Does plant trait diversity reduce the ability of herbivores to defend against predators? The plant variability–gut acclimation hypothesis

•We propose the plant variability–gut acclimation hypothesis.•Herbivores experience astounding variability in plant defenses and nutrition.•Plant variability requires herbivores to acclimate to changing plant conditions.•Acclimation is costly in terms of time, energy, and nutrients.•The costs of acclimation limit the ability of herbivores to defend against predators.

Variability in plant chemistry has long been believed to suppress populations of insect herbivores by constraining herbivore resource selection behavior in ways that make herbivores more vulnerable to predation. The focus on behavior, however, overlooks the pervasive physiological effects of plant variability on herbivores. Here we propose the plant variability–gut acclimation hypothesis, which posits that plant chemical variability constrains herbivore anti-predator defenses by frequently requiring herbivores to acclimate their guts to changing plant defenses and nutrients. Gut acclimation, including changes to morphology and detoxification enzymes, requires time and nutrients, and we argue these costs will constrain how and when herbivores can mount anti-predator defenses. A consequence of this hypothesis is stronger top-down control of herbivores in heterogeneous plant populations.