Structure of trophic and mutualistic networks across broad environmental gradients.

Ellen A R Welti,Anthony Joern

doi:10.1002/ece3.1371

Abstract

This study aims to understand how inherent ecological network structures of nestedness and modularity vary over large geographic scales with implications for community stability. Bipartite networks from previous research from 68 locations globally were analyzed. Using a meta-analysis approach, we examine relationships between the structure of 22 trophic and 46 mutualistic bipartite networks in response to extensive gradients of temperature and precipitation. Network structures varied significantly across temperature gradients. Trophic networks showed decreasing modularity with increasing variation in temperature within years. Nestedness of mutualistic networks decreased with increasing temperature variability between years. Mean annual precipitation and variability of precipitation were not found to have significant influence on the structure of either trophic or mutualistic networks. By examining changes in ecological networks across large-scale abiotic gradients, this study identifies temperature variability as a potential environmental mediator of community stability. Understanding these relationships contributes to our ability to predict responses of biodiversity to climate change at the community level.

Highlights

Understanding changes in community dynamics along major environmental gradients is a major goal of community ecology
This study investigates the hypothesis that broad-scale environmental conditions are drivers of network structure and explain much variation in community network structure observed at a geographic scale
We document an inherent difference of network structure between trophic and mutualistic networks in response to temperature variation over broad geographic gradients

Summary

Introduction

Understanding changes in community dynamics along major environmental gradients is a major goal of community ecology. Changing species diversity along productivity gradients (Tilman et al 2012), the relationship between food web complexity and stability (Krause et al 2003), variable abiotic conditions and the likelihood of trophic cascades (Laws and Joern 2013), or changes with niche metrics such as diet breadth or overall community stability in response to species diversity (Haddad et al 2011; Pianka 1973, 1966a,b) are all examples of long-standing interest in this context. Ecological gradients may affect community dynamics through limiting species richness (Dyer et al 2007); alternatively, environmental conditions may directly influence species interactions and community stability and species richness. We assess changes in communities over gradients of precipitation and temperature using an ecological network framework (Fig. 1)

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