PhD Oral Defence: Biologging wildlife behaviour and the seasonality of boreal food webs
PhD Oral Defence of Emily Studd, Natural Resource Sciences
The behavioural decision to be active or inactive represents a trade-off between the need to acquire energy and the costs associated with that acquirement. In seasonal environments, the relative costs and gains associated with activity can shift dramatically between winter, when temperatures are cold and resources are scarce, and summer, when temperatures are mild and resources are abundant. Despite the obvious link between activity and seasonality, studies of activity patterns over multi-seasonal time scales are surprisingly sparse, meaning we do not know how activity responds to environmental conditions and, in turn, how activity responses to environmental conditions influence population dynamics and species interactions. In this thesis, I use biologging to quantify how free-ranging animals adjust activity according to seasonal environmental variation, and theoretical modelling to explore the ecological implications of these responses, including population dynamics and trophic interactions. I collected continuous behavioural data through direct observations and biologging technologies over four years on three interacting species - the North American red squirrel, snowshoe hare, and Canada lynx - within the highly seasonal northern boreal forest. After developing novel approaches to recording behaviour over long time periods on free-ranging individuals, I use four years of accelerometry on red squirrels to show that daily activity is the outcome of an optimization of energetic and reproductive gain. Then by integrating behaviour into consumer-resource models, I show how summer-to-winter differences in activity levels determine the seasonality of biomass production and loss, and thus population rates of increase, decrease, and stability. Through empirically-supported theoretical modelling, this thesis highlights the ecological importance of animal activity in seasonal environments, including its bottom-up regulation by environmental conditions and its contributions to populations dynamics and species interactions.