The Scaling of Intake Rate in Mammalian Herbivores

The rate of food intake exerts an important influence on many aspects of herbivore ecology, including diet and habitat choices, social organization, and predator avoidance. When food is spatially concentrated, short-term dry matter intake rate (I, g/min) is determined largely by morphology of the mouth and mechanics of food consumption. Morphology (tooth size and jaw musculature) and mechanics (cropping and chewing processes) are hypothesized to scale with body mass (M) for mammalian herbivores. By using a simple model of processes regulating short-term I, we developed and tested hypotheses on the scaling of these parameters in 12 species of mammalian herbivores whose masses ranged from 0.05 kg to 547 kg. Specifically, this model predicts that I is controlled by the size of bite taken, by the time required to crop a bite, and by the rate at which food in the mouth can be processed. Maximum bite size scaled with M0 72, whereas cropping time did not scale with body mass and averaged 0.015 min/bite across species. Food processing in the mouth scaled with M0 70. We concluded that the maximum intake rate of mammalian herbivores will scale closely with M0 71. This conclusion was corroborated by 39 published observations of the maximum I of mammalian herbivores. Thus, the scaling of I coincides closely with the scaling of daily energy requirements.