CANCELLED - Persistence and coexistence in variable environments: Leveraging abiotic and biotic variation for ecological restoration and maintaining diversity

Background/Question/Methods

Environmental variability and species interactions are two cornerstones in our longstanding effort to understand species coexistence and the mechanisms that maintain biodiversity. Recently, it has become increasingly evident that these two factors are not independent, but rather that environmental variability mediates species interactions. As such, here we ask: how do direct effects of environmental variability versus indirect effects mediated by species interactions (i.e., competition) alter species persistence and coexistence? We first present a conceptual framework unifying advances in modern coexistence theory and restoration ecology, allowing us to leverage variability to manage single species populations of native or exotic species as well as community diversity. We couple this conceptual framework with species fecundity data from a highly diverse annual understory community in SW Western Australia that spans environmental gradients in canopy cover and soil phosphorus. We apply a recent method for modeling species interactions in diverse ecosystems and across environmental variability (Weiss-Lehman et al. 2022) to compare how abiotic variability, biotic variability, and their joint interaction can modify species persistence using low-density growth rate calculations.

Results/Conclusions

Observed environmental variability in canopy cover and soil phosphorous had direct effects on all focal species’ demography, altering density independent growth rates. In the most extreme case (for the native, Trachymene cyanopetala), density independent growth doubled across the gradient in canopy cover. In parallel, after accounting for underlying environmental variability, we found strong variation in species’ interactions ranging from facilitative to strongly competitive. Incorporating neighborhood stochasticity (i.e., variability in neighboring species’ identities and abundances), however, yielded similar overall net effects across our focal species: a moderately weak competitive neighborhood. Native species tended to experience more variation in the strength of species interactions compared to exotic species. Critically, we found strong evidence of indirect effects of environmental variation; the strength of species’ interactions was mediated by underlying environmental variability in both canopy cover and soil phosphorous. Variability in the environment and species interactions can alter focal species’ low-density growth rates from positive (predicted persistence) to negative (predicted local extinction), informing when—and under what environmental conditions—restoration efforts could result in successful removal of exotics or improved growth rates of natives. Our results highlight the joint impact of abiotic and biotic variation as drivers of species’ demography, species interactions, and coexistence.