Behavioral asymmetries in a moving hybrid zone |
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Authors: | Pearson Scott F |
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Institution: | College of Forest Resources and Burke Museum, University of Washington,
Seattle, WA 98195, USA |
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Abstract: | Three narrow hybrid zones exist between hermit and Townsend'swarblers in
the Pacific Northwest. Character transition curvessuggest that these zones
are moving and that Townsend's warblershave a selective advantage over hermit
warblers. This studycompares year-to-year return rates, male persistence on
territories,pairing success, pairing patterns, and territory quality of
hermitand Townsend's warblers and their hybrids in the WashingtonCascades
hybrid zone. There was no difference in the year-to-yearreturn rate between
the parental species. Townsend's males weremore successful in maintaining
territories and attracting matesthan hermit males. Among mated pairs there
were few hermit malescompared to females, independently supporting the
inferiorityof hermit males in competition for territories or female mate
choicefor Townsend's-like males. I found no difference in the qualityof
hermit and Townsend's territories; however, in poor habitatsTownsend's males
were more successful at attracting mates, suggestingfemale preference for
Townsend's-like males. In high-qualityhabitats, there was no difference in
pairing success betweenthe parental species. The fitness of hybrids relative
to parentalsaffects the width and movement of the zone. Hybrids were
intermediatein their ability to maintain territories and to attract mates,
whichshould increase the width of the zone and accelerate its movement.Fewer
hybrid males returned to from one year to the next, andamong mated pairs
there were few hybrid females relative tomales, suggesting hybrid
inferiority, which should narrow thehybrid zone and slow its movement. |
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Keywords: | Dendroica occidentalis Dendroica townsendi habitat quality hybridization hybrid zones interspecific competition mate choice pairing patterns return rates |
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