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Factors limiting moose numbers and their interactions with elk and wolves in the central Rocky Mountains, Canada Hurd, Thomas E.

Abstract

Numbers of moose declined in Banff National Park between the mid-1940's and present. This coincided with increases in abundance of both elk and wolves. To explain the decline, I tested several predictions related to exploitative competition with elk, and apparent competition mediated by wolves. The relationship I found between moose and elk winter pellet abundance was consistent with the inverse density pattern expected if exploitative competition and/or apparent competition were operative. Interactions between the two cervids and a shared food resource - willow - supported several of the key criteria required to demonstrate exploitative competition. The two cervids overlapped in resource use, and use by elk probably reduced resource availability to moose. The large asymmetries in distribution, abundance, diet breadth, diet overlap, and browse utilization provided the conditions necessary for elk to dominate competitive interactions. Interactions between predators (wolf and grizzly bear) and the two cervids revealed the potential for apparent competition where the impact on secondary prey, moose, was greater than on primary prey, elk. Predation rates on radio-collared moose appeared unsustainable. The two forms of "competition" operated at different scales, and appeared additive in their negative effect on moose. Exploitative competition was localized in areas of high elk density and apparent competition (predation) operated throughout the study area. My findings contrast with the usual study of mixed competition-predation systems where the two factors provide a mechanism for coexistence.

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