The social and spatial behaviour of caribou Rangifer tarandus

Webber, Quinn Marshall Richard (2020) The social and spatial behaviour of caribou Rangifer tarandus. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

All animals are social at some point in their life. The causes and consequences of animal social behaviour are widely studied, but the integration of space use and spatial features of the landscape within our understanding of social behaviour is not widely studied. My thesis broadly addresses the role of spatial features of the landscape and individual-level space use traits as potential drivers of emergent social behaviour in caribou (Rangifer tarandus). First, I present a theoretical framework linking social and spatial behaviour within the context of evolutionary and behavioural ecology theory. Next, I assess the relationship between social behaviour and space use across scales, from fine-scale foraging and interactions to coarse-scale examination of how individuals and groups vary social behaviour through space and time. Overall, I found that caribou social behaviour is linked to space use and spatial behaviour in four important ways. First, I found that collective movement was an important predictor for patterns of habitat selection, where caribou tend to select foraging habitat (i.e. lichen) while alone, but to move collectively between foraging patches. Second, despite high home range overlap between caribou, and thus potential to associate, sub-groups of individuals had strong social preference for one another and formed distinct social communities. Third, based on a thirty year dataset of caribou group size, I found that group sizes varied spatially and temporally. In contrast to our expectation, groups decreased in size as a function of increasing population density, while groups tended to be larger in winter compared to summer, presumably as a result of seasonal access to foraging opportunities. Finally, I found that social network strength and habitat specialization were density-dependent, while more social individuals were habitat generalists. However, habitat specialization had a greater effect on fitness, where habitat specialists had higher fitness than habitat generalists, but only at high density. My thesis addresses questions about the relationship between social and spatial behaviour and provides a theoretical framework for future studies to address similar questions. Throughout my thesis I also argue for the integration of various diverse ecological fields, including socioecology, spatial ecology, movement ecology, and conservation biology.

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