Identifying critical foraging thresholds for coral reef fishes

Semmler, Robert and Keith, Sally and Graham, Nick and Sanders, Nathan J. (2021) Identifying critical foraging thresholds for coral reef fishes. PhD thesis, Lancaster University.

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Abstract

Foraging behaviour forms the basis for how species interact with one another, affecting not only their own survival, but the overall structure of ecological communities. In this thesis I illustrate the variety of changes in foraging behaviour that are predicted in response to changes in food availability (i.e., bottom-up effects) and evaluate their predictability via optimal foraging theory. I also show the effects of behavioural change and behavioural variation on community structure and ecosystem functional health. Chapter 2 explores the consistency of predicted optimal foraging responses under decreased food availability. Two evaluated factors showed weak moderating effects on predicted responses: predator taxonomy (mammals are more likely to increase their space-use when food decreases) and prey seasonality (predators with seasonally fluctuating food sources are less likely to increase their space-use). Then, I evaluate the species-level and community-level outcomes of bottom-up effects, using coral-feeding butterflyfishes and bleaching-induced coral mortality as a model system. In Chapter 3, I show how bottom-up effects can scale up, from changes in individual behaviour to changes in the structure of interaction networks. In response to substantial coral mortality, coral-feeding fish became consumed increasingly broad diets, weakening their prey preferences. This resulted in significant changes in resource overlap, and substantial rewiring of the consumer-resource interaction network. Chapter 4 focuses on how specialist and generalist butterflyfishes differ in their foraging behaviour (e.g., patch residence time, bite rate) within low-coral areas, and how these differences might affect their survival. Lastly in Chapter 5, I explored inter- and intraspecific variation in foraging behaviour within coral reef herbivores. I determined that there is significant variation in foraging movement within and across functional groups, highlighting potential complementarity in the scale of their functional delivery. This means together these species may contribute more strongly to grazing than either could alone.