FIFTY YEARS OF FOOD AND FORAGING IN MOOSE: LESSONS IN ECOLOGY FROM A MODEL HERBIVORE
Keywords:Alces alces, diet selection, foraging behavior, moose, niche breadth, specialization, population regulation
For more than half a century, biologists have intensively studied food habits and foraging behavior of moose (Alces alces) across their circumpolar range. This focus stems, in part, from the economic, recreational, and ecosystem values of moose, and because they are relatively easy to observe. As a result of this research effort and the relatively simple and intact ecosystems in which they often reside, moose have emerged as a model herbivore through which many key ecological questions have been examined. First, dietary specialization has traditionally been defined solely based on a narrow, realized diet (e.g., obtaining >60% of its diet from 1 plant genus). This definition has not been particularly useful in understanding herbivore adaptations because >99% of mammalian herbivores are thus classified as generalists. Although moose consume a variety of browses across their range, many populations consume 50-99% of their diets from 1 genus (e.g., Salix). Like obligatory herbivores, moose have demonstrated adaptations to the chemistry and morphology of their nearly monospecific diets, which precludes them from eating large amounts of grass and many forbs. New classifications for dietary niche suggest that moose fit on the continuum between facultative specialists and facultative generalists. Second, moose have been the subject of early and influential models predicting foraging behavior based on the tradeoffs between quality and quantity in plants. Subsequent models have predicted the size of stems selected by moose based on the tradeoffs between fast harvesting (large twigs) and quick digestion (small twigs). Because of their size, moose require many hours to harvest food, often selecting large bites as browse density declines. Finally, long-term monitoring of moose populations has provided evidence of how populations and communities are regulated. Low reproductive rates and long-term population trends shaped by moose density and forage availability on Isle Royale suggest a strong bottom-up effect on moose populations. Empirical data and simulation models suggest that moose may shape their own forage supply, influencing their community and their own populations, especially when large predators are scarce. Likewise, predation is the primary factor affecting calf survival and thus moose populations in Alaska, demonstrating the important role of top-down factors. Moose will continue to provide a model for examining ecological questions such as tolerances for plant chemistry, what governs animal movements over landscapes, and reciprocal interactions between predation and reproduction.
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