Compensatory mechanisms for ameliorating the fundamental trade-off between predator avoidance and foraging.

Most organisms face the problem of foraging and maintaining growth while avoiding predators. Typical animal responses to predator exposure include reduced feeding, elevated metabolism, and altered development rate, all of which can be beneficial in the presence of predators but detrimental in their absence. How then do animals balance growth and predator avoidance? In a series of field and greenhouse experiments, we document that the tobacco hornworm caterpillar, Manduca sexta, reduced feeding by 30-40% owing to the risk of predation by stink bugs, but developed more rapidly and gained the same mass as unthreatened caterpillars. Assimilation efficiency, extraction of nitrogen from food, and percent body lipid content all increased during the initial phase (1-3 d) of predation risk, indicating that enhanced nutritional physiology allows caterpillars to compensate when threatened. However, we report physiological costs of predation risk, including altered body composition (decreased glycogen) and reductions in assimilation efficiency later in development. Our findings indicate that hornworm caterpillars use temporally dynamic compensatory mechanisms that ameliorate the trade-off between predator avoidance and growth in the short term, deferring costs to a period when they are less vulnerable to predation.