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The decline of mule deer populations in the Western United States during the
past decade has rapidly become a major source of concern for biologists,
managers, conservationists and hunters. Typical hypotheses to explain these
declines focus on the effects of predators, weather conditions or habitat
modifications. Little discussion is directed to the effects of potential
competitors, yet in large portions of the mule deer range they occupy the same
areas as other ungulates such as white-tailed deer and elk. We evaluated 19
years of aerial surveys for mule and white-tailed deer conducted on the Colville
Indian Reservation from 1982 to 2001 for evidence of competition between these
three populations using a simple discrete time population growth and competition
model. These data provide strong evidence for competition between
metapopulations of these three species of cervids. Our approach provides
estimates of the magnitude of the negative impact of white-tailed deer on mule
deer populations and vice versa. We estimate that the depressive effect of each
species on its own rate of increase is 50% stronger than its effects on
competitors. We explore these questions using both classical inferential
statistics and information theoretic evaluations of competing models.
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