POPULATION DYNAMICS AND ENVIRONMENTAL CHANGE: WHICH FACTORS COMPLICATE PREDICTION AND INFERENCE?

Changes in both the biotic and abiotic environment influence individuals’ physiology, morphology and behaviour and influence key ecological rates underpinning population dynamics. Environmental change is ubiquitous in natural systems and is often multifaceted, as multiple aspects of the climate often change simultaneously and the abundance and traits of species in the community are constantly fluctuating. In this thesis, we study the ecological consequences of environmental changes. We identify fundamental factors complicating our understanding of population dynamics and develop analytical tools to reliably infer, from data, the impacts of environmental change on key biological processes. We present evidence that the impacts of environmental change on population dynamics can be modified by other concurrent environmental changes. Furthermore, the impacts on a focal species will likely be strongly dependent on how the performance of interacting species are affected. We then show that the addition of predators to an environment can cause prey to become more defended against predation, at a cost of reduced population growth. Such growth-defence trade-offs are expected to drive complex population dynamics. We demonstrate that our understanding of community dynamics can be improved by identifying how consumption rates vary with changes in morphological or behavioural traits. We identify feedbacks between species’ trait and abundance dynamics. We then provide evidence that environmental warming can modify the impacts of trait change on species interactions. We inferred that this likely resulted from a modified life history strategy or altered resources allocation to growth rather than defence. Finally, we use simulation studies to assess the reliability of current methods at inferring climate effects on the demography of wild populations. We demonstrate that commonly used approaches perform poorly and also identify a reliable modelling framework. The findings of this work provided quantitative insights into the impacts of environmental change on the processes driving species’ dynamics. It also highlights the role of combined environmental change, trait change and species interaction in complicating the prediction of population dynamics.