Fowler, Joshua C.Ziegler, ShaunWhitney, Kenneth D.Rudgers, Jennifer A.Miller, Tom E. X.2024-08-222024-08-222024Fowler, J. C., Ziegler, S., Whitney, K. D., Rudgers, J. A., & Miller, T. E. X. (2024). Microbial symbionts buffer hosts from the demographic costs of environmental stochasticity. Ecology Letters, 27(5), e14438. https://doi.org/10.1111/ele.14438https://hdl.handle.net/1911/117683Species' persistence in increasingly variable climates will depend on resilience against the fitness costs of environmental stochasticity. Most organisms host microbiota that shield against stressors. Here, we test the hypothesis that, by limiting exposure to temporally variable stressors, microbial symbionts reduce hosts' demographic variance. We parameterized stochastic population models using data from a 14-year symbiont-removal experiment including seven grass species that host Epichloë fungal endophytes. Results provide novel evidence that symbiotic benefits arise not only through improved mean fitness, but also through dampened inter-annual variance. Hosts with “fast” life-history traits benefited most from symbiont-mediated demographic buffering. Under current climate conditions, contributions of demographic buffering were modest compared to benefits to mean fitness. However, simulations of increased stochasticity amplified benefits of demographic buffering and made it the more important pathway of host–symbiont mutualism. Microbial-mediated variance buffering is likely an important, yet cryptic, mechanism of resilience in an increasingly variable world.engExcept where otherwise noted, this work is licensed under a Creative Commons Attribution (CC BY) license.  Permission to reuse, publish, or reproduce the work beyond the terms of the license or beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.Journal articleMicrobial-symbiontshttps://doi.org/10.1111/ele.14438