, S., Reznick, D. N., Coulson, T. 2016; 19 (3): 268-278


    The effects of asymmetric interactions on population dynamics has been widely investigated, but there has been little work aimed at understanding how life history parameters like generation time, life expectancy and the variance in lifetime reproductive success are impacted by different types of competition. We develop a new framework for incorporating trait-mediated density-dependence into size-structured models and use Trinidadian guppies to show how different types of competitive interactions impact life history parameters. Our results show the degree of symmetry in competitive interactions can have dramatic effects on the speed of the life history. For some vital rates, shifting the competitive superiority from small to large individuals resulted in a doubling of the generation time. Such large influences of competitive symmetry on the timescale of demographic processes, and hence evolution, highlights the interwoven nature of ecological and evolutionary processes and the importance of density-dependence in understanding eco-evolutionary dynamics.

    View details for DOI 10.1111/ele.12563

    View details for Web of Science ID 000369986000006

    View details for PubMedID 26843397

  • Des différences, pourquoi? Transmission, maintenance and effects of phenotypic variance. journal of animal ecology Plard, F., Gaillard, J., Coulson, T., Tuljapurkar, S. 2016; 85 (2): 356-370


    Despite the observed distribution of variable individual phenotypes, survival and reproductive performance in wild populations, models of population dynamics often focus on mean demographic rates. Populations are constituted by individuals with different phenotypes and thus different performances. However, many models of population dynamics provide no understanding of the influence of this phenotypic variation on population dynamics. In this paper, we investigate how the relationships between demographic rates and phenotype distribution influence the transmission and the upholding of phenotypic variation, and population dynamics. We used integral projection models to measure associations between differences of phenotypic trait (size or mass) among individuals and demographic rates, growth and inheritance, and then quantify the influence of phenotypic variation on population dynamics. We build an analytical and general model resulting from simplifications assuming small phenotypic variance. We illustrate our model with two case studies: a short- and a long-lived life history. Population growth rate r is determined by a Lotka style equation in which survival and fertility are averaged over a phenotypic distribution that changes with age. Here, we further decomposed r to show how much it is affected by shifts in phenotypic average as well as variance. We derived the elasticities of r to the first and second derivative of each demographic rate. In particular, we show that the nonlinearity of change in selective pressure with phenotype matters more to population dynamics than the strength of this selection. In other words, the variance of a given trait will be most important when the strength of selection increases (or decreases) nonlinearly with that trait. Inheritance shapes the distribution of newborn phenotypes. Even if newborns have a fixed average phenotype, the variance among newborns increases with phenotypic variance among mothers, strength of inheritance and developmental variation. We explain how the components of inheritance can influence phenotypic variance and thus the demographic rates and population dynamics. In particular, when mothers of different ages produce offspring of different mean phenotype, the inheritance function can have a large influence on both the mean and variance of the trait at different ages and thus on the population growth rate. We provide new tools to understand how phenotypic variation influences population dynamics and discuss in which life histories we expect this influence to be large. For instance, in our short-lived life history, individual variability has larger effect than in our long-lived life history. We conclude by indicating future directions of analysis.

    View details for DOI 10.1111/1365-2656.12477

    View details for PubMedID 26899422

  • Limitations of GCTA as a solution to the missing heritability problem. Proceedings of the National Academy of Sciences of the United States of America Krishna Kumar, S., Feldman, M. W., Rehkopf, D. H., Tuljapurkar, S. 2016; 113 (1): E61-70


    Genome-wide association studies (GWASs) seek to understand the relationship between complex phenotype(s) (e.g., height) and up to millions of single-nucleotide polymorphisms (SNPs). Early analyses of GWASs are commonly believed to have "missed" much of the additive genetic variance estimated from correlations between relatives. A more recent method, genome-wide complex trait analysis (GCTA), obtains much higher estimates of heritability using a model of random SNP effects correlated between genotypically similar individuals. GCTA has now been applied to many phenotypes from schizophrenia to scholastic achievement. However, recent studies question GCTA's estimates of heritability. Here, we show that GCTA applied to current SNP data cannot produce reliable or stable estimates of heritability. We show first that GCTA depends sensitively on all singular values of a high-dimensional genetic relatedness matrix (GRM). When the assumptions in GCTA are satisfied exactly, we show that the heritability estimates produced by GCTA will be biased and the standard errors will likely be inaccurate. When the population is stratified, we find that GRMs typically have highly skewed singular values, and we prove that the many small singular values cannot be estimated reliably. Hence, GWAS data are necessarily overfit by GCTA which, as a result, produces high estimates of heritability. We also show that GCTA's heritability estimates are sensitive to the chosen sample and to measurement errors in the phenotype. We illustrate our results using the Framingham dataset. Our analysis suggests that results obtained using GCTA, and the results' qualitative interpretations, should be interpreted with great caution.

    View details for DOI 10.1073/pnas.1520109113

    View details for PubMedID 26699465

    View details for PubMedCentralID PMC4711841

  • Sex-specific demography and generalization of the Trivers-Willard theory. Nature Schindler, S., Gaillard, J., Grüning, A., Neuhaus, P., Traill, L. W., Tuljapurkar, S., Coulson, T. 2015; 526 (7572): 249-252

    View details for DOI 10.1038/nature14968

    View details for PubMedID 26390152

  • Quantifying the influence of measured and unmeasured individual differences on demography JOURNAL OF ANIMAL ECOLOGY Plard, F., Gaillard, J., Coulson, T., Delorme, D., Warnant, C., Michallet, J., Tuljapurkar, S., Krishnakumar, S., Bonenfant, C. 2015; 84 (5): 1434-1445
  • Quantifying the influence of measured and unmeasured individual differences on demography. The Journal of animal ecology Plard, F., Gaillard, J. M., Coulson, T., Delorme, D., Warnant, C., Michallet, J., Tuljapurkar, S., Krishnakumar, S., Bonenfant, C. 2015; 84 (5): 1434-45


    1. Demographic rates can vary not only with measured individual characters like age, sex and mass but also with unmeasured individual variables like behaviour, genes and health. 2. Predictions from population models that include measured individual characteristics often differ from models that exclude them. Similarly, unmeasured individual differences have the potential to impact predictions from population models. However, unmeasured individual differences are rarely included in population models. 3. We construct stage- and age-structured models (where stage is mass) of a roe deer population, which are parameterized from statistical functions that either include, or ignore, unmeasured individual differences. 4. We found that mass and age structures substantially impacted model parameters describing population dynamics, as did temporal environmental variation, while unmeasured individual differences impacted parameters describing population dynamics to a much smaller extent once individual heterogeneity related to mass and age has been included in the model. We discuss how our assumptions (unmeasured individual differences only in mean trait values) could have influenced our findings and under what circumstances unmeasured individual differences could have had a larger impact on population dynamics. 5. There are two reasons explaining the relative small influence of unmeasured individual differences on population dynamics in roe deer. First, individual body mass and age both capture a large amount of individual differences in roe deer. Second, in large populations of long-lived animals, the average quality of individuals (independent of age and mass) within the population is unlikely to show substantial variation over time, unless rapid evolution is occurring. So even though a population consisting of high-quality individuals would have much higher population growth rate than a population consisting of low-quality individuals, the probability of observing a population consisting only of high-quality individuals is small.

    View details for DOI 10.1111/1365-2656.12393

    View details for PubMedID 26140296

    View details for PubMedCentralID PMC5642278

  • Measuring selective constraint on fertility in human life histories PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Jones, J. H., Tuljapurkar, S. 2015; 112 (29): 8982-8986


    Human life histories combine late age at first reproduction, long reproductive span, relatively high fertility, and substantial postreproductive survival. However, even among the most fecund populations, human fertility falls far below its theoretical maximum. The extent of parental care required for successful offspring recruitment and widespread fertility decline under proper economic conditions suggest that selection on fertility is constrained by trade-offs with recruitment. Here we measure the trade-offs between life history traits under selection by approximating the slope of the selective constraint curve on two traits at the observed values. Using a selection of populations that span human demographic space, we find that the substitution elasticity of fertility for infant survival shows age-related patterns, with minimum substitution elasticities ranging from 14 to 22 for the four populations. The age of this minimum occurs earlier in the high-mortality populations relative to generation time than it does in the low-mortality populations. The human curves are qualitatively similar to one of two comparable nonhuman primate age-specific substitution elasticity curves. The curve for rhesus macaques has a similar shape but is shifted down, meaning that the threshold for switching from investing in survival to fertility is lower at all ages. The magnitude of the substitution elasticities is similar between chimpanzees and humans but the shape is quite different, rising more slowly for a longer fraction of the chimpanzee life cycle. The steeply rising substitution elasticities with age in humans has clear implications for the evolution of reproductive senescence.

    View details for DOI 10.1073/pnas.1422037112

    View details for Web of Science ID 000358225100062

    View details for PubMedID 26150499

    View details for PubMedCentralID PMC4517261

  • Influence of Life-History Tactics on Transient Dynamics: A Comparative Analysis across Mammalian Populations AMERICAN NATURALIST Gamelon, M., Gimenez, O., Baubet, E., Coulson, T., Tuljapurkar, S., Gaillard, J. 2014; 184 (5): 673-683

    View details for DOI 10.1086/677929

    View details for Web of Science ID 000344110400014

  • Influence of life-history tactics on transient dynamics: a comparative analysis across mammalian populations. American naturalist Gamelon, M., Gimenez, O., Baubet, E., Coulson, T., Tuljapurkar, S., Gaillard, J. 2014; 184 (5): 673-683


    Most mammalian populations suffer from natural or human-induced disturbances; populations are no longer at the equilibrium (i.e., at stable [st]age distribution) and exhibit transient dynamics. From a literature survey, we studied patterns of transient dynamics for mammalian species spanning a large range of life-history tactics and population growth rates. For each population, we built an age-structured matrix and calculated six metrics of transient dynamics. After controlling for possible confounding effects of the phylogenetic relatedness among species using a phylogenetic principal component analysis and phylogenetic generalized least squares models, we found that short-term demographic responses of mammalian populations to disturbance are shaped by generation time and growth rate. Species with a slow pace of life (i.e., species with a late maturity, a low fecundity, and a long life span) displayed decreases in population size after a disturbance, whereas fast-living species increased in population size. The magnitude of short-term variation in population size increased with asymptotic population growth, being buffered in slow-growing species (i.e., species with a low population growth rate) but large in fast-growing species. By demonstrating direct links between transient dynamics, life history (generation time), and ecology (demographic regime), our comparative analysis of transient dynamics clearly improves our understanding of population dynamics in variable environments and has clear implications for future studies of the interplay between evolutionary and ecological dynamics. As most populations in the wild are not at equilibrium, we recommend that analyses of transient dynamics be performed when studying population dynamics in variable environments.

