Understanding and predicting responses of ecological communities to perturbations

Abstract

Ecological communities—systems formed by several interacting species—are subject to external perturbations due to changing environmental conditions. Perturbations ranging from antibiotics in microbial communities to warming in coral reefs may displace species abundances or alter community composition. Understanding and predicting how perturbations change these two attributes of ecological communities remains a major challenge in ecology. Indeed, solving this challenge is critical to minimize the harmful impacts of perturbations on the biodiversity and functioning of communities. In this thesis, I introduce new theoretical approaches to understand and predict changes in species abundances and community composition following perturbations and apply these approaches to different empirical communities. In particular, this thesis advances current knowledge in three main ways. In Chapters 2 and 3, we explore Lotka-Volterra population dynamics at equilibrium and demonstrate that subsets of species that can tolerate a larger amount of perturbations on model parameters (i.e., structural perturbations) are more likely to persist. We then show how these theoretical results help us to predict the persistence of different subsets of species in communities of competing herbivores and in microbial communities. In Chapter 4, we again leverage Lotka-Volterra dynamics at equilibrium and show that communities that recover faster from perturbations on abundances tend to tolerate larger amounts of structural perturbations. This theoretical connection between these two indicators allow us to assess a community’s response to perturbations using a single indicator, as we illustrate with microbial communities. Finally, in Chapters 5 and 6, we develop a data-driven approach to infer the sensitivity of species abundances to perturbations under non-equilibrium population dynamics. Using model-generated abundance time series, we demonstrate that our approach captures how both the sensitivity of different species and the contribution of species to whole-community sensitivity change over time. We then apply our approach to rocky intertidal and plankton communities to illustrate how and when different species are more likely to be sensitive to perturbations and to contribute to whole-community sensitivity. By combining theoretical developments with empirical data, this thesis moves us one step closer to a comprehensive and practical theory on the responses of communities and their species to perturbations.