Quantifying the links between behavioural and ecological variables influencing marine cleaning mutualisms

Species interactions are mediated by animal behaviour, and are fundamental drivers of global diversity. Mutualistic interactions, whereby multiple parties benefit from an interaction, are highly context-dependent and can scale up to affect populations and communities at higher ecological levels. A well-studied example is the marine cleaning mutualism on coral reefs whereby ‘cleaner’ fish feed on ectoparasites that reside on ‘client’ species. Nonetheless, links between mutualistic behaviours, ecological variables, and potential community-level consequences remain unclear. Using Caribbean cleaner gobies Elacatinus lobeli and in situ observations of 25 cleaning stations, we quantify how mutualism-associated behaviours of cleaners and clients can be correlated with multiple local ecological variables (client diversity, cleaner behavioural phenotypes, territorial damselfish aggression, microhabitat structural complexity). Cleaner responsiveness (flight initiation distance) was associated with cleaning behaviours and therefore cleaning strategy. Cleaners showed higher selectivity towards transient over resident clients, with selectivity likely driven by resource partitioning, client identity and service quality. Cleaning behaviours and client diversity were strongly associated, and cleaner selectivity, cleaning station structural complexity (measured as rugosity), and territorial damselfish aggression were associated with cleaner and client behaviours via direct and indirect pathways. We therefore provide a valuable insight into the importance of considering multiple simultaneous, interacting context dependencies in understanding the proximate drivers underlying the functioning of species interactions.