Defining shark ecological specialisation: concepts, context, and examples

Sharks are traditionally classified as generalists that use a diverse range of habitats and prey. While this is an accurate description of some species, sharks exhibit a range of resource use strategies that affect their influence on communities. These strategies also influence resilience in the face of environmental and anthropogenic effects. Identifying resource use patterns is critical to understanding sharks in aquatic environments. However, despite the rapid increase in studies focused on measuring the dietary and habitat selection patterns of sharks, discussion on how to define the ecological specialisation of sharks has been limited. This is an impediment to communication and research as definitions of specialisation and how to measure it vary based on context. This review presents a conceptual framework within which to define the specialisation of sharks that can be applied to different environmental scales and goals. We present examples of species with varying degrees of specialisation at large and small scales within the proposed context. The effects of specialisation on population stability are also briefly discussed. Specialists are more sensitive to environmental fluctuations and thus more susceptible to population depletion following environmental changes. Therefore identifying specialised species is key to understanding species vulnerabilities and advancing ecological discussions.