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

Abstract

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.

Networking nutrients: How nutrition determines the structure of ecological networks

“…Even protein-rich diets can reduce fitness (Anderson et al, 2020), and Bertrand's rule would suggest that this is upheld for most chemicals (Raubenheimer et al, 2005). Similar patterns have been observed in the responses of organisms to elemental content of food (e.g., knife-edge responses; Meunier et al, 2023).…”

To live free or being a parasite: The optimal foraging behavior may favor the evolution of entomopathogenic nematodes

“…Research focused on measuring the nutritional input of insect hosts can help explain this phenomenon [ 61 ]. Additionally, the concept of the threshold elemental ratio (TER), a well-established tool providing a meaningful index of elemental imbalance between a consumer and its food resource, can be explored to unveil the connection between the physiological attributes of nematodes and the food quantity in the environment, shedding light on the observed life history patterns [ 63 , 64 ].…”