# Fluctuating Growth Rates Link Turnover and Unevenness in Species‐Rich Communities

## TL;DR

The paper explains how environmental randomness and competition shape diversity and species turnover in rich communities.

## Contribution

A minimal model links fluctuating growth rates to unevenness and turnover in species-rich communities.

## Key findings

- Fluctuations in growth rates lead to increasing unevenness and species extinctions.
- Self-limitation and dispersal help maintain species-rich states.
- Species abundance distributions vary systematically in a Buffering–Stabilisation parameter plane.

## Abstract

The maintenance of diversity, the ‘commonness of rarity’, and compositional turnover are ubiquitous features of species‐rich communities. Through a minimal model, we consider how these features reflect the interplay between environmental stochasticity, intra‐ and interspecific competition, and dispersal. We show that, even if species have the same time‐average fitness, fluctuations tend to drive the community towards ever‐growing unevenness and species extinctions, but self‐limitation and/or dispersal allow species‐rich states to be sustained. Species abundance–distributions vary systematically in a Buffering–Stabilisation parameter plane that describes the relative strength of the underlying ecological processes, and cover different empirically relevant power‐law and unimodal shapes. A model describing the effective dynamics of a focal species relates static abundance distributions with turnover dynamics, also when species have different mean fitness. The model suggests how community statistics and time series of individual species can inform on the relative importance of the ecological processes that structure diversity.

Through a minimal model of ecological community dynamics, we explain how the interplay between environmental stochasticity, intra‐ and interspecific competition and dispersal relates to the maintenance of diversity, the commonness of rarity and compositional turnover. In particular, species abundance–distributions vary systematically in a Buffering–Stabilisation parameter plane, spanning different empirically relevant power‐law and unimodal shapes.