Niche-Neutral Transition in a Lotka-Volterra Model of Diverse Ecosystems

Niche and neutral theory are two prevailing, yet much debated, ideas in ecology proposed to explain the patterns of biodiversity. Whereas niche theory emphasizes selective differences between species and interspecific interactions in shaping the community, neutral theory supposes functional equivalence between species and points to stochasticity as the primary driver of ecological dynamics. In this work, we draw a bridge between these two opposing theories. Starting from a Lotka-Volterra (LV) model with demographic noise and random symmetric interactions, we analytically derive the stationary species abundance distribution and extract the population statistics. Using these results, we demonstrate the existence of a phase transition between niche and neutral regimes, thus reconciling how neutral-like statistics may arise from a diverse community of species with different traits.