Network resilience of mutualistic ecosystems and environmental changes: an empirical study.

Ellie Nagaishi,Kazuhiro Takemoto

doi:10.1098/rsos.180706

Abstract

It is theorized that a mutualistic ecosystem's resilience against perturbations (e.g. species extinction) is determined by a single macroscopic parameter (network resilience), calculable from the network. Given that such perturbations occur owing to environmental changes (e.g. climate change and human impact), it has been predicted that mutualistic ecosystems that exist despite extensive environmental changes exhibit higher network resilience; however, such a prediction has not been confirmed using real-world data. Thus, in this study, the effects of climate change velocity and human activities on mutualistic network resilience were investigated. A global dataset of plant–animal mutualistic networks was used, and spatial analysis was performed to examine the effects. Moreover, the potential confounding effects of network size, current climate and altitude were statistically controlled. It was demonstrated that mutualistic network resilience was globally influenced by warming velocity and human impact, in addition to current climate. Specifically, pollination network resilience increased in response to human impact, and seed-dispersal network resilience increased with warming velocity. The effect of environmental changes on network resilience for plants was remarkable. The results confirmed the prediction obtained based on the theory and imply that real-world mutualistic networks have a structure that increases ecosystem resilience against environmental changes. These findings will enhance the understanding of ecosystem resilience.

Highlights

Understanding the dynamics of ecosystems is a significant challenge in ecology [1 –4]
Ecological communities consist of a number of species that are connected via interspecific interactions, such as trophic and mutualistic relationships, and they are represented as networks
The full, best and averaged models in spatial analysis indicated that both plant network resilience and animal network resilience increased with network size

Summary

Introduction

Understanding the dynamics of ecosystems is a significant challenge in ecology [1 –4]. Ecological resilience has long been discussed theoretically [9,10] and is often considered to be related to the probability of species (co)extinction. Species coextinction can be considered a series of complex extinction cascades and is often explained in the context of stochastic processes [11]. Network science enhances the understanding of ecological resilience. Vieira & Almeida-Neto [11] proposed a simple stochastic model for complex species coextinctions in mutualistic networks (e.g. pollination networks and seed-dispersal networks), and they showed that ecological resilience decreases with the level of connectedness (connectance or graph density). Fricke et al [17] extended the stochastic model and found that seed-dispersal networks have an optimal structure that minimizes species coextinction. Using the stochastic model, Schleuning et al [18] showed that mutualistic networks are more sensitive to plant than to animal extinction

Methods

Results

Conclusion