A complex speciation-richness relationship in a simple neutral model

TL;DR

This study uses network theory to model speciation and biodiversity in community networks, revealing complex relationships influenced by spatial structure and dispersal, including a transition from negative to positive correlations.

Contribution

It introduces a novel framework combining neutral models with network theory to analyze speciation and richness relationships in spatially structured communities.

Findings

Speciation is more common in isolated communities.

Local richness is higher in more connected communities.

A transition from negative to positive speciation-richness relationship occurs under low dispersal.

Abstract

Speciation is the "elephant in the room" of community ecology. As the ultimate source of biodiversity, its integration in ecology's theoretical corpus is necessary to understand community assembly. Yet, speciation is often completely ignored or stripped of its spatial dimension. Recent approaches based on network theory have allowed ecologists to effectively model complex landscapes. In this study, we use this framework to model allopatric and parapatric speciation in networks of communities and focus on the relationship between speciation, richness, and the spatial structure of communities. We find a strong opposition between speciation and local richness, with speciation being more common in isolated communities and local richness being higher in more connected communities. Unlike previous models, we also find a transition to a positive relationship between speciation and local richness when dispersal is low and the number of communities is small. Also, we use several measures of centrality to characterize the effect of network structure on diversity. The degree, the simplest measure of centrality, is found to be the best predictor of local richness and speciation, although it loses some of its predictive power as connectivity grows. Our framework shows how a simple neutral model can be combined with network theory to reveal complex relationships between speciation, richness, and the spatial organization of populations.