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UBC Theses and Dissertations

Foraging ecology of coyotes in the Alaska range Prugh, Laura


Predation strongly affects the dynamics of northern vertebrate communities through direct and indirect pathways. Coyotes are one of the main predators of snowshoe hares, and hare populations are characterized by cyclic fluctuations with peaks every 8-11 years. Northern coyotes rely on hares as their primary food source, but they are also major predators of Dall sheep lambs. I examined the response of coyotes to the snowshoe hare population decline in the Alaska Range from 1999-2002 and evaluated the impact of coyote predation on other species in the vertebrate prey community. I first addressed these issues at the population level and then examined the foraging behavior of individual coyotes and social groups. Snowshoe hare abundance declined 10-fold and had a strong effect on coyote diet composition. The absolute biomass of hares was a good predictor of the amount of carrion, voles, porcupine, and hare in the diet, and coyotes were relatively insensitive to changes in the abundance of alternative prey. Coyote selection for hares and porcupines increased as hare numbers declined, and per-capita consumption of porcupines increased 25-fold. Conversely, voles irrupted and represented 61% of available prey biomass by the end of the hare decline, but coyote selection for voles did not increase. Coyote per-capita consumption of Dall sheep was not affected by sheep or hare abundance. Because coyote predation on alternative prey was not dependent on alternative prey density, it was not a stabilizing influence on the prey community. Coyote numbers declined nearly 2-fold during the snowshoe hare decline, with peak coyote numbers occurring 1½ years after the hare peak. Mortality and emigration increased immediately following the peak in coyote numbers, followed by reproductive failure during the low phase of the hare cycle. Coyote-inflicted mortality on Dall sheep lambs fell 3-fold when coyote reproduction failed. Lamb survival was negatively related to hare abundance, showing a limit cycle with a 2-year time delay. Thus, snowshoe hare abundance indirectly affects Dall sheep populations via a numerical response by coyotes. Diet composition varied among individual coyotes and social groups. The pattern of snowshoe hare consumption by social groups largely mirrored the pattern of hare abundance in space and time, indicating that patchiness in prey abundance may have been the main cause of diet variation among coyote groups. Adult coyotes with higher proportions of hare and vole in their diets and lower proportions of porcupine and carrion had increased chances of surviving the hare decline and remaining in the study area.

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