    View details for DOI 10.1086/677929

    View details for PubMedID 25325750

  • Birth-order differences can drive natural selection on aging. Evolution; international journal of organic evolution Gillespie, D. O., Trotter, M. V., Krishna-Kumar, S., Tuljapurkar, S. D. 2014; 68 (3): 886-892


    Senescence-the deterioration of survival and reproductive capacity with increasing age-is generally held to be an evolutionary consequence of the declining strength of natural selection with increasing age. The diversity in rates of aging observed in nature suggests that the rate at which age-specific selection weakens is determined by species-specific ecological factors. We propose that, in iteroparous species, relationships between parental age, offspring birth order, and environment may affect selection on senescence. Later-born siblings have, on average, older parents than do first borns. Offspring born to older parents may experience different environments in terms of family support or inherited resources, factors often mediated by competition from siblings. Thus, age-specific selection on parents may change if the environment produces birth-order related gradients in reproductive success. We use an age-and-stage structured population model to investigate the impact of sibling environmental inequality on the expected evolution of senescence. We show that accelerated senescence evolves when later-born siblings are likely to experience an environment detrimental to lifetime reproduction. In general, sibling inequality is likely to be of particular importance for the evolution of senescence in species such as humans, where family interactions and resource inheritance have important roles in determining lifetime reproduction.

    View details for DOI 10.1111/evo.12319

    View details for PubMedID 24274174

  • The invisible cliff: abrupt imposition of malthusian equilibrium in a natural-fertility, agrarian society. PloS one Puleston, C., Tuljapurkar, S., Winterhalder, B. 2014; 9 (1)


    Analysis of a natural fertility agrarian society with a multi-variate model of population ecology isolates three distinct phases of population growth following settlement of a new habitat: (1) a sometimes lengthy copial phase of surplus food production and constant vital rates; (2) a brief transition phase in which food shortages rapidly cause increased mortality and lessened fertility; and (3) a Malthusian phase of indefinite length in which vital rates and quality of life are depressed, sometimes strikingly so. Copial phase duration declines with increases in the size of the founding group, maximum life expectancy and fertility; it increases with habitat area and yield per hectare; and, it is unaffected by the sensitivity of vital rates to hunger. Transition phase duration is unaffected by size of founding population and area of settlement; it declines with yield, life expectancy, fertility and the sensitivity of vital rates to hunger. We characterize the transition phase as the Malthusian transition interval (MTI), in order to highlight how little time populations generally have to adjust. Under food-limited density dependence, the copial phase passes quickly to an equilibrium of grim Malthusian constraints, in the manner of a runner dashing over an invisible cliff. The three-phase pattern diverges from widely held intuitions based on standard Lotka-Verhulst approaches to population regulation, with implications for the analysis of socio-cultural evolution, agricultural intensification, bioarchaeological interpretation of food stress in prehistoric societies, and state-level collapse.

    View details for DOI 10.1371/journal.pone.0087541

    View details for PubMedID 24498131

    View details for PubMedCentralID PMC3909123

  • Defoliation and bark harvesting affect life-history traits of a tropical tree JOURNAL OF ECOLOGY Gaoue, O. G., Horvitz, C. C., Ticktin, T., Steiner, U. K., Tuljapurkar, S. 2013; 101 (6): 1563-1571
  • Contributions of Covariance: Decomposing the Components of Stochastic Population Growth in Cypripedium calceolus AMERICAN NATURALIST Davison, R., Nicole, F., Jacquemyn, H., Tuljapurkar, S. 2013; 181 (3): 410-420


    Although correlations between vital rates can have important effects on evolution and demography, few studies have investigated their effects on population dynamics. Here, we extend life-table response experiments (LTREs) to variable environments, showing how to quantify contributions made by (1) mean vital rates, (2) variability driven by environmental fluctuations, (3) correlations implying demographic trade-offs and reflecting stage transition synchrony, and (4) elasticities reflecting local selection pressures. Applying our methods to the lady's slipper orchid Cypripedium calceolus, we found that mean rates accounted for 77.1% of all effects on the stochastic growth rate, variability accounted for 12.6%, elasticities accounted for 6.6%, and correlations accounted for 3.7%. Stochastic effects accounted for 17.6%, 15.3%, and 35.9% of the total in our three populations. Larger elasticities to transitions between dormancy states and stronger correlations between emergence and survival suggest that one population was under greater pressure to remain active while the other two showed survival payoffs for dormancy in poor years. Strong negative correlations between dormancy, emergence, and stasis balanced opposing contributions, resulting in near stationarity in two populations. These new methods provide an additional tool for researchers investigating stochastic population dynamics and should be useful for a broad range of applications in basic ecology and conservation biology.

    View details for DOI 10.1086/669155

    View details for PubMedID 23448889

  • Beyond the Mean: Sensitivities of the Variance of Population Growth. Methods in ecology and evolution Trotter, M. V., Krishna-Kumar, S., Tuljapurkar, S. 2013; 4 (3): 290-298


    Populations in variable environments are described by both a mean growth rate and a variance of stochastic population growth. Increasing variance will increase the width of confidence bounds around estimates of population size, growth, probability of and time to quasi-extinction. However, traditional sensitivity analyses of stochastic matrix models only consider the sensitivity of the mean growth rate. We derive an exact method for calculating the sensitivity of the variance in population growth to changes in demographic parameters. Sensitivities of the variance also allow a new sensitivity calculation for the cumulative probability of quasi-extinction. We apply this new analysis tool to an empirical dataset on at-risk polar bears to demonstrate its utility in conservation biology We find that in many cases a change in life history parameters will increase both the mean and variance of population growth of polar bears. This counterintuitive behaviour of the variance complicates predictions about overall population impacts of management interventions. Sensitivity calculations for cumulative extinction risk factor in changes to both mean and variance, providing a highly useful quantitative tool for conservation management. The mean stochastic growth rate and its sensitivities do not fully describe the dynamics of population growth. The use of variance sensitivities gives a more complete understanding of population dynamics and facilitates the calculation of new sensitivities for extinction processes.

    View details for DOI 10.1111/2041-210X.12010

    View details for PubMedID 26635948

    View details for PubMedCentralID PMC4666685

  • Beyond the mean: sensitivities of the variance of population growth METHODS IN ECOLOGY AND EVOLUTION Trotter, M. V., Krishna-Kumar, S., Tuljapurkar, S. 2013; 4 (3): 290-298
  • Structured Population Models: Introduction THEORETICAL POPULATION BIOLOGY Tuljapurkar, S., Coulson, T., Steiner, U. K. 2012; 82 (4): 241-243

    View details for DOI 10.1016/j.tpb.2012.10.007

    View details for Web of Science ID 000311981400001

    View details for PubMedID 23174426

  • Linking the population growth rate and the age-at-death distribution THEORETICAL POPULATION BIOLOGY Schindler, S., Tuljapurkar, S., Gaillard, J., Coulson, T. 2012; 82 (4): 244-252


    The population growth rate is linked to the distribution of age at death. We demonstrate that this link arises because both the birth and death rates depend on the variance of age-at-death. This bears the prospect to separate the influences of the age patterns of fertility and mortality on population growth rate. Here, we show how the age pattern of death affects population growth. Using this insight we derive a new approximation of the population growth rate that uses the first and second moments of the age-at-death distribution. We apply our new approximation to 46 mammalian life tables (including humans) and show that it is on par with the most prominent other approximations.

    View details for DOI 10.1016/j.tpb.2012.09.003

    View details for Web of Science ID 000311981400002

    View details for PubMedID 23103877

  • Editorial for the Special Issue: Biodemographic determinants of lifespan EXPERIMENTAL GERONTOLOGY Carey, J. R., Tuljapurkar, S., Wachter, K. 2012; 47 (10): 755-758

    View details for DOI 10.1016/j.exger.2012.08.003

    View details for Web of Science ID 000308667600001

    View details for PubMedID 22917860

  • Building and testing models of long-term agricultural intensification and population dynamics: A case study from the Leeward Kohala Field System, Hawai'i ECOLOGICAL MODELLING Kirch, P. V., Asner, G., Chadwick, O. A., Field, J., LADEFOGED, T., Lee, C., Puleston, C., Tuljapurkar, S., Vitousek, P. M. 2012; 227: 18-28
  • Stochastic LTRE analysis of the effects of herbivory on the population dynamics of a perennial grassland herb OIKOS Jacquemyn, H., Brys, R., Davison, R., Tuljapurkar, S., Jongejans, E. 2012; 121 (2): 211-218
  • Derivatives of the stochastic growth rate THEORETICAL POPULATION BIOLOGY Steinsaltz, D., Tuljapurkar, S., Horvitz, C. 2011; 80 (1): 1-15


    We consider stochastic matrix models for population driven by random environments which form a Markov chain. The top Lyapunov exponent a, which describes the long-term growth rate, depends smoothly on the demographic parameters (represented as matrix entries) and on the parameters that define the stochastic matrix of the driving Markov chain. The derivatives of a-the "stochastic elasticities"-with respect to changes in the demographic parameters were derived by Tuljapurkar (1990). These results are here extended to a formula for the derivatives with respect to changes in the Markov chain driving the environments. We supplement these formulas with rigorous bounds on computational estimation errors, and with rigorous derivations of both the new and old formulas.

