Fluctuation-Dependent Coexistence of Stage-Structured Species

AbstractModern coexistence theory is a dominant framework for understanding how environmental fluctuations promote species coexistence. However, assessing fluctuation-dependent mechanisms of coexistence in empirical systems-in which species have diverse life histories and environment-competition relationships-has remained challenging for many ecologists. To help empiricists and theoreticians alike build intuition for the role of fluctuation-dependent mechanisms across systems and environments, we explore how two stage-structured life histories-perennial and seedbanking annuals-differ in competition with a nonseedbanking annual across three environmental scenarios. Our scenarios delineate how species partition resources within and among years and whether competition is most intense during favorable or unfavorable periods. We use this work to link differences in vital rates and interaction strengths to patterns and mechanisms of coexistence. Fluctuation-dependent mechanisms of coexistence can be equally important for perennial species with an adult "storage" stage as for seedbanking annuals. However, coexistence outcomes differentiate between these two stage-structured strategies based on whether they experience stronger or weaker competition in favorable environments. This work sets the stage for applying coexistence theory and fluctuation-dependent partitioning frameworks to perennial and mixed stage-structure communities, facilitating understanding of how environmental variation drives species dynamics across a broader range of systems.