SEASONALITY OF SEXUAL SEGREGATION IN DIMORPHIC DEER: EXTENDING THE GASTROCENTRIC MODEL
We extend our gastrocentric model for sexual segregation in dimorphic deer (Cervidae) to include seasonal metabolism of energy and protein in reproductive female, nonreproductive female, and male reindeer and caribou (Rangifer tarandus). We define sexual segregation as the differential use of space by the sexes of animals outside the mating season. Minimum density of energy and protein in the diet is predicted to favor sexual segregation in late winter and summer, but not during autumn. Demands for energy during gestation and for energy and protein during lactation increase dietary minima for reproductive females above levels required by nonreproductive females and males. Projections of gross energy and total protein in diets based on estimated metabolizabilities for males and nonreproductive females predicted that males could subsist on the lowest-quality diets during summer. Projections of minimal dietary content of gross energy indicated that reproductive females probably would feed longer than nonreproductive females and males during summer, as suggested by field observations. Differences in feeding activity between the sexes may be a consequence of metabolic demands and, therefore, and outcome of sexual segregation rather than its cause. The gastrocentric model provides and explanation of behavioral ecology of deer with physiological data for 1 species. Further integration of these disciplines may predict the consequences of size and sex on niche partitioning in relation to environmental changes in forage quality and quantity. Nonetheless, simplistic models are only as valid as data upon which they are constructed. Our model indicated the dire need for studies of diet selection and nutritional physiology in the context of both reproductive status and seasonal demands for both sexes of cervids.
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