Evidence for recent population bottlenecks in northern spotted owls (Strix occidentalis caurina)
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The northern spotted owl (Strix occidentalis caurina) is one of the most controversial threatened subspecies ever listed under the US Endangered Species Act. Despite protection of its remaining forest habitat, recent field studies show continued declines of northern spotted owls. One potential threat to northern spotted owls which has not yet been shown is loss of genetic variation from population bottlenecks. Bottlenecks can increase the probability of mating among related individuals, potentially causing inbreeding depression, and can decrease adaptive potential. Here we report evidence for recent bottlenecks in northern spotted owls using a large genetic dataset (352 individuals and 10 microsatellite loci). The signature of bottlenecks was strongest in the Washington Cascade Mountains, in agreement with field data. Our results provide independent evidence that northern spotted owls have recently declined, and suggest that loss of genetic variation is an emerging threat to the subspecies’ persistence. Reduced effective population size (N e) shown here in addition to field evidence for demographic decline highlights the increasing vulnerability of this bird to extinction.
KeywordsConservation genetics Bottleneck Microsatellites Effective population size Strix occidentalis caurina US Pacific Northwest US Endangered Species Act
We are indebted to the many people who helped with sample collection and logistics in the field, particularly P. Loschl, S. Ackers, R. Anthony, R. Claremont, D. Herter, S. Hopkins, J. Reid, and S. Sovern. We also thank M. Miller, F. Allendorf, D. Tallmon, G. Luikart, and two anonymous reviewers for comments on the manuscript. Funding was provided by the USGS Forest and Rangeland Ecosystem Science Center and the USDA Forest Service Pacific Northwest Research Station. Samples were collected under US Fish and Wildlife Service threatened species permit number TE026280-11 and Oregon State University Animal Care and Use permit number 3091.
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