How do herbivorous mammals adjust their trade-off between food and safety?

Abstract

Prey species foraging under a risk of predation have to trade between food acquisition and safety from predation in order to increase their fitness. This trade-off is commonly investigated by studying the trade-off between foraging and vigilance activities. However, vigilance and foraging can be affected by numerous environmental, social, and individual parameters which can also vary seasonally and differ between individuals from the same population. In this context, the overall objective of my PhD was to better understand how herbivorous prey animals manage the feeding/vigilance trade-off at a fine scale, considering the wide range of variables that may affect it, individual variation, and the different functions of vigilance, using female eastern grey kangaroos (Macropus giganteus) and impalas (Aepyceros melampus) as models. I observed that despite the many factors that shape vigilance and feeding rates over short time scales, these behaviours were mainly driven by variation in food resources over longer temporal scales. I also highlighted that predator and social contexts induced different behavioural responses in relation to this trade-off, and that decisions of prey to adjust their vigilance in terms of function and cost were driven by predation risk, food availability, and competition but varied between seasons. Finally, I observed that between-individual variation occurs for this trade-off but that this variation is context dependant. This thesis shows that prey animals constantly adapt their behaviour and strategies according to the situation they experience, in order to balance the acquisition of food and social information with staying safe