How sharp is the knife? Herbivore and carnivore sensitivity to resource stoichiometric quality

While understanding feeding preferences of herbivores and carnivores is of major importance in ecology, we still know very little on the sensitivity of different functional groups to suboptimal stoichiometric resource quality. Here, we apply concepts of ecological stoichiometry to shed light on differences in the nutritional requirements of herbivores and carnivores, and to make predictions on the influence of suboptimal resource stoichiometric quality on the fitness of these different consumers to. Herbivores generally experience more variation in the quality of their resource than carnivores do, and these differences have likely shaped the extent to which coping mechanisms have evolved. Consequently, we expect 1) herbivores to maintain their stoichiometric homeostasis over a broader range of resource stoichiometry than carnivores, 2) the threshold elemental ratio (TER), i.e. the dietary carbon to nutrient ratio which maximizes fitness, of herbivores to be higher than that of carnivores, 3) a narrower and sharper knife-edge response in carnivores than herbivores and 4) asymmetric knife-edge responses indicating a higher sensitivity to the diet quality that consumers are not used to dealing with, namely nutrient limitation in carnivores and nutrient excess in herbivores. Our study poses that documenting the ranges of resource quality where consumer fitness declines in diverse organisms is a very promising avenue to increase our understanding of community composition and food web functioning.

Automated summary

Understanding the nutritional requirements and sensitivity of herbivores and carnivores to suboptimal resource quality is crucial in ecology. Herbivores are more affected by variations in resource quality than carnivores, leading to differences in coping mechanisms. Our study predicts that herbivores can maintain stoichiometric homeostasis over a broader range of resource stoichiometry compared to carnivores. It also suggests that the threshold elemental ratio and knife-edge response differ between herbivores and carnivores, indicating a higher sensitivity to diet quality in carnivores and herbivores. Documenting the impact of resource quality on consumer fitness can enhance our understanding of community composition and food web functioning.