Tractable models for testing theories about natural strategies: foraging behaviour and habitat selection of free-ranging sharks

摘要

Marine and terrestrial environments differ fundamentally in space-time scales of both physical and ecological processes. These differences will have an impact on the animals inhabiting each domain, particularly with respect to their spatial ecology. The behavioural strategies that underpin observed distributions of marine species are therefore important to consider. Comparatively little is known, however, about how wild fishes actually respond to gradients in food supply and temperature, and to potential mates. This paper describes how behavioural theory is being used to elucidate the strategies and tactics of free-ranging sharks in three specific areas of study, namely, foraging on zooplankton, behavioural energetics and sexual segregation. The studies discussed are novel because shark movements were tracked in the wild using electronic tags in relation to simultaneous measurements of prey densities and thermal resources. The results show that filter-feeding (basking shark, Cetorhinus maximus) and predatory (dogfish, Scyliorhinus canicula) sharks have relatively complex behaviour patterns integrally linked to maximizing surplus power, often through making short and longer term 'trade-off', decisions between optimal foraging and thermal habitats. Interestingly, female S. canicula exhibit alternative behavioural strategies compared to males, a difference resulting in spatial segregation by habitat. Sexual segregation in this species occurs primarily as a consequence of male avoidance by females. Studies on free-ranging sharks provide a useful model system for examining how a predator's strategy is shaped by its environment. More theory-based studies of the behavioural processes of sharks are required however, before critical comparisons with other vertebrate predators are possible. suggestions for further research to address this knowledge gap are given