title: Resource utilization of sympatric and experimentally allopatric cutthroat trout and Dolly Varden charr.
abstract: Resource utilization by cutthroat trout (CT) and Dolly Varden charr (DV) was studied 8 years after experimental transfers from sympatry had established reproducing allopatric populations in two nearby fishless lakes. Allopatric DV significantly increased their utilization of shallow-dwelling zoobenthos, and increased their vertical distribution in comparison to that in sympatry. In contrast, allopatric CT showed little change in the proportions of major prey types utilized, and, if anything, restricted their vertical distribution in comparison to that in sympatry. The results can be explained by the hypothesis that the resource use of DV is strongly influenced by interspecific competition from CT, whereas CT largely remains unaffected by this interaction. An alternative hypothesis, that lake differences can explain the differences in resource use between sympatry and allopatry, was evaluated by comparing food resource availability and other biotic and abiotic characteristics of the three study lakes. None of these could account for the shift in resource use by DV between sympatry and allopatry, but lake differences may explain why allopatric CT showed a restricted habitat use in comparison with their sympatric donor stock. The results of this whole-lake transfer experiment are consistent with earlier reported field and laboratory studies, and suggest that the aggressive dominance of CT is the most important mechanism by which DV are displaced from littoral and near-surface habitats in sympathy with CT.
authors.affiliation: Department of Biology, Division of Zoology, University of Oslo, Blindern, P.O. Box 1050, N-0316, Oslo 3, Norway.
authors.forename: Kjetil
authors.initials: K
authors.lastname: Hindar
authors.affiliation: Fish Research Division, Directorate for Nature Management, Tungasletta 2, N-7000, Trondheim, Norway.
authors.forename: Bror
authors.initials: B
authors.lastname: Jonsson
authors.affiliation: Institute of Animal Resource Ecology, University of British Columbia, 2204 Main Mall, V6T 1W5, Vancouver, B.C., Canada.
authors.forename: Joyce H
authors.initials: JH
authors.lastname: Andrew
authors.affiliation: Institute of Animal Resource Ecology, University of British Columbia, 2204 Main Mall, V6T 1W5, Vancouver, B.C., Canada.
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Northcote
keywords: Interspecific competition; Niche shift; Prey size selection; Salmo clarki; Salvelinus malma