    View details for DOI 10.1016/j.tpb.2011.03.004

    View details for Web of Science ID 000292353700001

    View details for PubMedID 21463645

  • Variance in death and its implications for modeling and forecasting mortality DEMOGRAPHIC RESEARCH Tuljapurkar, S., Edwards, R. D. 2011; 24: 497-525
  • Variance in Death and Its Implications for Modeling and Forecasting Mortality. Demographic research Tuljapurkar, S., Edwards, R. D. 2011; 24: 497-526


    The slope and curvature of the survivorship function reflect the considerable amount of variance in length of life found in any human population. Part is due to the well-known variation in life expectancy between groups: large differences according to race, sex, socioeconomic status, or other covariates. But within-group variance is large even in narrowly defined groups, and changes substantially and inversely with the group average length of life. We show that variance in length of life is inversely related to the Gompertz slope of log mortality through age, and we reveal its relationship to variance in a multiplicative frailty index. Our findings bear a variety of implications for modeling and forecasting mortality. In particular, we examine how the assumption of proportional hazards fails to account adequately for differences in subgroup variance, and we discuss how several common forecasting models treat the variance along the temporal dimension.

    View details for DOI 10.4054/DemRes.2011.24.21

    View details for PubMedID 25328439

    View details for PubMedCentralID PMC4197997

  • Demography as the Human Story POPULATION AND DEVELOPMENT REVIEW Tuljapurkar, S. 2011; 37 (1): 166-171

    View details for Web of Science ID 000287966500007

    View details for PubMedID 21735616

  • Static and dynamic expression of life history traits in the Northern Fulmar (Fulmarus glacialis). Oikos (Copenhagen, Denmark) Orzack, S. H., Steiner, U. K., Tuljapurkar, S., Thompson, P. 2011; 120 (3): 369-380


    Understanding the static and dynamic expression of life history traits is a prerequisite for the development of a causal theory of the evolution of aging and of life histories. We analyzed the statics and dynamics of reproduction and survival in a wild population of the Northern Fulmar, Fulmarus glacialis (Procellaridae). Survival rate is most influenced by year as compared to age and cohort. When temporal variation is ignored, survival rate increases slowly with age and then declines more rapidly at late ages. Survival rate contingent upon reproductive "stratum" (producing an egg, hatching an egg, fledging a hatchling) also exhibits this pattern. Survival and reproduction have a positive static association in that survival rate increases as the apparent energy allocated to reproduction increases (as indexed by stratum). There is a broad distribution of realized lifetime reproductive success, which could be due to "fixed" heterogeneity, with some individuals always having low survival and reproduction and others always having high survival and reproduction, or be due to "dynamic" heterogeneity, with all individuals having the same expected reproductive and survival rates. Analysis of stochastic stratum dynamics indicates that individuals do not remain long in any given stratum and suggest that the variation among individuals with respect to lifetime reproductive success is due to dynamic heterogeneity. The probability of producing an egg increases with age for both sexes, whereas the probability of producing a fledgling initially declines with age and then increases. These results underscore the necessity of understanding the static and dynamic expression of demographic traits when making a causal claim about their evolution.

    View details for DOI 10.1111/j.1600-0706.2010.17996.x

    View details for PubMedID 29093607

    View details for PubMedCentralID PMC5661999

  • Static and dynamic expression of life history traits in the northern fulmar Fulmarus glacialis OIKOS Orzack, S. H., Steiner, U. K., Tuljapurkar, S., Thompson, P. 2011; 120 (3): 369-380

    View details for DOI 10.1086/657141

    View details for Web of Science ID 000284000800003

  • A new way to integrate selection when both demography and selection gradients vary over time. International journal of plant sciences Horvitz, C. C., Coulson, T., Tuljapurkar, S., Schemske, D. W. 2010; 171 (9): 945-959


    When both selection and demography vary over time, how can the long-run expected strength of selection on quantitative traits be measured? There are two basic steps in the proposed new analysis: one relates trait values to fitness components and the other relates fitness components to total fitness. We used one population projection matrix for each state of the environment together with a model of environmental dynamics, defining total fitness as the stochastic growth rate. We multiplied environment-specific, stage-specific mean-standardized selection gradients by environment-specific, stage-specific elasticities of the stochastic growth rate, summing over all relevant life history and environmental paths. Our two example traits were floral tube length in a rainforest herb and the timing of birth in Red Deer. For each species, we constructed two models of environmental dynamics, including one based on historical climate records. We found that total integrated selection, as well as the relative contributions of life-history pathways and environments, varied with environmental dynamics. Temporal patterning in the environment has selective consequences. Linking models of environmental change to relevant short term data on demography and selection may permit estimation of the force of selection over the long-term in variable environments.

    View details for DOI 10.1086/657141

    View details for PubMedID 25089083

    View details for PubMedCentralID PMC4115803

  • Using evolutionary demography to link life history theory, quantitative genetics and population ecology JOURNAL OF ANIMAL ECOLOGY Coulson, T., Tuljapurkar, S., Childs, D. Z. 2010; 79 (6): 1226-1240


    1. There is a growing number of empirical reports of environmental change simultaneously influencing population dynamics, life history and quantitative characters. We do not have a well-developed understanding of links between the dynamics of these quantities. 2. Insight into the joint dynamics of populations, quantitative characters and life history can be gained by deriving a model that allows the calculation of fundamental quantities that underpin population ecology, evolutionary biology and life history. The parameterization and analysis of such a model for a specific system can be used to predict how a population will respond to environmental change. 3. Age-stage-structured models can be constructed from character-demography associations that describe age-specific relationships between the character and: (i) survival; (ii) fertility; (iii) ontogenetic development of the character among survivors; and (iv) the distribution of reproductive allocation. 4. These models can be used to calculate a wide range of useful biological quantities including population growth and structure; terms in the Price equation including selection differentials; estimates of biometric heritabilities; and life history descriptors including generation time. We showcase the method through parameterization of a model using data from a well-studied population of Soay sheep Ovis aries. 5. Perturbation analysis is used to investigate how the quantities listed in summary point 4 change as each parameter in each character-demography function is altered. 6. A wide range of joint dynamics of life history, quantitative characters and population growth can be generated in response to changes in different character-demography associations; we argue this explains the diversity of observations on the consequences of environmental change from studies of free-living populations. 7. The approach we describe has the potential to explain within and between species patterns in quantitative characters, life history and population dynamics.

    View details for DOI 10.1111/j.1365-2656.2010.01734.x

    View details for Web of Science ID 000283074000010

    View details for PubMedID 20704627

  • Coupled dynamics of body mass and population growth in response to environmental change NATURE Ozgul, A., Childs, D. Z., Oli, M. K., Armitage, K. B., Blumstein, D. T., Olson, L. E., Tuljapurkar, S., Coulson, T. 2010; 466 (7305): 482-U5


    Environmental change has altered the phenology, morphological traits and population dynamics of many species. However, the links underlying these joint responses remain largely unknown owing to a paucity of long-term data and the lack of an appropriate analytical framework. Here we investigate the link between phenotypic and demographic responses to environmental change using a new methodology and a long-term (1976-2008) data set from a hibernating mammal (the yellow-bellied marmot) inhabiting a dynamic subalpine habitat. We demonstrate how earlier emergence from hibernation and earlier weaning of young has led to a longer growing season and larger body masses before hibernation. The resulting shift in both the phenotype and the relationship between phenotype and fitness components led to a decline in adult mortality, which in turn triggered an abrupt increase in population size in recent years. Direct and trait-mediated effects of environmental change made comparable contributions to the observed marked increase in population growth. Our results help explain how a shift in phenology can cause simultaneous phenotypic and demographic changes, and highlight the need for a theory integrating ecological and evolutionary dynamics in stochastic environments.

    View details for DOI 10.1038/nature09210

    View details for Web of Science ID 000280141200034

    View details for PubMedID 20651690

  • Plant populations track rather than buffer climate fluctuations ECOLOGY LETTERS Jongejans, E., De Kroon, H., Tuljapurkar, S., Shea, K. 2010; 13 (6): 736-743


    Climate change not only affects mean temperature and precipitation but also exacerbates temporal fluctuations in these conditions. However, we know relatively little about how species respond to such climate fluctuations, with respect to variation in vital rates (i.e. survival, growth and reproduction of individuals) and population fluctuations. We examine whether populations display evidence of buffering against environmental variation in one of two ways: (1) through negative covariances among vital rates, or (2) reduction of variation in those vital rates to which population growth is most sensitive. We analyse time series of demographic data for 40 plant species and show that there is no evidence for either of these mechanisms. In species in which there is evidence for vital rate covariation, positive covariances between reproduction and survival rates predominate, and tend to magnify the effect of variability. Increasing climate variability is therefore expected to increase population fluctuations and extinction risks.

