Competition Between Fox (Sciurus Niger) and Gray (S. Carolinensis) Squirrels (Illinois, Habitat Selection, Behavior)
Brown, Bruce Walter
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https://hdl.handle.net/2142/77621
Description
Title
Competition Between Fox (Sciurus Niger) and Gray (S. Carolinensis) Squirrels (Illinois, Habitat Selection, Behavior)
Author(s)
Brown, Bruce Walter
Issue Date
1984
Department of Study
Ecology, Evolution, and Conservation Biology
Discipline
Ecology, Evolution, and Conservation Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Ecology
Language
eng
Abstract
The role of competition in free-living populations of tree squirrels was evaluated by manipulating female fox squirrel numbers and monitoring the response of gray squirrels. Supplemental feeding with native mast was used to determine if food was limiting for squirrel populations in east-central Illinois. Foraging and agonistic behaviors of these two sympatric species were evaluated using captive animals. The presence of mange and an index of internal parasite loads were used to evaluate the effects of parasites on natural squirrel populations. The results of a multivariate analysis of habitat selection suggested that neither species showed a strong response to any particular characteristic of the vegetation or to each other. Adult female fox squirrels were dominant to adult female gray squirrels during the breeding season but not during the non-breeding season. This difference provides a competitive mechanism to account for seasonal movements of gray squirrels. Gray squirrels were more efficient foragers than were fox squirrels, which may be a competitive advantage in the absence of agonistic encounters. Parasites seemed to negatively affect fox squirrel survival and reproduction and the resulting reduction in numbers of fox squirrels might reduce potential interactions, which would facilitate coexistence. Although sample sizes were small, increased survival and reproduction in supplemented woodlots lend support to the idea that food availability limits squirrel densities during some winters. Although a limiting resource (food) and potential competitive mechanisms (different foraging abilities and agonistic behavior) were identified and although some dispersion patterns could be interpreted as the result of competitive interactions, the manipulation of fox squirrels provided no conclusive evidence that densities of either fox or gray squirrels could be explained simply by competition.
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