Environmental change makes robust ecological networks fragile.

Giovanni Strona,Kevin D Lafferty

doi:10.1038/ncomms12462

Abstract

Complex ecological networks appear robust to primary extinctions, possibly due to consumers' tendency to specialize on dependable (available and persistent) resources. However, modifications to the conditions under which the network has evolved might alter resource dependability. Here, we ask whether adaptation to historical conditions can increase community robustness, and whether such robustness can protect communities from collapse when conditions change. Using artificial life simulations, we first evolved digital consumer-resource networks that we subsequently subjected to rapid environmental change. We then investigated how empirical host–parasite networks would respond to historical, random and expected extinction sequences. In both the cases, networks were far more robust to historical conditions than new ones, suggesting that new environmental challenges, as expected under global change, might collapse otherwise robust natural ecosystems.

Highlights

Complex ecological networks appear robust to primary extinctions, possibly due to consumers’ tendency to specialize on dependable resources
A similar pattern occurs within local food webs, with host/parasite networks being more robust to rare host removal than to random host removal[7]
As hosts and parasites diversified, host species varied in their vulnerability to extinction, and parasite species varied in their virulence, that is, in the percentage of central processing unit (CPU) cycles subtracted from a host

Summary

Introduction

Complex ecological networks appear robust to primary extinctions, possibly due to consumers’ tendency to specialize on dependable (available and persistent) resources. We investigated how empirical host–parasite networks would respond to historical, random and expected extinction sequences In both the cases, networks were far more robust to historical conditions than new ones, suggesting that new environmental challenges, as expected under global change, might collapse otherwise robust natural ecosystems. Secondary extinctions could trigger even more extinctions up a food chain, unravelling entire ecosystems[3] For this reason, the already appreciable endangered species list might be just the beginning[4]. Evolution should lead to both specialization and robustness to species loss, global change and human activity might change species vulnerabilities[5,6], which could decrease resource–consumer network stability We investigated this hypothesis by contrasting how historical and novel conditions affected parasite assemblage robustness using computer simulations and information from global host–parasite databases. Current host vulnerability to extinction, measured by modern threats (for example, habitat destruction), can differ from historical vulnerability to extinction[9], suggesting that dependable hosts in the past might not be dependable in the future[5,6,10]

Methods

Results

Conclusion