THERMOREGULATORY AND BEHAVIORAL RESPONSE OF MOOSE: IS LARGE BODY SIZE AN ADAPTATION OR CONSTRAINT?
The basis of the “Bell-Jarman Principle” is that body size of ruminants is related to both food requirements and digestive capacity. Large herbivores require greater absolute quantities of forage than smaller ones. But smaller herbivores have higher maintenance costs and require higher quality food. Trade-offs between time-energy constraints and food acquisition determine the limitations of each herbivore. The moose (Alces alces) is a particularly interesting herbivore because it is an apparent exception to the “Bell-Jarman Principle”. Numerous bioenergetic, digestive, and morphological forces have shaped the adaptive specializations of moose. The large body size is an adaptation to travel through deep snow, to minimize heat loss in seasonal northern environments, and perhaps to minimize predation. The large body size and effective insulation make the moose extremely cold tolerant by conserving heat and reducing energy requirements during harsh weather. Warm environments favor smaller cervids such as white-tailed deer (Odocoileus virginianus) which dissipate heat rapidly. Heat loading in moose occurs at relatively low ambient temperatures in both winter and summer. The simulation model in this paper summarizes work on bioenergetic, behavior, and digestion in moose. Behavioral patterns were predicted favorably. High temperatures result in a preemption of feeding and a loss of potential energy that could not be recovered the subsequent day. It appears that the enigmatic moose is pressured by the “Bell-Jarman Principle” to remain smaller on an energetic basis, however, other forces require the largest size possible and more precarious budgets.
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