Ecological opportunity drives individual dietary specialisation in leopards.

Abstract

Individual specialisation, when individuals exploit only a subset of resources utilised by the population, is a widespread phenomenon. It provides the basis for evolutionary diversification and can impact population and community dynamics. Both phenotypic traits and environmental conditions are predicted to influence individual specialisation; however, its adaptive consequences are poorly understood, particularly among large mammalian carnivores that play an important role in shaping ecosystems. We used observations of 2960 kills made by 49 leopards Panthera pardus in the Sabi Sand Game Reserve, South Africa, to quantify the magnitude of individual dietary specialisation in a solitary large carnivore, and to examine the proximate and ultimate drivers of this behaviour. We found evidence of individual specialisation in leopard diet, with respect to both the species and size of prey killed. Males tended to be more specialised than females, likely because they could access a wider range of prey due to larger body size. Similarly, individuals that encountered a greater diversity of prey tended to be more specialised. Our results confirmed that ecological opportunity was a key determinant of individual specialisation; however, contrary to predictions, per capita resource availability (and by extension, intraspecific competition) did not affect the degree of specialisation exhibited by individuals. Surprisingly, dietary specialisation appeared to disadvantage male leopards. Specialist males overlapped with fewer resident females, had fewer cubs born on their home ranges, and had fewer cubs survive to independence on their home ranges than generalist males. This may have resulted from the high degree of environmental stochasticity experienced during our study, as dietary specialisation is expected to advantage individuals more during periods of resource predictability. In summary, we showed that a species usually considered to be a dietary generalist was in fact a heterogenous collection of specialist and generalist individuals. Individual specialisation is typically assumed to be maintained by disruptive and/or fluctuating selection; hence, the somewhat paradoxical coexistence of both in the same population might be explained by a dynamic evolutionary equilibrium that exists between specialists and generalists, in which each benefit under different conditions.