PREDICTING BITE SIZE SELECTION OF MAMMALIAN HERBIVORES: A TEST OF A GENERAL MODEL OF DIET OPTIMIZATION

Lisa A. Shipley¹
Andrew W. Illius²
Kjell Danell³

1Department of Biology, Frostburg State University, Frostburg, MD 21532; 2Division of Biological Sciences, The University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, United Kingdom; 3Department of Animal Ecology, Swedish University of Agricultural Sciences, 90183 Umea, Sweden;

Introduction

The architecture of woody food plants forces herbivores to make compromises in their food choices (Bunnell and Gillingham, 1985; Van Soest, 1994). Rapid rates of dry matter intake can be achieved... This model is based on recent works that detail the mechanics of harvesting and digesting plants and incorporates scaling relationships of parameters with animal size for generality (Illius and Gordon, 1991, 1992; Spalinger and Hobbs, 1992; Shipley et al., 1994).

Methods

We tested the model by conducting a set of experiments in which we offered six species of dormant deciduous trees common to the boreal forests . . .

Results

Twig diameters cropped by these animals were positively correlated with the mode diameter class of the mass and frequency of twigs on the trees (Figure 1). . .

Discussion

We concluded that our model is useful for predicting, a priori, the twig diameters selected by herbivores on dormant deciduous trees. . .

Acknowledgments

The authors wish to acknowledge . . .

Literature Cited

Bunnell, F.L. and M.P. Gillingham. 1985. Foraging behavior: dynamics of eating out. Pp 53-79 In Bioenergetics of Wild Herbivores (Hudson, R.J. and R.G. White, eds.), CRC Press, Boca Raton, FL.

Illius, A.W. and I.J. Gordon. 1991. Prediction of intake and digestion in ruminants by a model of rumen kinetics integrating animal size and plant characteristics. J. Agri. Sci. 116:145-157.

Illius, A.W. and I.J. Gordon. 1992. Modelling the nutritional ecology of ungulate herbivores: evolution of body size and competitive interactions. Oecologia 89:428-434.

Shipley, L.A., J.E. Gross, D.E. Spalinger, N.T. Hobbs, and B.A. Wunder. 1994. The scaling of intake rate in mammalian herbivores. Amer. Nat. 143:1055-1082.

Van Soest, P.J. 1994. Nutritional ecology of the ruminant. Comstock Publications, Ithaca, NY, 476 Pp

Figure 1. Theoretical relationship between twig diameter and daily net energy intake rate of herbivores as subject to constraints on harvesting and digestion/passage.

Figure 2. The twig diameters selected by roe deer, red deer, and moose feeding on six species of deciduous trees in relation to the diameters predicted by the optimal bite size model.