Behavioural responses allow organisms to persist under environmental change, maintaining viable populations and shaping ecological communities. My thesis contributes to our understanding of the proximate causes and ultimate consequences of
the drivers of behavioural variation, using coral reef fish as a model system. Across four data chapters, I show how multiple aspects of the physical and social environment contribute to variation in the expression of multiple behaviours both between and within
populations across two reef fish families. In Chapter 1, I use meta-analytical techniques to explore inconsistencies in animal
behavioural responses to environmental change across multiple taxa. In this Chapter, I identify that behavioural variation is driven by a combination of ecological and methodological context-dependent factors. Chapter 2 investigates how broad-scale
variation in nutritional resource availability drives behavioural variation in an obligate corallivore. I show the necessity of considering the co-correlation of multiple behaviours, and the trade-offs between different behaviours in understanding behavioural variation between and within both individuals and populations. Chapter 3considers how energy-dependent territorial behaviours can be predicted by the economic defendability of nutritional resources. In this chapter, I provide the first evidence that terrestrial invasive species on remote islands directly impact farmer damselfish territoriality via the disruption of a seabird-derived nutritional pathway.
Finally, in Chapter 4, I create a mathematical model to further test the applicability of economic defendability theory to territoriality. I confront my model with the empirical data in Chapter 3 to show how reef fish territoriality is driven by the complex interplay
between resource availability, competition intensity and individual state. Finally, I utilise the outputs from Chapters 1-4 to place behaviour in an evolutionary context and conceptualise how behaviour can scale up to impact species interactions, community composition and coral reef resilience.