I use theory, experiment, and natural history to determine what controls the diversity of symbiont communities. My work focuses primarily on the mutualism between the majority of terrestrial plants and mycorrhizal fungi, though I am interested broadly in all types of mutualism.

Honors & Awards

  • JBS Haldane Award, British Ecological Society (2015)

Professional Education

  • Bachelor of Science, University of Illinois at Urbana Champaign (2011)
  • Master of Science, University of Illinois at Urbana Champaign (2011)
  • Doctor of Philosophy, Indiana University (2016)

Stanford Advisors

All Publications

  • Why mutualist partners vary in quality: mutation–selection balance and incentives to cheat in the fig tree–fig wasp mutualism Ecology Letters Jander, C. K., Steidinger, B. S. 2017: 922–32


    Mutualisms between species are ecologically ubiquitous but evolutionarily puzzling. Host discrimination mechanisms that reduce the fitness of uncooperative symbionts can stabilise mutualism against collapse, but also present a paradox - if discrimination is effective, why do uncooperative symbionts persist? Here, we test whether mutations or fitness benefits of cheating best explain the prevalence of uncooperative wasps in the fig tree-fig wasp mutualism. By combining theory with field-collected data we demonstrate that the proportions of pollen-free wasps of strongly discriminating hosts are reached with reasonable mutation rates. In contrast, in weakly discriminating hosts, the required mutation rates, assuming a single locus, are untenably high, but the required cheater advantages fall within expected ranges. We propose that when discrimination is weak, uncooperative symbionts proliferate until they reach the equilibrium proportion that balances costs and benefits of cheating. Our results suggest that mechanisms that resolve the paradox of uncooperative symbionts differ among host species.

    View details for DOI 10.1111/ele.12792

  • Host discrimination in modular mutualisms: a theoretical framework for meta-populations of mutualists and exploiters PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES Steidinger, B. S., Bever, J. D. 2016; 283 (1822)


    Plants in multiple symbioses are exploited by symbionts that consume their resources without providing services. Discriminating hosts are thought to stabilize mutualism by preferentially allocating resources into anatomical structures (modules) where services are generated, with examples of modules including the entire inflorescences of figs and the root nodules of legumes. Modules are often colonized by multiple symbiotic partners, such that exploiters that co-occur with mutualists within mixed modules can share rewards generated by their mutualist competitors. We developed a meta-population model to answer how the population dynamics of mutualists and exploiters change when they interact with hosts with different module occupancies (number of colonists per module) and functionally different patterns of allocation into mixed modules. We find that as module occupancy increases, hosts must increase the magnitude of preferentially allocated resources in order to sustain comparable populations of mutualists. Further, we find that mixed colonization can result in the coexistence of mutualist and exploiter partners, but only when preferential allocation follows a saturating function of the number of mutualists in a module. Finally, using published data from the fig-wasp mutualism as an illustrative example, we derive model predictions that approximate the proportion of exploiter, non-pollinating wasps observed in the field.

    View details for DOI 10.1098/rspb.2015.2428

    View details for Web of Science ID 000368441200019

    View details for PubMedID 26740613

    View details for PubMedCentralID PMC4721098

  • Qualitative differences in tree species distributions along soil chemical gradients give clues to the mechanisms of specialization: why boron may be the most important soil nutrient at Barro Colorado Island NEW PHYTOLOGIST Steidinger, B. 2015; 206 (3): 895-899

    View details for DOI 10.1111/nph.13298

    View details for Web of Science ID 000352802800005

    View details for PubMedID 25627819

  • Variability in potential to exploit different soil organic phosphorus compounds among tropical montane tree species FUNCTIONAL ECOLOGY Steidinger, B. S., Turner, B. L., Corrales, A., Dalling, J. W. 2015; 29 (1): 121-130
  • The Coexistence of Hosts with Different Abilities to Discriminate against Cheater Partners: An Evolutionary Game-Theory Approach AMERICAN NATURALIST Steidinger, B. S., Bever, J. D. 2014; 183 (6): 762-770


    Evolutionary theory predicts that mutualisms based on the reciprocal exchange of costly services should be susceptible to exploitation by cheaters. Consistent with theory, both cheating and discrimination against cheaters are ubiquitous features of mutualisms. Several recent studies have confirmed that host species differ in the extent that they are able to discriminate against cheaters, suggesting that cheating may be stabilized by the existence of susceptible hosts (dubbed "givers"). We use an evolutionary game-theoretical approach to demonstrate how discriminating and giver hosts associating with mutualist and cheater partners can coexist. Discriminators drive the proportion of cheaters below a critical threshold, at which point there is no benefit to investing resources into discrimination. This promotes givers, who benefit from mutualists but allow cheater populations to rebound. We then apply this model to the plant-mycorrhizal mutualism and demonstrate it is one mechanism for generating host-specific responses to mycorrhizal fungal species necessary to generate negative plant-soil feedbacks. Our model makes several falsifiable, qualitative predictions for plant-mycorrhizal population dynamics across gradients of soil phosphorus availability and interhost differences in ability to discriminate. Finally, we suggest applications and limitations of the model with regard to coexistence in specific biological systems.

    View details for DOI 10.1086/675859

    View details for Web of Science ID 000335721700004

    View details for PubMedID 24823820