Soutenance publique de thèse de doctorat en Sciences biologiques - Mark HOLMES

Persistence, Coexistence, and Adaptation: The Stability of Competitive Communities Subject to Environmental Change

Jury

• Prof. Patrick KESTEMONT (département de biologie, UNamur), président
• Prof. Frederik DE LAENDER (département de biologie, UNamur), promoteur et secrétaire
• Prof. Frédéric SILVESTRE (département de biologie, UNamur)
• Prof. Sofia VAN MOORSEL (departement of geography, University of Zürich)
  
• Dr Anita NARWANI (department aquatic ecology, EAWAG)
  
• Dr Elisa THEBAULT (institut d’écologie et des sciences de l’environnement, UPMC)

Abstract

Anthropogenic global change has important impacts on ecological communities and their constituent populations as altered environmental conditions and demographic perturbations modify community dynamics and put their stability to the test. It is imperative that we have a mechanistic understanding of the effects of stressors and perturbations and that we are able to generate mechanistically-informed predictions and hypotheses. I employ both modelling (chapters 2 and 4) and experimental (chapters 3 and 5) approaches to broadly investigate how the stability of competitive communities varies as a result of environmental change and variable functional traits. I demonstrate that, broadly speaking, differences in population responses to combined stressor effects impacts diversity loss while the average stressor effect drives loss of functioning/biomass (chapter 2). Dynamic functional traits further influence the long-term stability of populations and including functional traits in forecasts of population growth can lead to improved model performance, exceeding density-dependence in its predictive capacity (chapter 3). Adaptation to stressed conditions can improve the resistance of communities to stress as well as allowing recovery but, within larger communities, it is not sufficient for a population to be adaptive, but it must be similarly adaptive to other competing populations to persist (chapter 4). Finally, trait-mediated growth is dependent on the type of model system being considered as well as how directly-linked the functional traits are to organismal fitness and, in cases, there exists potential for feedbacks between population growth and trait changes to complicate dynamics (chapter 5). In conclusion, this thesis further illustrates the complexity of ecological stability, and highlights that fitness and adaptation need to be framed in both absolute and relative contexts, as populations strive to persist and coexist.

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