    View details for DOI 10.1111/j.1461-0248.2010.01470.x

    View details for Web of Science ID 000277867100008

    View details for PubMedID 20426793

  • Dynamic heterogeneity and life history variability in the kittiwake JOURNAL OF ANIMAL ECOLOGY Steiner, U. K., Tuljapurkar, S., Orzack, S. H. 2010; 79 (2): 436-444


    1. Understanding the evolution of life histories requires an assessment of the process that generates variation in life histories. Within-population heterogeneity of life histories can be dynamically generated by stochastic variation of reproduction and survival or be generated by individual differences that are fixed at birth. 2. We show for the kittiwake that dynamic heterogeneity is a sufficient explanation of observed variation of life histories. 3. The total heterogeneity in life histories has a small contribution from reproductive stage dynamics and a large contribution from survival differences. We quantify the diversity in life histories by metrics computed from the generating stochastic process. 4. We show how dynamic heterogeneity can be used as a null model and also how it can lead to positive associations between reproduction and survival across the life span. 5. We believe our approach to identifying the nature of among-individual heterogeneity yields important insights into the forces that generate within-population variation of life-history traits. It provides an alternative to claims that fixed individual differences are a major determinant of heterogeneity in life histories.

    View details for DOI 10.1111/j.1365-2656.2009.01653.x

    View details for Web of Science ID 000274321200016

    View details for PubMedID 20102422

  • Demographic effects of extreme weather events on a short-lived calcareous grassland species: stochastic life table response experiments JOURNAL OF ECOLOGY Davison, R., Jacquemyn, H., Adriaens, D., Honnay, O., De Kroon, H., Tuljapurkar, S. 2010; 98 (2): 255-267
  • Environmental variance, population growth and evolution JOURNAL OF ANIMAL ECOLOGY Tuljapurkar, S. 2010; 79 (1): 1-3


    Environmental fluctuations on time scales of one to tens of generations are increasingly recognized as important determinants of population dynamics and microevolution. Jonzén et al. in this issue analyse how the vital rates of red kangaroos depend on annual rainfall, and estimate the elasticities of stochastic growth rate to the means and variances of the vital rates, as well as to the mean and variance of rainfall. Their results demonstrate how ecological and evolutionary studies can benefit from including explicit environmental drivers when modelling populations, and from the use of mean and variance elasticities.

    View details for DOI 10.1111/j.1365-2656.2009.01619.x

    View details for Web of Science ID 000272656600001

    View details for PubMedID 20409157

  • Population and prehistory III: Food-dependent demography in variable environments THEORETICAL POPULATION BIOLOGY Lee, C. T., Puleston, C. O., Tuljapurkar, S. 2009; 76 (3): 179-188


    The population dynamics of preindustrial societies depend intimately on their surroundings, and food is a primary means through which environment influences population size and individual well-being. Food production requires labor; thus, dependence of survival and fertility on food involves dependence of a population's future on its current state. We use a perturbation approach to analyze the effects of random environmental variation on this nonlinear, age-structured system. We show that in expanding populations, direct environmental effects dominate induced population fluctuations, so environmental variability has little effect on mean hunger levels, although it does decrease population growth. The growth rate determines the time until population is limited by space. This limitation introduces a tradeoff between population density and well-being, so population effects become more important than the direct effects of the environment: environmental fluctuation increases mortality, releasing density dependence and raising average well-being for survivors. We discuss the social implications of these findings for the long-term fate of populations as they transition from expansion into limitation, given that conditions leading to high well-being during growth depress well-being during limitation.

    View details for DOI 10.1016/j.tpd.2009.06.003

    View details for Web of Science ID 000271283500003

    View details for PubMedID 19540865

  • A time to grow and a time to die: a new way to analyze the dynamics of size, light, age, and death of tropical trees ECOLOGY Metcalf, C. J., Horvitz, C. C., Tuljapurkar, S., Clark, D. A. 2009; 90 (10): 2766-2778


    In tropical rain forests, rates of forest turnover and tree species' life-history differences are shaped by the life expectancy of trees and the time taken by seedlings to reach the canopy. These measures are therefore of both theoretical and applied interest. However, the relationship between size, age, and life expectancy is poorly understood. In this paper, we show how to obtain, in a dynamic environment, age-related population parameters from data on size and light transitions and survival of individuals over single time steps. We accomplish this goal by combining two types of analysis (integral projection modeling and age-from-stage analysis for variable environments) in a new way. The method uses an index of crown illumination (CI) to capture the key tree life-history axis of movement through the light environment. We use this method to analyze data on nine tropical tree species, chosen to sample two main gradients, juvenile recruitment niche (gap/nongap) and adult crown position niche (subcanopy, canopy-emergent). We validate the method using independent estimates of age and size from growth rings and 14C from some of the same species at the same site and use our results to examine correlations among age-related population parameters. Finally, we discuss the implications of these new results for life histories of tropical trees.

    View details for Web of Science ID 000270274200013

    View details for PubMedID 19886486

  • DEMOGRAPHY Babies make a comeback NATURE Tuljapurkar, S. 2009; 460 (7256): 693-694

    View details for DOI 10.1038/460693a

    View details for Web of Science ID 000268670300025

    View details for PubMedID 19661903

  • Estimating stochastic elasticities directly from longitudinal data ECOLOGY LETTERS Haridas, C. V., Tuljapurkar, S., Coulson, T. 2009; 12 (8): 806-812


    The elasticities of long-run population growth rate with respect to vital rates are useful in studying selection on vital rates, and in evaluating management policy that aims to control vital rates. In temporally varying environments, elasticity is often calculated from simulations that assume a probability distribution for the environmental states. Here we develop a method to estimate elasticities directly from demographic data. Using a time-series of demographic matrices and age-structure we construct a consistent statistical estimator of elasticity that converges to the correct limiting value as the sample length increases. We also construct confidence intervals for elasticities from temporal data and suggest tools for testing hypotheses about the strength of selection. We use data on a natural population to show that our method can indeed accurately estimate elasticities using relatively short time series.

    View details for DOI 10.1111/j.1461-0248.2009.01330.x

    View details for Web of Science ID 000267660600009

    View details for PubMedID 19552649

  • The Dynamics of Phenotypic Change and the Shrinking Sheep of St. Kilda SCIENCE Ozgul, A., Tuljapurkar, S., Benton, T. G., Pemberton, J. M., Clutton-Brock, T. H., Coulson, T. 2009; 325 (5939): 464-467


    Environmental change, including climate change, can cause rapid phenotypic change via both ecological and evolutionary processes. Because ecological and evolutionary dynamics are intimately linked, a major challenge is to identify their relative roles. We exactly decomposed the change in mean body weight in a free-living population of Soay sheep into all the processes that contribute to change. Ecological processes contribute most, with selection--the underpinning of adaptive evolution--explaining little of the observed phenotypic trend. Our results enable us to explain why selection has so little effect even though weight is heritable, and why environmental change has caused a decline in the body size of Soay sheep.

    View details for DOI 10.1126/science.1173668

    View details for Web of Science ID 000268255100053

    View details for PubMedID 19574350

  • From stochastic environments to life histories and back PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES Tuljapurkar, S., Gaillard, J., Coulson, T. 2009; 364 (1523): 1499-1509


    Environmental stochasticity is known to play an important role in life-history evolution, but most general theory assumes a constant environment. In this paper, we examine life-history evolution in a variable environment, by decomposing average individual fitness (measured by the long-run stochastic growth rate) into contributions from average vital rates and their temporal variation. We examine how generation time, demographic dispersion (measured by the dispersion of reproductive events across the lifespan), demographic resilience (measured by damping time), within-year variances in vital rates, within-year correlations between vital rates and between-year correlations in vital rates combine to determine average individual fitness of stylized life histories. In a fluctuating environment, we show that there is often a range of cohort generation times at which the fitness is at a maximum. Thus, we expect 'optimal' phenotypes in fluctuating environments to differ from optimal phenotypes in constant environments. We show that stochastic growth rates are strongly affected by demographic dispersion, even when deterministic growth rates are not, and that demographic dispersion also determines the response of life-history-specific average fitness to within- and between-year correlations. Serial correlations can have a strong effect on fitness, and, depending on the structure of the life history, may act to increase or decrease fitness. The approach we outline takes a useful first step in developing general life-history theory for non-constant environments.

    View details for DOI 10.1098/rstb.2009.0021

    View details for Web of Science ID 000265732200003

    View details for PubMedID 19414465

    View details for PubMedCentralID PMC2690509

  • Hierarchical demography: a general approach with an application to honey bees ECOLOGY Al-Khafaji, K., Tuljapurkar, S., Carey, J. R., Page, R. E. 2009; 90 (2): 556-566


    Hierarchical population structure, where individuals are aggregated into colonies or similar groups that themselves grow, survive or perish, and potentially produce offspring groups, is an important feature of many biological systems, most notably eusocial organisms such as the honey bee, Apis mellifera. Despite this hierarchical structure, there is a paucity of analytical models and theory linking the dynamics of individuals within colonies to the dynamics of a population of colonies. We present an analytical framework that provides a simple, robust, and predictive theory for the population dynamics of hierarchical organisms. Our framework explicitly describes and links demographic dynamics for the different levels in the hierarchy (individuals, groups, population). We illustrate the application of the framework by developing a model for honey bees and analyzing the effects of life history traits such as worker life span and size at swarming on the growth rate of populations. We conclude by discussing possible extensions of the model that increase its realism and expand its usefulness beyond swarm-founding, monogynous, eusocial insects.

    View details for Web of Science ID 000263570800030

    View details for PubMedID 19323239

  • Dynamic heterogeneity in life histories ECOLOGY LETTERS Tuljapurkar, S., Steiner, U. K., Orzack, S. H. 2009; 12 (1): 93-106


    Longitudinal data on natural populations have been analysed using multistage models in which survival depends on reproductive stage, and individuals change stages according to a Markov chain. These models are special cases of stage-structured population models. We show that stage-structured models generate dynamic heterogeneity: life-history differences produced by stochastic stratum dynamics. We characterize dynamic heterogeneity in a range of species across taxa by properties of the Markov chain: the entropy, which describes the extent of heterogeneity, and the subdominant eigenvalue, which describes the persistence of reproductive success during the life of an individual. Trajectories of reproductive stage determine survivorship, and we analyse the variance in lifespan within and between trajectories of reproductive stage. We show how stage-structured models can be used to predict realized distributions of lifetime reproductive success. Dynamic heterogeneity contrasts with fixed heterogeneity: unobserved differences that generate variation between life histories. We show by an example that observed distributions of lifetime reproductive success are often consistent with the claim that little or no fixed heterogeneity influences this trait. We propose that dynamic heterogeneity provides a 'neutral' model for assessing the possible role of unobserved 'quality' differences between individuals. We discuss fitness for dynamic life histories, and the implications of dynamic heterogeneity for the evolution of life histories and senescence.

