The role of environment, dispersal and competition in explaining reduced co-occurrence among related species.

Ben G Weinstein,Juan Luis Parra,Catherine H Graham,Stefan Lötters

doi:10.1371/journal.pone.0185493

Abstract

The composition of ecological assemblages depends on a variety of factors including environmental filtering, biotic interactions and dispersal limitation. By evaluating the phylogenetic pattern of assemblages, we gain insight into the relative contribution of these mechanisms to generating observed assemblages. We address some limitations in the field of community phylogenetics by using simulations, biologically relevant null models, and cost distance analysis to evaluate simultaneous mechanisms leading to observed patterns of co-occurrence. Building from past studies of phylogenetic community structure, we applied our approach to hummingbird assemblages in the Northern Andes. We compared the relationship between relatedness and co-occurrence among predicted assemblages, based on estimates of suitable habitat and dispersal limitation, and observed assemblages. Hummingbird co-occurrence peaked at intermediate relatedness and decreased when a closely-related species was present. This result was most similar to simulations that included simultaneous effects of phylogenetic conservatism and repulsion. In addition, we found older sister taxa were only weakly more separated by geographic barriers, suggesting that time since dispersal is unlikely to be the sole factor influencing co-occurrence of closely related species. Our analysis highlights the role of multiple mechanisms acting simultaneously, and provides a hypothesis for the potential importance of competition at regional scales.

Highlights

The area under the curve (AUC) of these models was high across all individual model types
True Skill Statistic (TSS) scores were more variable across modeling types, the correlation between AUC and TSS scores was high across all models and species (GBM = .0.97, generalized linear models (GLM) = 0.96, maximum entropy (MAXENT) = 0.91), suggesting that our evaluation of model performance was consistent across metrics
The relative roles of environmental filtering, dispersal, and competition in promoting the cooccurrence of related species remains a central focus of biogeography

Summary

Introduction

Niche conservatism can result in cooccurrence of closely related species in local assemblages if conserved traits permit existence in a given environment (i.e environmental filtering)[3]. We used ensemble bioclimatic models based on current species distribution to evaluate environmental tolerances and included a dispersal filter based on elevational barriers between assemblages. Our approach builds from this body of work by 1) explicitly accounting for environment using ensemble bioclimatic models, rather than single variables (as in [28]); 2) focusing on individual species, rather than assemblages, to evaluate phylogenetic structure; 3) moving beyond a dichotomous null-modelling framework that evaluates biotic interactions and environmental as opposing forces; and 4) comparing predictions of relatedness and co-occurrence to simulations built with known patterns of trait evolution.

Results

Conclusion