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Adjustments in compound defensive strategies in response to variation in predation risk

Sirot, Etienne
Animal behaviour 2019 v.147 pp. 53-60
animals, antipredatory behavior, energy balance, environmental factors, foraging, habitats, models, predation, risk, trophic levels
Predation risk varies between populations and fluctuates with time. Using a theoretical approach, I studied how differences in this predation regime may influence allocation to antipredator defence in a foraging prey. I considered a set of two complementary defensive tactics, namely, the possibility for the prey to shorten its activity periods, to reduce exposure to predatory attacks and sacrifice some of its foraging time to vigilance, to get a better chance of escaping when under attack. The model reveals relatively complex behavioural adaptations, with important consequences for the energy balance of the animal. In particular, a hierarchy emerges between the two levels of decisions and, as a consequence, the two types of defensive tactics do not respond in a uniform way to changes in environmental conditions. Animals living in relatively safe habitats are thus expected to devote all their time to foraging and adjust their vigilance to the level of risk they endure, while animals living in more dangerous places are expected to adjust the length of their foraging periods to the prevailing level of risk. If the level of risk varies, the animals will avoid being active during infrequent, or particularly deadly, high-risk periods. If these periods become more frequent, or less dangerous, the animals will be fully active, and adjust their vigilance, during low-risk periods, and only partially active during high-risk periods. Finally, when dangerous periods further increase in length or decrease in intensity, the animals will use all available foraging time, and adjust their vigilance during both low- and high-risk periods to the predation regime. Antipredator strategies must then be perceived as a set of behavioural decisions, not only connected to one another, but also embedded within one another, which mediate energy transfers between three consecutive trophic levels.