    View details for DOI 10.1111/j.1461-0248.2008.01262.x

    View details for Web of Science ID 000261625500011

    View details for PubMedID 19016825

  • Evolution of Delayed Reproduction in Uncertain Environments: A Life-History Perspective AMERICAN NATURALIST Koons, D. N., Metcalf, C. J., Tuljapurkar, S. 2008; 172 (6): 797-805


    Environmental uncertainty alone can select for delayed reproduction; however, its relative role in the evolution of delayed reproduction across life histories is not known. Along a life-history spectrum from low-survival/high-fertility species to high-survival/low-fertility species, we show that the latter are more likely to evolve delayed reproduction if fertility varies over time. By contrast, if survival varies over time, low-survival life histories are more likely to evolve delays. If there is variation in both survival and fertility, and if this variation is positively associated, the evolutionarily stable reproductive delay is decreased (relative to independent variation in survival and fertility). Conversely, if variation in survival and fertility is negatively associated, the evolutionarily stable reproductive delay is increased. We further show that environmental uncertainty can drive the evolution of delayed reproduction in an iteroparous organism but only in the special case where juvenile survival is greater than adult survival. For common iteroparous life histories (adult survival > juvenile survival), environmental uncertainty does not select for delayed reproduction. Thus, any benefits that delayed reproduction might have on reproduction or survival could be especially important in explaining the common observation of delayed reproduction in many vertebrates and perennial plants.

    View details for DOI 10.1086/592867

    View details for Web of Science ID 000261235500009

    View details for PubMedID 18959491

  • The Dynamics of a Quantitative Trait in an Age-Structured Population Living in a Variable Environment AMERICAN NATURALIST Coulson, T., Tuljapurkar, S. 2008; 172 (5): 599-612


    Time series of rapid phenotypic change have been documented in age-structured populations living in the wild. Researchers are often interested in identifying the processes responsible for such change. We derive an equation to exactly decompose change in the mean value of a phenotypic trait into contributions from fluctuations in the demographic structure and age-specific viability selection, fertility selection, phenotypic plasticity, and differences between offspring and parental trait values. We treat fitness as a sum of its components rather than as a scalar and explicitly consider age structure by focusing on short time steps, which are appropriate for describing phenotypic change in species with overlapping generations. We apply the method to examine stasis in birth weight in a well-characterized population of red deer. Stasis is achieved because positive viability selection for an increase in birth weight is countered by parents producing offspring that are, on average, smaller than they were at birth. This is one of many ways in which equilibria in the mean value of a phenotypic trait can be maintained. The age-structured Price equation we derive has the potential to provide considerable insight into the processes generating now frequently reported cases of rapid phenotypic change.

    View details for DOI 10.1086/591693

    View details for Web of Science ID 000260186000001

    View details for PubMedID 18840061

  • How can economic schemes curtail the increasing sex ratio at birth in China? DEMOGRAPHIC RESEARCH Bhattacharjya, D., Sudarshan, A., Tuljapurkar, S., Shachter, R., Feldman, M. 2008; 19: 1831-1850


    Fertility decline, driven by the one-child policy, and son preference have contributed to an alarming difference in the number of live male and female births in China. We present a quantitative model where people choose to sex-select because they perceive that married sons are more valuable than married daughters. Due to the predominant patrilocal kinship system in China, daughters-in-law provide valuable emotional and financial support, enhancing the perceived present value of married sons. We argue that inter-generational transfer data will help ascertain the extent to which economic schemes (such as pension plans for families with no sons) can curtail the increasing sex ratio at birth.

    View details for Web of Science ID 000259977900001

    View details for PubMedCentralID PMC2990196

  • How can economic schemes curtail the increasing sex ratio at birth in China? Demographic research Bhattacharjya, D., Sudarshan, A., Tuljapurkar, S., Shachter, R., Feldman, M. 2008; 19 (54): 1831-1850


    Fertility decline, driven by the one-child policy, and son preference have contributed to an alarming difference in the number of live male and female births in China. We present a quantitative model where people choose to sex-select because they perceive that married sons are more valuable than married daughters. Due to the predominant patrilocal kinship system in China, daughters-in-law provide valuable emotional and financial support, enhancing the perceived present value of married sons. We argue that inter-generational transfer data will help ascertain the extent to which economic schemes (such as pension plans for families with no sons) can curtail the increasing sex ratio at birth.

    View details for DOI 10.4054/DemRes.2008.19.54

    View details for PubMedID 21113272

    View details for PubMedCentralID PMC2990196

  • Population and prehistory II: Space-limited human populations in constant environments THEORETICAL POPULATION BIOLOGY Puleston, C. O., Tujapurkar, S. 2008; 74 (2): 147-160


    We present a population model to examine the forces that determined the quality and quantity of human life in early agricultural societies where cultivable area is limited. The model is driven by the non-linear and interdependent relationships between the age distribution of a population, its behavior and technology, and the nature of its environment. The common currency in the model is the production of food, on which age-specific rates of birth and death depend. There is a single non-trivial equilibrium population at which productivity balances caloric needs. One of the most powerful controls on equilibrium hunger level is fertility control. Gains against hunger are accompanied by decreases in population size. Increasing worker productivity does increase equilibrium population size but does not improve welfare at equilibrium. As a case study we apply the model to the population of a Polynesian valley before European contact.

    View details for DOI 10.1016/j.tpb.2008.05.007

    View details for Web of Science ID 000259165700001

    View details for PubMedID 18598711

    View details for PubMedCentralID PMC2825579

  • Stage dynamics, period survival, and mortality plateaus AMERICAN NATURALIST Horvitz, C. C., Tuljapurkar, S. 2008; 172 (2): 203-215


    Mortality plateaus at advanced ages have been found in many species, but their biological causes remain unclear. Here, we exploit age-from-stage methods for organisms with stage-structured demography to study cohort dynamics, obtaining age patterns of mortality by weighting one-period stage-specific survivals by expected age-specific stage structure. Cohort dynamics behave as a killed Markov process. Using as examples two African grasses, one pine tree, a temperate forest perennial herb, and a subtropical shrub in a hurricane-driven forest, we illustrate diverse patterns that may emerge. Age-specific mortality always reaches a plateau at advanced ages, but the plateau may be reached rapidly or slowly, and the trajectory may follow positive or negative senescence along the way. In variable environments, birth state influences mortality at early but not late ages, although its effect on the level of survivorship persists. A new parameter micro omega summarizes the risk of mortality averaged over the entire lifetime in a variable environment. Recent aging models for humans that employ nonobservable abstract states of "vitality" are also known to produce diverse trajectories and similar asymptotic behavior. We discuss connections, contrasts, and implications of our results to these models for the study of aging.

    View details for DOI 10.1086/589453

    View details for Web of Science ID 000257986200008

    View details for PubMedID 18616387

  • Senescence rates are determined by ranking on the fast-slow life-history continuum ECOLOGY LETTERS Jones, O. R., Gaillard, J., Tuljapurkar, S., Alho, J. S., Armitage, K. B., Becker, P. H., Bize, P., Brommer, J., Charmantier, A., Charpentier, M., Clutton-Brock, T., Dobson, F. S., Festa-Bianchet, M., Gustafsson, L., Jensen, H., Jones, C. G., Lillandt, B., McCleery, R., Merila, J., Neuhaus, P., Nicoll, M. A., Norris, K., Oli, M. K., Pemberton, J., Pietiainen, H., Ringsby, T. H., Roulin, A., Saether, B., Setchell, J. M., Sheldon, B. C., Thompson, P. M., Weimerskirch, H., Wickings, E. J., Coulson, T. 2008; 11 (7): 664-673


    Comparative analyses of survival senescence by using life tables have identified generalizations including the observation that mammals senesce faster than similar-sized birds. These generalizations have been challenged because of limitations of life-table approaches and the growing appreciation that senescence is more than an increasing probability of death. Without using life tables, we examine senescence rates in annual individual fitness using 20 individual-based data sets of terrestrial vertebrates with contrasting life histories and body size. We find that senescence is widespread in the wild and equally likely to occur in survival and reproduction. Additionally, mammals senesce faster than birds because they have a faster life history for a given body size. By allowing us to disentangle the effects of two major fitness components our methods allow an assessment of the robustness of the prevalent life-table approach. Focusing on one aspect of life history - survival or recruitment - can provide reliable information on overall senescence.

    View details for DOI 10.1111/j.1461-0248.2008.01187.x

    View details for Web of Science ID 000256376900002

    View details for PubMedID 18445028

  • Population and prehistory I: Food-dependent population growth in constant environments THEORETICAL POPULATION BIOLOGY Lee, C. T., Tujapurkar, S. 2008; 73 (4): 473-482


    We present a demographic model that describes the feedbacks between food supply, human mortality and fertility rates, and labor availability in expanding populations, where arable land area is not limiting. This model provides a quantitative framework to describe how environment, technology, and culture interact to influence the fates of preindustrial agricultural populations. We present equilibrium conditions and derive approximations for the equilibrium population growth rate, food availability, and other food-dependent measures of population well-being. We examine how the approximations respond to environmental changes and to human choices, and find that the impact of environmental quality depends upon whether it manifests through agricultural yield or maximum (food-independent) survival rates. Human choices can complement or offset environmental effects: greater labor investments increase both population growth and well-being, and therefore can counteract lower agricultural yield, while fertility control decreases the growth rate but can increase or decrease well-being. Finally we establish equilibrium stability criteria, and argue that the potential for loss of local stability at low population growth rates could have important consequences for populations that suffer significant environmental or demographic shocks.

