Inter-individual variation of behavior in Alpine ibex (Capra ibex): the effect of body size

In mammals body size determines the energy requests, the amount of food can be gathered, the vulnerability to predators, and male reproductive success. Alpine ibex (Capra ibex) is an ungulate characterised by an evident dimorphism between sexes and among males of different ages. Hence, it is an ideal study case to shed light on the effects of body size. While foraging, larger males were less selective than younger and smaller ones, thus suggesting that large body provides to males the possibility to use a poorer quality food, which is more available in the environment. Moreover, larger males were less sensible to predation risk. As a result they had more time for feeding (they were less vigilante) and they fed higher-quality forage (they used riskier and food-rich meadows). However, after wolf recolonization male ibex changed their habitat use in favour of safer low-quality meadows. Finally, old males had higher reproductive success. This was particularly true during rut seasons with abundant snow, when only the tactic successfully used by large males (tending) was adopted. Adult males substantially reduced food intake during the rut having more time to invest in mating activities. In conclusion, the findings of this study showed that the evolution of a large body in male ibex is probably to be favoured because it increases, directly and indirectly, their reproductive success.