Bruce A. Wunder

Functional Response of Herbivores in Food‐Concentrated Patches: Tests of a Mechanistic Model

Type II functional responses are frequently observed in herbivores feeding in patches where plants are concentrated in space. We tested a mechanistic model of regulation of intake rate of herbivores foraging in food—concentration patches (Laca and Demment 1992, Spalinger and Hobbs 1992) that accounts for asymptotic, Type II responses. The model is based on the hypothesis that competition between cropping and chewing regulates instataneous intake rate in response to changes in the size of bites obtained by the forager. We tested this hypothesis and examined the ability of our model to account for observations of intake rate of 12 species of mammalian herbivores ranging in body mass over 4 orders of magnitude. We measured short—term intake rates of mammalian herbivores feeding in hand—assembled patches of plants. We varied bite size by changing plant height and density in patches offered to herbivores, and observed dry matter intake rates in response to this variation. Averaged across species, our model acc...

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.

Shifts of thermogenesis in the prairie vole (Microtus ochrogaster)

SummaryThe weight-specific oxygen consumption (

HERBIVORE FUNCTIONAL RESPONSE IN HETEROGENEOUS ENVIRONMENTS: A CONTEST AMONG MODELS

\mathop V\limits^ \bullet _{{\rm O}_2 }

Relative medullary area: A new structural index for estimating urinary concentrating capacity of mammals

) of prairie voles caught in winter is 24% higher at 27.5° C and 29% higher at 7.5° C than that of summer animals, thus affording a higher weight-specific thermogenesis in winter than in summer which may allow tolerance to lower thermal exposures. Coincident with the increase in weight-specific rates of oxygen consumption is a decrease in body weight. When total energetic cost to maintain an animal per unit time is calculated, the cost at 27.5° C is the same for both summer and winter animals. Further, the cost to maintain an animal at 7.5° C is less in winter than in summer. Arguments are presented suggesting that prairie voles compensate for increased weight-specific thermogenesis in winter by lowering body weight. The responses to thermal acclimation are quite different in summer and winter animals, thus implying different sorts of metabolic organization. Acclimation to 5° C effects a 26% increase in

Evaluation of morphological indices and total body electrical conductivity to assess body composition in big brown bats

\mathop V\limits^ \bullet _{{\rm O}_2 }