Cross-scale ecological theory sheds light on the maintenance of biodiversity

TL;DR

This paper develops a new spatial neutral biodiversity theory to predict how species abundance distributions change with scale, revealing limitations of neutrality and quantifying the role of non-neutral processes in maintaining biodiversity.

Contribution

It introduces an analytical framework for scale-dependent abundance distributions and applies it to tropical forests, identifying the need for non-neutral processes at local scales.

Findings

Neutral models fit regional data but not local data.

Quantifies the extent of non-neutral processes needed locally.

Provides a target for future biodiversity models.

Abstract

One of the first successes of neutral ecology was to predict realistically-broad distributions of rare and abundant species. However, it has remained an outstanding theoretical challenge to describe how this distribution of abundances changes with spatial scale, and this gap has hampered attempts to use observed species abundances as a way to quantify what non-neutral processes are needed to fully explain observed patterns. To address this, we introduce a new formulation of spatial neutral biodiversity theory and derive analytical predictions for the way abundance distributions change with scale. For tropical forest data where neutrality has been extensively tested before now, we apply this approach and identify an incompatibility between neutral fits at regional and local scales. We use this approach derive a sharp quantification of what remains to be explained by non-neutral processes at the local scale, setting a quantitative target for more general models for the maintenance of biodiversity.