Size-dependent fitness trade-offs of foraging in the presence of predators for prey with different growth patterns

Prey species make choices about whether to employ costly predator avoidance behaviors throughout their growth and lifecycle. Here, we explore the effects of prey size at a given age (ontogenetic size) and prey growth on optimal behavior using a dynamic optimization model. Under the assumption that prey experience greatest predation risk at intermediate or large sizes, and that growth is fastest at intermediate or large sizes, we find that prey should generally forage when they are small in size and hide when they are larger due to a critical strategy switching size threshold. But this is dependent both on the mortality risks and on the rate of growth. Higher background mortality rates or lower predator-induced detection costs of foraging reduce the size at which prey switches from foraging to hiding. Rapid initial growth leads to decreased overall survival and a wider range of conditions under which the prey hides from the predator. As a test case, the model is parametrized with data and applied to understand differing risk-reducing behaviors between cannibal and non-cannibal Leptinotarsa decemlineata, Colorado potato beetle, larvae. The model predicts that a wide range of parameter values lead to differing behaviors of cannibals and non-cannibals of the same age due to differences in ontogenetic size. We also see that individuals with swifter early growth switch to hiding at larger sizes but will often have earlier strategy switching times. This increases survival of cannibals to the critical pupation size with the largest increases occurring when the baseline death rate is high. Our findings suggest that ecological factors that affect the rate of growth during development, even if final size is not affected, may have an important role in prey responses to predators.

Automated summary

Prey species make choices on predator avoidance behaviors based on size and growth. Prey generally forage when small and hide when large, depending on mortality risks and growth rates. The model also predicts differences in risk-reducing behaviors between cannibal and non-cannibal larvae.