Microscale temperatures affect the incidence and implications of predator-avoidance behavior in monarch caterpillars.

The nonconsumptive effects associated with the predator-avoidance behaviors of potential prey species may commonly be context-dependent. In this study, we examined how temperature differences between the phyllosphere and the ground change the consequences of predator-avoidance dropping behavior in monarch caterpillars. We hypothesized that these consequences change on both diel and seasonal timescales, and that the risk associated with exposure to potentially high ground temperatures is likely to be greater for smaller caterpillars that have less thermal inertia and movement ability. We conducted field experiments to assess the mortality risk associated with dropping to the ground for different-sized caterpillars at a wide range of ground temperatures. We also assess if a caterpillar's probability of dropping in response to a standardized, simulated attack is consistent with adaptive expectations given variation in observed mortality risk under different conditions. We found that the survivorship consequences of dropping depend on both temperature and caterpillar size and that monarch caterpillars show context-dependent predator-avoidance behaviors consistent with changing adaptive expectations across a wide range of temperatures and body sizes. However, we also observed a potentially nonadaptive willingness to drop at high temperatures, consistent with a biological constraint imposed by increased reactivity. These results contribute to a general knowledge gap regarding the context dependence of nonconsumptive effects in nature.