Data from: Temperature dependence of predation stress and the nutritional ecology of a generalist herbivore

Prey at risk of predation may experience stress and respond
physiologically by altering their metabolic rates. Theory predicts that
such physiological changes should alter prey nutrient demands from N-rich
to C-rich macronutrients and shift the balance between maintenance and
growth/reproduction. Theory further suggests that for ectotherms,
temperature stands to exacerbate this stress. Yet, the interactive effects
of predation stress and temperature stress on diet, metabolism, and
survival of ectotherms are not well known. This knowledge gap was
addressed with a laboratory study in which wild juvenile grasshoppers were
collected, assigned to one of three groups, and raised at three different
temperatures. All grasshoppers had access to equal quantities of two diets
composed of opposite carbohydrate:protein ratios. Half of the individuals
in each temperature group were exposed to predation risk cues from spider
predators, while the other half were kept in risk free conditions.
Grasshoppers consumed more carbohydrates when exposed to predation risk,
but consumption favored greater protein intake as temperature increased.
Moreover, the difference in carbohydrate intake between risk cue and risk
free treatments diminished as temperature increased. Furthermore,
variability between individual consumption patterns both within and
between treatments decreased markedly as temperature increased, suggesting
that higher temperatures promote more consistent individual consumption
behaviors. Grasshoppers grew faster and larger as temperature increased,
which translated into higher survival rates at higher temperatures. Warmer
grasshoppers also did not alter their metabolic rates in response to
predation risk cues, in contrast to colder grasshoppers. Digestive
efficiency increased with temperature as well, further indicating that
lower temperatures were much more stressful than higher temperatures for
grasshoppers. The study shows that physiological responses of ectothermic
herbivores to predation stress are highly plastic and temperature
dependent, with higher temperatures promoting increased protein intake,
growth, development, survival, and digestive efficiency relative to colder
temperatures. These findings help to reconcile why dietary responses
(proportion of protein vs. carbohydrate intake) to predation stress may
vary among different prey taxa studied previously.