    View details for DOI 10.1016/j.tpb.2008.03.001

    View details for Web of Science ID 000256996000002

    View details for PubMedID 18439637

  • Longevity can buffer plant and animal populations against changing climatic variability ECOLOGY Morris, W. F., Pfister, C. A., Tuljapurkar, S., Haridas, C. V., Boggs, C. L., Boyce, M. S., Bruna, E. M., Church, D. R., Coulson, T., Doak, D. F., Forsyth, S., Gaillard, J., Horvitz, C. C., Kalisz, S., Kendall, B. E., Knight, T. M., Lee, C. T., Menges, E. S. 2008; 89 (1): 19-25


    Both means and year-to-year variances of climate variables such as temperature and precipitation are predicted to change. However, the potential impact of changing climatic variability on the fate of populations has been largely unexamined. We analyzed multiyear demographic data for 36 plant and animal species with a broad range of life histories and types of environment to ask how sensitive their long-term stochastic population growth rates are likely to be to changes in the means and standard deviations of vital rates (survival, reproduction, growth) in response to changing climate. We quantified responsiveness using elasticities of the long-term population growth rate predicted by stochastic projection matrix models. Short-lived species (insects and annual plants and algae) are predicted to be more strongly (and negatively) affected by increasing vital rate variability relative to longer-lived species (perennial plants, birds, ungulates). Taxonomic affiliation has little power to explain sensitivity to increasing variability once longevity has been taken into account. Our results highlight the potential vulnerability of short-lived species to an increasingly variable climate, but also suggest that problems associated with short-lived undesirable species (agricultural pests, disease vectors, invasive weedy plants) may be exacerbated in regions where climate variability decreases.

    View details for Web of Science ID 000253717200003

    View details for PubMedID 18376542

  • Time, transients and elasticity ECOLOGY LETTERS Haridas, C. V., Tuljapurkar, S. 2007; 10 (12): 1143-1153


    How does life history affects the short-term elasticities of population growth rate? We decompose short-term elasticity as a sum of (i) the effect of the perturbation in rates on the unperturbed population structure and (ii) the effect of the original vital rates on the difference in structure between the original and the perturbed population. We provide exact analytical formulas for these components. In a population at its stable stage distribution (SSD), short-term elasticity is determined mainly by the SSD and reproductive value. In a non-stable population, short-term elasticity depends also on the projection of initial structure on the SSD, equal to population momentum. Non-stable stage structures matter most to elasticity if stages are missing that take time to fill in. We show how the demographic damping rate of the original population determines the rate at which short-term elasticity converges to its limiting values.

    View details for DOI 10.1111/j.1461-0248.2007.01108.x

    View details for Web of Science ID 000250700800004

    View details for PubMedID 17883410

  • Detecting variability in demographic rates: randomization with the Kullback-Leibler distance JOURNAL OF ECOLOGY Al-Khafaji, K., Tuljapurkar, S., Horvitz, C., Koop, A. 2007; 95 (6): 1370-1380
  • Why Men Matter: Mating Patterns Drive Evolution of Human Lifespan PLOS ONE Tuljapurkar, S. D., Puleston, C. O., Gurven, M. D. 2007; 2 (8)


    Evolutionary theory predicts that senescence, a decline in survival rates with age, is the consequence of stronger selection on alleles that affect fertility or mortality earlier rather than later in life. Hamilton quantified this argument by showing that a rare mutation reducing survival is opposed by a selective force that declines with age over reproductive life. He used a female-only demographic model, predicting that female menopause at age ca. 50 yrs should be followed by a sharp increase in mortality, a "wall of death." Human lives obviously do not display such a wall. Explanations of the evolution of lifespan beyond the age of female menopause have proven difficult to describe as explicit genetic models. Here we argue that the inclusion of males and mating patterns extends Hamilton's theory and predicts the pattern of human senescence. We analyze a general two-sex model to show that selection favors survival for as long as men reproduce. Male fertility can only result from matings with fertile females, and we present a range of data showing that males much older than 50 yrs have substantial realized fertility through matings with younger females, a pattern that was likely typical among early humans. Thus old-age male fertility provides a selective force against autosomal deleterious mutations at ages far past female menopause with no sharp upper age limit, eliminating the wall of death. Our findings illustrate the evolutionary importance of males and mating preferences, and show that one-sex demographic models are insufficient to describe the forces that shape human senescence.

    View details for DOI 10.1371/journal.pone.0000785

    View details for Web of Science ID 000207455400002

    View details for PubMedID 17726515

    View details for PubMedCentralID PMC1949148

  • The evolutionary demography of ecological change: Linking trait variation and population growth SCIENCE Pelletier, F., Clutton-Brock, T., Pemberton, J., Tuljapurkar, S., Coulson, T. 2007; 315 (5818): 1571-1574


    Population dynamics and evolutionary change are linked by the fundamental biological processes of birth and death. This means that population growth may correlate with the strength of selection, whereas evolutionary change can leave an ecological signature. We decompose population growth in an age-structured population into contributions from variation in a quantitative trait. We report that the distribution of body sizes within a population of Soay sheep can markedly influence population dynamics, accounting for up to one-fifth of observed population growth. Our results suggest that there is substantial opportunity for evolutionary dynamics to leave an ecological signature and visa versa.

    View details for DOI 10.1126/science.1139024

    View details for Web of Science ID 000244934800051

    View details for PubMedID 17363672

  • Sensitivity of the population growth rate to demographic variability within and between phases of the disturbance cycle ECOLOGY LETTERS Morris, W. F., Tuljapurkar, S., Haridas, C. V., Menges, E. S., Horvitz, C. C., Pfister, C. A. 2006; 9 (12): 1331-1341


    For species in disturbance-prone ecosystems, vital rates (survival, growth and reproduction) often vary both between and within phases of the cycle of disturbance and recovery; some of this variation is imposed by the environment, but some may represent adaptation of the life history to disturbance. Anthropogenic changes may amplify or impede these patterns of variation, and may have positive or negative effects on population growth. Using stochastic population projection matrix models, we develop stochastic elasticities (proportional derivatives of the long-run population growth rate) to gauge the population effects of three types of change in demographic variability (changes in within- and between-disturbance-phase variability and phase-specific changes). Computing these elasticities for five species of disturbance-influenced perennial plants, we pinpoint demographic rates that may reveal adaptation to disturbance, and we demonstrate that species may differ in their responses to different types of changes in demographic variability driven by climate change.

    View details for DOI 10.1111/j.1461-0248.2006.00988.x

    View details for Web of Science ID 000242196900007

    View details for PubMedID 17118007

  • Risky business: Temporal and spatial variation in preindustrial dryland agriculture HUMAN ECOLOGY Lee, C. T., Tuljapurkar, S., Vitousek, P. M. 2006; 34 (6): 739-763
  • From stage to age in variable environments: Life expectancy and survivorship ECOLOGY Tuljapurkar, S., Horvitz, C. C. 2006; 87 (6): 1497-1509


    Stage-based demographic data are now available on many species of plants and some animals, and they often display temporal and spatial variability. We provide exact formulas to compute age-specific life expectancy and survivorship from stage-based data for three models of temporal variability: cycles, serially independent random variation, and a Markov chain. These models provide a comprehensive description of patterns of temporal variation. Our formulas describe the effects of cohort (birth) environmental condition on mortality at all ages, and of the effects on survivorship of environmental variability experienced over the course of life. This paper complements existing methods for time-invariant stage-based data, and adds to the information on population growth and dynamics available from stochastic demography.

    View details for Web of Science ID 000238658400019

    View details for PubMedID 16869426

  • Temporal autocorrelation and stochastic population growth ECOLOGY LETTERS Tuljapurkar, S., Haridas, C. V. 2006; 9 (3): 324-334
  • Temporal autocorrelation and stochastic population growth. Ecology letters Tuljapurkar, S., Haridas, C. V. 2006; 9 (3): 327-337


    How much does environmental autocorrelation matter to the growth of structured populations in real life contexts? Interannual variances in vital rates certainly do, but it has been suggested that between-year correlations may not. We present an analytical approximation to stochastic growth rate for multistate Markovian environments and show that it is accurate by testing it in two empirically based examples. We find that temporal autocorrelation has sizeable effect on growth rates of structured populations, larger in many cases than the effect of interannual variability. Our approximation defines a sensitivity to autocorrelated variability, showing how demographic damping and environmental pattern interact to determine a population's stochastic growth rate.

    View details for PubMedID 16958899

  • Plant-animal interactions in random environments: Habitat-stage elasticity, seed predators, and hurricanes ECOLOGY Horvitz, C. C., Tuljapurkar, S., Pascarella, J. B. 2005; 86 (12): 3312-3322
  • Elasticities in variable environments: Properties and implications AMERICAN NATURALIST Haridas, C. V., Tuljapurkar, S. 2005; 166 (4): 481-495


    Elasticities in stochastic matrix models are used to understand both population and evolutionary dynamics. We examine three such elasticities: stochastic elasticity E(ij)(S) with respect to the (i, j) matrix element, the elasticity E(ij)(S mu) with respect to the mean mu(ij) of the matrix element, and the elasticity E(ij)(S sigma) with respect to the variability sigma(ij) of the matrix element. We show that the stochastic elasticity E(S) does not accurately describe the effect of variability; one should use E(S sigma) and E(S mu). We establish two general properties of these elasticities: a sum rule that connects them and a limit on the sum of the E(S sigma). We discuss the implications of these properties for the analysis of buffering and selection on the average rates versus the variability of rates.

