Thesis defence by Marc Holmes (Biology)

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

Anthropogenic global change has important impacts on ecological communities and their constituent populations: altered environmental conditions and demographic perturbations modify community dynamics and put their stability to the test. Building a mechanistic and generalised understanding of these effects is therefore important to generate informed predictions of future scenarios. Here, I employ both modelling (chapters 2 and 4) and experimental (chapters 3 and 5) approaches to investigate, broadly, how changing environmental conditions and variable functional traits impact the stability of competitive communities. I demonstrate that, generally, differences in population responses to combined stressor 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 perturbed populations: including such traits in forecasts of population growth can lead to improved predictive performance (chapter 3). Moreover, adaptation to stressed conditions can improve the resistance of communities to stress as well as allowing recovery. Within larger communities, however, it is not sufficient for populations to be adaptive: they must be similarly-adaptive to other competing populations (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. In some cases, potential for feedbacks between population growth and trait changes arise, leading to more complex system dynamics (chapter 5). In conclusion, this thesis further illustrates the complexity of ecological stability, highlighting the importance of dynamic functional traits and demonstrating that fitness and adaptation need to be framed in both absolute and relative contexts, as populations strive to both persist and coexist.

Mark will present the results of his PhD thesis, conducted in the Biology Department (URBE) under the supervision of Frederik De Laender.

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