Abundance transitions in multispecies stochastic Lotka-Volterra

Neutral theories of biodiversity assume that all individuals are functionally identical regardless of the species, whereas symmetrical non-neutral (i.e “niche”) theories forego the assumption of equivalent individuals and distinguish solely between self and non-self interactions. Although species survival in both theories depends on stochasticity, competitive niche overlap in non-neutral theories also affects the species abundance distribution; coexistence and dominance regimes have been observed in both theories in previous works. Using a minimal model of interacting species, we have comprehensively investigated how the species abundance distribution changes between different regimes defined by immigration rate and the niche overlap transitions. We also identify a previously unknown regime where the abundance distribution is multimodal. We show that the transitions between different coexistence regimes is controlled by the balance between the immigration rate and the extinction times of individual species, and show how the species abundance distribution correlates with the species richness. Our results provide a framework for interpreting the discrepancies of abundances in ecological data and inferring the underlying dynamics that shape communities of interacting species.