    View details for Web of Science ID 000232270600008

    View details for PubMedID 16224704

  • Future mortality: a bumpy road to Shangri-La? Science of aging knowledge environment : SAGE KE Tuljapurkar, S. 2005; 2005 (14): pe9-?


    Americans are getting fatter, and it is known that increased obesity may increase the risk of death. Olshansky et al. have argued that this increase in obesity will likely slow, or even reverse, increases in life expectancy in the United States and perhaps save U.S. Social Security as a result. We discuss historical changes in the mortality rate and the reasons why other analyses argue that life expectancies will continue to increase. We also discuss the limitations of using single risk factors such as obesity as predictors of mortality risk. Finally, we explore the relation between risk factors and the long-term historical increase in human life expectancy.

    View details for PubMedID 15814821

  • A FORMAL MODEL OF AGE-STRUCTURAL TRANSITIONS Conference on Age-Structural Transitions and their Policy Implications Li, N., Tuljapurkar, S. SPRINGER. 2005: 91–105
  • Random scenario forecasts versus stochastic forecasts INTERNATIONAL STATISTICAL REVIEW Tuljapurkar, S., Lee, R. D., Li, Q. 2004; 72 (2): 185-199
  • Soils, agriculture, and society in precontact Hawai SCIENCE Vitousek, P. M., Ladefoged, T. N., Kirch, P. V., Hartshorn, A. S., Graves, M. W., Hotchkiss, S. C., Tuljapurkar, S., Chadwick, O. A. 2004; 304 (5677): 1665-1669


    Before European contact, Hawai'i supported large human populations in complex societies that were based on multiple pathways of intensive agriculture. We show that soils within a long-abandoned 60-square-kilometer dryland agricultural complex are substantially richer in bases and phosphorus than are those just outside it, and that this enrichment predated the establishment of intensive agriculture. Climate and soil fertility combined to constrain large dryland agricultural systems and the societies they supported to well-defined portions of just the younger islands within the Hawaiian archipelago; societies on the older islands were based on irrigated wetland agriculture. Similar processes may have influenced the dynamics of agricultural intensification across the tropics.

    View details for Web of Science ID 000221934300049

    View details for PubMedID 15192228

  • Demography in the 21st century: Introduction THEORETICAL POPULATION BIOLOGY Tujapurkar, S. 2004; 65 (4): 317-317

    View details for DOI 10.1016/j.tpb.2004.01.002

    View details for Web of Science ID 000221621800001

    View details for PubMedID 15136007

  • Using the Lee-Carter method to forecast mortality for populations with limited data INTERNATIONAL STATISTICAL REVIEW Li, N., Lee, R., Tuljapurkar, S. 2004; 72 (1): 19-36
  • The many growth rates and elasticities of populations in random environments AMERICAN NATURALIST Tuljapurkar, S., Horvitz, C. C., Pascarella, J. B. 2003; 162 (4): 489-502


    Despite considerable interest in the dynamics of populations subject to temporally varying environments, alternate population growth rates and their sensitivities remain incompletely understood. For a Markovian environment, we compare and contrast the meanings of the stochastic growth rate (lambdaS), the growth rate of average population (lambdaM), the growth rate for average transition rates (lambdaA), and the growth rate of an aggregate represented by a megamatrix (shown here to equal lambdaM). We distinguish these growth rates by the averages that define them. We illustrate our results using data on an understory shrub in a hurricane-disturbed landscape, employing a range of hurricane frequencies. We demonstrate important differences among growth rates: lambdaS lambdaM. We show that stochastic elasticity, ESij, and megamatrix elasticity, EMij, describe a complex perturbation of both means and variances of rates by the same proportion. Megamatrix elasticities respond slightly and stochastic elasticities respond strongly to changing the frequency of disturbance in the habitat (in our example, the frequency of hurricanes). The elasticity EAij of lambdaA does not predict changes in the other elasticities. Because ES, although commonly utilized, is difficult to interpret, we introduce elasticities with a more direct interpretation: ESmu for perturbations of means and ESsigma for variances. We argue that a fundamental tool for studying selection pressures in varying environments is the response of growth rate to vital rates in all habitat states.

    View details for Web of Science ID 000186172300009

    View details for PubMedID 14582010

  • Reproductive effort in variable environments, or environmental variation is for the birds ECOLOGY Orzack, S. H., Tuljapurkar, S. 2001; 82 (9): 2659-2665
  • Escape in time: stay young or age gracefully? 1st Alcala International Conference on Mathematical Ecology Tuljapurkar, S., Wiener, P. ELSEVIER SCIENCE BV. 2000: 143–59
  • A universal pattern of mortality decline in the G7 countries NATURE Tuljapurkar, S., Li, N., Boe, C. 2000; 405 (6788): 789-792


    Human lifespan has increased enormously this century. But we remain uncertain about the forces that reduce mortality, and about the cost implications of ageing populations and their associated social burden. The poor understanding of the factors driving mortality decline, and the difficulty of forecasting mortality are due in part to the pronounced irregularity of annual to decadal mortality change. Here we examine mortality over five decades in the G7 countries (Canada, France, Germany, Italy, Japan, UK, US). In every country over this period, mortality at each age has declined exponentially at a roughly constant rate. This trend places a constraint on any theory of society-driven mortality decline, and provides a basis for stochastic mortality forecasting. We find that median forecasts of life expectancy are substantially larger than in existing official forecasts. In terms of the costs of ageing, we forecast values of the dependency ratio (that is, the ratio of people over 65 to working people) in 2050 that are between 6% (UK) and 40% (Japan) higher than official forecasts.

    View details for Web of Science ID 000087620600050

    View details for PubMedID 10866199

  • Validation, probability-weighted priors, and information in stochastic forecasts INTERNATIONAL JOURNAL OF FORECASTING Tuljapurkar, S., Boe, C. 1999; 15 (3): 259-271
  • Population momentum for gradual demographic transitions POPULATION STUDIES-A JOURNAL OF DEMOGRAPHY Li, N., Tuljapurkar, S. 1999; 53 (2): 255-262
  • Uncertain demographic futures and social security finances 110th Annual Meeting of the American-Economic-Association LEE, R., Tuljapurkar, S. AMER ECONOMIC ASSOC. 1998: 237–41
  • Stochastic forecasts for social security Conference on Frontiers in the Economics of Aging LEE, R., Tuljapurkar, S. UNIV CHICAGO PRESS. 1998: 393–420
  • Demographic uncertainty and the stable equivalent population MATHEMATICAL AND COMPUTER MODELLING Tuljapurkar, S., LEE, R. 1997; 26 (6): 39-56
  • Demography - Taking the measure of uncertainty NATURE Tuljapurkar, S. 1997; 387 (6635): 760-761

    View details for Web of Science ID A1997XF14400023

    View details for PubMedID 9194553

  • Death and taxes: Longer life, consumption, and social security DEMOGRAPHY LEE, R., Tuljapurkar, S. 1997; 34 (1): 67-81


    We analyze in three steps the influence of the projected mortality decline on the long run finances of the Social Security System. First, on a theoretical level, mortality decline adds person years of life which are distributed across the life cycle. The interaction of this distribution with the age distribution of labor earnings minus consumption, or of taxes minus benefits, partially determines the corresponding steady state financial consequences of mortality decline. The effect of mortality decline on population growth rates also matters, but is negligible in low mortality populations. Second, examination of past mortality trends in the United States and of international trends in low mortality populations, suggests that mortality will decline faster than foreseen by the Social Security Administration's forecasts. Third, we combine the work of the first two parts in dynamic simulations to examine the implications of mortality decline and of alternative forecasts of mortality for the finances of the social security system. Also, we use stochastic population forecasts to assess the influence of uncertainty about mortality decline on uncertainty about finances; we find that uncertainty about fertility still has more important implications than uncertainty about mortality, contrary to sensitivity tests in the official forecasts.

    View details for Web of Science ID A1997WP31400005

    View details for PubMedID 9074832

  • Response. Science Tuljapurkar, S. 1995; 269 (5221): 148-?

    View details for PubMedID 17789831

  • Disaggregation in population forecasting: do we need it? And how to do it simply. Mathematical population studies Lee, R. D., Carter, L., Tuljapurkar, S. 1995; 5 (3): 217-?


    "We have described a method for reducing the dimensionality of the forecasting problem by parsimoniously modeling the evolution over time of the age schedules of vital rates. This method steers a middle course between forecasting aggregates and forecasting individual age specific rates: we reduce the problem to forecasting a single parameter for fertility and another one for mortality. We have described a number of refinements and extensions of those basic methods, which preserve their underlying structure and simplicity. In particular, we show how one can fit the model more simply, incorporate lower bounds to the forecasts of rates, disaggregate by sex or race, and prepare integrated forecasts of rates for a collection of regions. We also discuss alternate approaches to forecasting the estimated indices of fertility and mortality, including state-space methods. These many versions of the basic method have yielded remarkably similar results." (SUMMARY IN FRE)

    View details for PubMedID 12290947

  • HIGH SEX-RATIOS IN CHINA FUTURE SCIENCE Tuljapurkar, S., Li, N., Feldman, M. W. 1995; 267 (5199): 874-876


    In China in recent years, male live births have exceeded those of females by amounts far greater than those that occur naturally in human populations, a trend with significant demographic consequences. The resulting imbalance in the first-marriage market is estimated to be about 1 million males per year after 2010. These "excess" males were not easily accommodated in models with substantial changes in first-marriage patterns. The current sex ratio at birth has little effect on a couple's probability of having at least one son, so future increases in the sex ratio may well occur, especially given increasing access to sex-selective abortion.

    View details for Web of Science ID A1995QG20700055

    View details for PubMedID 7846529

  • High sex ratio at birth and its consequences. Chinese journal of population science Li, N., Tuljapurkar, S., Feldman, M. 1995; 7 (3): 213-221

    View details for PubMedID 12290857

  • Population growth changes targets for immunization. Population today Tuljapurkar, S., John, A. M. 1995; 23 (1): 5-?

