The cross-scale role of reef fish behaviour in mediating space use and behavioural cascades on coral reefs

Sheppard, Catherine and Keith, Sally and Williams, Gareth and Exton, Dan (2024) The cross-scale role of reef fish behaviour in mediating space use and behavioural cascades on coral reefs. PhD thesis, Lancaster University.

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Abstract

Interspecific interactions play a fundamental role in shaping ecological communities. Whilst the non-consumptive effects of predation on animal behaviour and interspecific interactions are widely studied, the role of aggressive interactions between competitors in behavioural cascades is largely unknown. Using coral reef fish as a model system, I address this significant knowledge gap and improve our understanding of how competitive interactions may drive behavioural cascades across multiple ecological levels and taxa. Firstly, I take a macroecological approach to demonstrate strong links between coral reef benthic state and herbivorous fish functional group co-occurrence and their functional group diversity. Secondly, I demonstrate that between-individual variation in aggressive behaviour by farming damselfish creates a competitive landscape of risk on coral reefs. Thirdly, I identify that competitive risk avoidance between reef fish drives behavioural cascades in other taxa, reducing cleaning rates and client diversity at Pederson’s cleaner shrimp Ancylomenes pedersoni stations. Finally, I demonstrate that intraspecific aggression between territorial farming damselfish can be predicted by familiarity and differences in body size. The results presented in this thesis improve our knowledge of both the driving mechanisms and ultimate consequences of competition to community dynamics and ecosystem function. Furthermore, by drawing links across ecological scales, from between-individual behavioural variation to the macroecology of co-occurrence patterns, my thesis highlights the multiple pathways through which co-occurrence and competition may drive behaviourally mediated cascades throughout ecosystems.