Environmental heterogeneity promotes coexistence among plant life-history strategies through stabilizing mechanisms in space and time

Abstract

Spatiotemporal environmental heterogeneity can promote species coexistence through stabilizing mechanisms such as the storage effect. These mechanisms require low density advantages and species-specific responses to heterogeneity. Theory based on organisms, which are short-lived and capitalize beneficial patches instantaneously, suggests that in the presence of spatiotemporal heterogeneity, stabilizing mechanisms should arise more commonly in space than in time.We used an individual-based model to investigate if spatiotemporal soil water heterogeneity promotes stable coexistence among annual and perennial plant life-history strategies, and which functional traits explain the requirements. Scenarios explicitly differed in the resource benefits offered by the range of soil water used to simulate heterogeneity.Our results show that spatiotemporal heterogeneity promoted stable coexistence solely among perennial life-history strategies. Perennial life form delayed population responses to heterogeneity, which resulted in population decoupling among life-history strategies in time as well as in space. Recovery from low density could be explained by a combination of one classical trait which stores the effects of favorable environmental conditions (longevity) and, unexpectedly, a fast resource acquisition strategy evidenced by high adult growth rate and short-term dormancy. Life-history strategy-specific responses emerged from functional differences in seedling competitive ability and seed dispersal distance alone or, additionally, from differences in the hydrological niche. Interestingly, life-history strategies which functionally differed only in dispersal distance coexisted irrespective of whether they experienced a difference in resource benefits themselves or coexisted with life-history strategies experiencing this difference.We show that spatiotemporal heterogeneity in a single abiotic factor promoted stable coexistence through stabilizing mechanisms. Our study highlights the need to study stabilizing mechanisms across different life-history strategies to better understand the effectiveness and dimensions of spatiotemporal heterogeneity in promoting coexistence.