    View details for PubMedID 12319060

  • Stochastic population forecasts for the United States: beyond high, medium, and low. Journal of the American Statistical Association Lee, R. D., Tuljapurkar, S. 1994; 89 (428): 1-?


    "This article presents and implements a new method for making stochastic population forecasts that provide consistent probability intervals. We blend mathematical demography and statistical time series methods to estimate stochastic models of fertility and mortality based on U.S. data back to 1900 and then use the theory of random-matrix products to forecast various demographic measures and their associated probability intervals to the year 2065. Our expected total population sizes agree quite closely with the Census medium projections, and our 95 percent probability intervals are close to the Census high and low scenarios. But Census intervals in 2065 for ages 65+ are nearly three times as broad as ours, and for 85+ are nearly twice as broad. In contrast, our intervals for the total dependency and youth dependency ratios are more than twice as broad as theirs, and our ratio for the elderly dependency ratio is 12 times as great as theirs. These items have major implications for policy, and these contrasting indications of uncertainty clearly show the limitations of the conventional scenario-based methods."

    View details for PubMedID 12155397



    In this paper, we explore the hypothesis that environmental variability favors the evolution of migration. Using the single-locus invasion condition for a novel allele in a variable environment, we derive conditions where increased migration rates between two sites are favored. We find that while there is a strong advantage to migrants entering a resident population with no migration, there is little advantage to migrants entering a population where the residents migrate at a different rate. Instead of an optimal rate of migration, there is a range of favored migration rates. Negative spatial correlation and a population structure including more than two sites accentuate the advantage of migration. Extending this model to include the effects of developmental delay (e.g. seed dormancy or diapause) on the evolution of migration, we find that higher levels of such delay reduce the advantage to migrants.

    View details for Web of Science ID A1994MV13000006

    View details for PubMedID 8145562



    We analyze a stage-structured model of a population that displays variable diapause in a randomly varying environment. The ruggedness of the environment is measured by the extent of random variation in per-capita reproductive success. We show how variable diapause and environmental characteristics affect the population's stochastic growth rate. In rugged unpredictable environments, phenotypes that show some tendency to diapause are found to have a higher growth rate than nondiapausing phenotypes. In harsh rugged environments, some tendency to diapause may be all that permits population persistence. Positive serial autocorrelation causes the optimal diapause fraction to decrease, while negative autocorrelation causes that fraction to increase. The structured model behaves very differently from a scalar model for large diapause fractions even in uncorrelated environments, and in many cases predicts a broad optimum. The difference between models is due to the extreme variability of stage structure in populations subject to even small variability when diapause tendency is high.

    View details for Web of Science ID A1993LF75300001

    View details for PubMedID 8327984



    Demographic dynamics is formally equivalent to the dynamics of a Markov chain, as is true of some nonlinear dynamical systems. Convergence to demographic equilibrium can be studied in terms of convergence in the Markov chain. Tuljapurkar (1982) showed that population entropy (Kolmogorov-Sinai entropy) provides information on the rate of this convergence. This paper begins by considering finite state Markov chains, providing elementary proofs of the relationship between convergence rate and entropy, and discusses in detail the uses and limitations of entropy as a convergence measure; these results also apply to Markovian dynamical systems. Next, new qualitative and quantitative arguments are used to discuss the demographic meaning of entropy. An exact relationship is established giving population entropy in terms of the eigenvalues of the Leslie matrix characteristic equation. Finally, the significance of imprimitive and periodic limits is discussed in relation to population entropy.

    View details for Web of Science ID A1993KN16300003

    View details for PubMedID 8468536



    "The properties and uses of stochastic forecasts are discussed here. For linear stochastic projections, we show how the computation of forecast moments and the statistical distribution of forecasts depend on the multiplicative and autoregressive structure of the dynamics. Both scalar and vector projection methods are discussed, and their similarities are explored. Next we discuss the uses of stochastic forecasts, arguing that it is important to relate forecasts to the specific decision-making criteria of particular forecast users. The example of [the U.S. system of] Social Security is used to show how a dynamic programming approach may be used to explore alternative decisions in a probabilistic context."

    View details for Web of Science ID A1992KE72100007

    View details for PubMedID 12157865



    This paper examines simple age-structured models of childhood disease epidemiology, focusing on nonstationary populations which characterize LDCs. An age-structured model of childhood disease epidemiology for nonstationary populations is formulated which incorporates explicit scaling assumptions with respect both to time and to population density. The static equilibrium properties and the dynamic local stability of the model are analyzed, as are the effects of random variability due to fluctuations in demographic structure. We determine the consequences of population growth rate for: the critical level of immunization needed to eradicate an endemic disease, the transient epidemic period, the return time which measures the stability of departures from epidemiological equilibrium, and the power spectrum of epidemiological fluctuations and combined demographic-epidemiological fluctuations. Growing populations are found to be significantly different from stationary ones in each of these characteristics. The policy implications of these findings are discussed.

    View details for PubMedID 1808755

  • The mathematics of infection. Science Tuljapurkar, S. 1991; 254 (5031): 591-592

    View details for PubMedID 17806979



    Many organisms delay the initiation of reproduction even though such delay is not adaptive in a constant environment. Theoretical arguments in this paper show that delaying reproduction can increase fitness in a sufficiently variable environment. This paper uses stochastic demography to analyze the fluctuating population structure produced by environmental uncertainty. The results explain previously puzzling features of life cycle delays observed in nature, predicting that populations of the same species living in environments of differing harshness can display different life history phenotypes, a number of distinct life history phenotypes can coexist neutrally within a single population, and genetic polymorphisms are easily maintained if heterozygotes have intermediate life history phenotypes.

    View details for Web of Science ID A1990CM07700060

    View details for PubMedID 2300574



    This paper studies sex allocation in an age-structured population of hermaphrodites living in a temporally fluctuating environment. The general condition for the evolutionary stable state (ESS) of allocation is derived for density-independent dynamics. This condition is used to determine the effect on the deterministic ESS of a dependence of survival rates on allocation. It is also used to identify the special conditions under which a stochastic ESS is given by a product rule and show how demographic structure and the correlation structure of vital rates determines the stochastic ESS.

    View details for Web of Science ID A1990CU86900001

    View details for PubMedID 2312342



    This paper concisely reviews the demography of populations with random vital rates, highlights examples and techniques which yield insight into population dynamics, summarizes the state of significant applications of the theory, and points to open problems. The central picture in this theory is of a time-varying but statistically stationary equilibrium for population, sharply distinct from the notions of classical demography. The deepest biological insights from the theory reveal the temporal structure of life histories to be a rich arena for natural selection.

    View details for Web of Science ID A1989AE97100001

    View details for PubMedID 2756495



    A variety of density-dependent population models can be described by nonlinear renewal equations. This paper develops analytical tools for such models to study the sustained population cycles which arise by bifurcation. The results obtained describe explicitly the direction of bifurcation, and the period, form, and dynamic stability of sustained cycles. The results are illustrated by application to a cohort-controlled model of human populations which has been proposed as a formalization of the Easterlin effect.

    View details for Web of Science ID A1987J665700003

    View details for PubMedID 3660273


    View details for Web of Science ID A1986F264400006

    View details for PubMedID 3805912



    This paper studies the dynamics of an age-structured population which experiences cyclical variation in vital rates. The principal features of population behavior are found to be contained in an explicitly calculable response function. Three distinct regimes of qualitative behavior are described when cycle period is respectively much less than, of the order of, and much greater than the average generation length. These results make explicit the way in which transient properties corresponding to average vital rates determine population response to cycles.

    View details for Web of Science ID A1985ARQ7900001

    View details for PubMedID 4060082



    The steady state distribution of age structure is studied for populations with two age classes and stochastic vital rates. For a serially uncorrelated dichotomic vital rate the distribution of age structure is found analytically to be a singular steplike function; outside a specific region of vital rate values the singular function crosses a threshold to a smooth function. For a vital rate following a correlated two state Markov process the joint distributions of age structure and environment are found analytically to be singular steplike functions; again a threshold marks a transition to a smooth function. For fecundities which are serially uncorrelated but continuously distributed the age structure distribution is obtained as a smooth analytic function for all parameter values. These explicit results have applications to studies of age structure and average growth rate.

    View details for Web of Science ID A1984TC88000007

    View details for PubMedID 6470584



    The Hilbert projective metric is applied to the continuous-time Lotka equation in demography to establish weak ergodicity: populations with the same time-varying fecundity and mortality schedules ultimately have the same age composition. The analysis displays clearly the dynamic content of Lotka's equation and identifies a contraction operator which forces convergence of birth sequences over time. The relationship between primitivity in the discrete (Leslie) and continuous (Lotka) demographic models is made clear.

    View details for Web of Science ID A1982NY63500007

    View details for PubMedID 7119584



    By using both numerical and analytical approaches, we have shown that heterosis alone is not a mechanism for maintaining many alleles segregating at a locus. Even when all heterozygous are more fit than all homozygotes, the proportion of fitness arrays that will lead to a stable, feasible equilibrium of more than 6 or 7 alleles is vanishingly small. More alleles can be maintained if, in addition to heterosis, it is assumed that there is very little variation in fitness from heterozygote to heterozygote, with the ratio of mean heterosis to standard deviation of fitness among heterozygotes in the neighborhood of 10. When such conditions hold, the allelic frequency distribution and equilibrium will be very uniform, with all alleles very close to equal frequency (see PDF). It is much more likely that stable equilibria for multiple alleles will be best explained by multiple niche selection.

    View details for Web of Science ID A1978ER32000011

    View details for PubMedID 17248790


    View details for Web of Science ID A1977DK81700006

    View details for PubMedID 886869