Body size-mediated starvation resistance in an insect predator.

Individual organisms have to endure transient periods of low-food supply with consequences for growth, reproduction and survival. To resist starvation, animals usually store resources in their bodies: the larger the animals are, the more resources they can carry, but the more energy they need to allocate for maintaining bodily functions. It is unclear how survival relates to body size when food is scarce or absent, and how to characterize individual differences in survival within a population. We use a dynamic energy budget (DEB) model to describe food acquisition, subsequent reserve dynamics and allocation of reserve to body maintenance, growth and maturation of an aquatic insect predator, Notonecta maculata. In a DEB context, we can assume that starvation-induced death strikes when the reserve of an organism is depleted to a certain extent. The way reserve dynamics change upon starvation might thereby influence the ability to survive in the absence of food. Moreover, individuals in a starved population do not die at the same time, even though they might be of the same body size with similar life histories. To describe individual differences in starvation resistance, we link the reserve dynamics derived from the DEB model to the general unified threshold model of survival (GUTS). We tested two different special cases within GUTS, individual tolerance (IT) and stochastic death (SD), and three different starvation options for their suitability in representing experimental data on body size-related starvation resistance. The DEB model reproduced laboratory data on the development of juvenile N. maculata under different food conditions well and closely predicted the weight loss of individuals during prolonged starvation. Both the combined IT-model and the combined SD-model closely fit survival for different food conditions including starvation. However, the two models make different predictions for survival under repeated transient starvation periods. Our results suggest that larger N. maculata specimens are able to resist starvation to a greater extent than smaller conspecifics. The DEB model provides a mechanistic explanation for the positive relationship between body size and starvation resistance, and offers testable hypotheses for possible deviations from this general trend.