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 organ ization, 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 p rocesses) are hypothesized to scale with body mass (M) for mammalian h erbivores. By using a simple model of processes regulating short-term I, we developed and tested hypotheses on the scaling of these paramete rs 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 si ze scaled with M0.72, whereas cropping time did not scale with body ma ss 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 wa s corroborated by 39 published observations of the maximum I of mammal ian herbivores. Thus, the scaling of I coincides closely with the scal ing of daily energy requirements.