Macronutrient signature of dietary generalism in an ecologically diverse primate in the wild

A question of considerable importance is why some animals are able to succeed on a wide range of diets while others are more tightly constrained. Theory predicts that generalists should show a flexible response for macronutrient acquisition in the face of ecologically-driven constraint on the nutritional balance of available foods, which in the modelling framework of nutritional geometry has been quantitatively characterized as an “equal distance” regulatory model. This prediction, which has empirical support from several laboratory studies on insects, has not been tested for any generalist animal in the wild, nor for any vertebrate. We performed the first such test, using 281 dawn-to-dusk focal animal observations over three years (2013-2015) of Rhesus macaques monkeys (Macaca mulatta tcheliensis), a primate that is second only to humans in ecological generalism. Results showed, as predicted, that macronutrient regulation conformed closely to the equal distance pattern, and differed ma...