title: Environmental drivers of variability in population and individual foraging strategies
Creators: name: Trevail, AM
Publisher: name: University of Liverpool Repository
Year: 2020

description: Efficient foraging can offer individuals a key opportunity to maximise fitness, with important consequences for population dynamics, species distributions, and ecosystem processes. The constant quest to minimise costs and maximise resource gains has given rise to a diverse range of movement behaviours among animals, the complexities of which we are continually uncovering as we accumulate more data, advance technology and develop methods. We know that animals typically forage on patchy resources that seldom stay constant in space or time. However, it remains unknown whether the degree of resource patchiness, or resource heterogeneity, can shape the costs and benefits of foraging, thus affecting foraging movements and population dynamics of animals. The overall aims of this study were therefore to use environmental, movement, and reproductive success data to understand how resource heterogeneity can drive individual and population foraging behaviour. We focus on the ecology of black-legged kittiwakes, Rissa tridactyla, which are a model species for such questions. As central place breeders that feed solely at the surface, kittiwakes are sensitive to changes in prey availability within the environment around their colony. Furthermore, kittiwakes have been widely studied as an ecosystem indicator species, and so we can build upon prior knowledge and benefit from a large body of existing data. To determine foraging behaviour I use GPS tracking data from 15 colonies around the UK and Ireland collected during the breeding seasons between 2010 and 2017; totalling 415 individuals and 1567 foraging trips. These tracking data were combined with environmental data to determine foraging habitat selection and variability over a predictable cycle, and to characterise environmental heterogeneity, as a proxy for resource heterogeneity, within the foraging range of kittiwakes at each colony. I compare environmental heterogeneity to foraging dynamics and reproductive success to understand the potential fitness costs and benefits of foraging in heterogeneous environments. Finally, I extend habitat selection functions to quantify individual specialisation in habitat selection between colonies, and to understand whether environmental heterogeneity could shape the diversity of movement behaviours. Studies revealed that habitat selection differed over the 12.4-h tidal cycle; and that environmental heterogeneity was associated with amplified changes in habitat selection, most likely because of greater spatial variability in temporal resource changes. In more heterogeneous environments, kittiwakes undertook longer foraging trips, overlapped more with other individuals, and had lower breeding success, which suggests that there is greater competition between individuals where resources are clustered into patches, at a cost to reproduction. Potentially as a mechanism to reduce competition, individual specialisations in habitat selection were more prevalent in heterogeneous environments. Together, results highlight the importance of local environmental processes in governing behavioural adaptations of predators. Chapters provide novel advances into the ecology of kittiwakes, but also into the drivers of optimal foraging trade-offs and the origins of individual differences in behaviour that are relevant well beyond this species. Overall, the work presented in this thesis demonstrates that environmental heterogeneity can play a key role in shaping foraging movements of individuals, population dynamics, and potentially the diversity of animal behaviour.