Species coexistence as an emergent effect of interacting mechanisms

Although extensively studied, the maintenance of biodiversity remains a highly debated and investigated topic of contemporary research in ecology. Several studies have quantified the contributions of various coexistence mechanisms to biodiversity. However, often stochastic individual-level interactions are abstracted away, or mechanisms are studied in isolation. The intertwined nature and reciprocal influences between mechanisms, as they arise from individual-level interactions, are therefore rarely considered. We propose a novel mechanistic simulation model grounded in neutral theory to capture and quantify emergent effects arising from such mechanism interactions. Three coexistence mechanisms are supported: storage effect, intransitivity, and resource partitioning. We show that basic neutral dynamics and related models of isolated mechanisms can be replicated. Beyond that, we observe difficult to predict, yet significant emergent effects for mechanism combinations. In some cases, coexistence times could be extended more than tenfold compared to the individual mechanisms' performances. Our findings suggest that studies of individual coexistence mechanisms might be insufficient and indeed misleading for quantifying their overall impact on biodiversity. The particular combination of mechanisms and their interactions appear to be of vital importance.