COS 66-1 - Plant diversity shapes populations persistence and stable coexistence in competitive systems

Abstract: Biodiversity maintenance is the core of most biological studies at global, regional, ecosystem, and community scales. Theory and empirical studies show that high levels of diversity can promote community productivity and stability. There is a growing line of evidence that community diversity can impact demographic processes. However, our understanding of diversity influence on population dynamics is limited. Biotic factors like competition by structuring community-level diversity can mediate the effects of diversity on population processes. Still, demographic studies tend to examine the influence of density-dependence with limited attention to how interspecific competition can shape population dynamics. Our study investigates the mediating role of interspecific competition on the influence of community-level diversity on focal species persistence using the Lotka-Volterra competition model. We examine how diversity by altering competitive abilities affects population size and stable coexistence conditions. Moreover, we explore how time-varying phylogenetic relatedness within the community can influence competitive asymmetry and its consequences for focal species population dynamics. We developed a Lotka-Volterra competition model to capture the dynamics of a focal species via the first equation. In contrast, the second equation captures the dynamics of the remaining species in the community. We incorporated the influence of species richness and phylogenetic diversity into the model as nonlinear functions of competitive ability. In a second model, we added an equation to capture the temporal variation of phylogenetic and species diversity. We used qualitative analysis and parameters simulation to explore the impact of diversity on focal species persistence and stable coexistence conditions. We showed that the focal species dynamics become very sensitive to interspecific competition with a slight increase in species richness. As community diversity increases, the effect of species competition effect on the focal species population size reaches its maximum and stabilizes. However, the focal species is more likely to be excluded when closely related to its neighbors. The focal species population tends to persist steadily for a significant change in species composition. Stable coexistence is less expected when diversity is highest, and this is context dependent. Our findings reveal that the influence of community diversity on plant demography is mechanistically mediated by interspecific competition. This highlights the importance of linking community processes, including phylogenetic patterns, to population performance. Additional insights can be drawn for restoration, species reintroduction, invasion, and conservation efforts toward diversity preservation.