Contrasting determinants of abundance in ancestral and colonized ranges of an invasive brood parasite

OCLC: 48501074 PDF on file: 5878_Hahn.pdf
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Edited by: J. Michael ScottPatricia J. HeglundMichael L. MorrisonJonathan B. Haufler, and William A. Wall


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Avian species distributions are typically regarded as constrained by spatially extensive variables such as climate, habitat, spatial patchiness, and microhabitat attributes. We hypothesized that the distribution of a brood parasite depends as strongly on host distribution patterns as on biophysical factors and examined this hypothesis with respect to the national distribution of the Brown-headed Cowbird (Molothrus ater). We applied a classification and regression (CART) analysis to data from the Breeding Bird Survey (BBS) and the Christmas Bird Count (CBC) and derived hierarchically organized statistical models of the influence of climate and weather, cropping and land use, and host abundance and distribution on the distribution of the Brown-headed Cowbird within the conterminous United States. The model accounted for 47.2% of the variation in cowbird incidence, and host abundance was the top predictor with an R2 of 18.9%. The other predictors identified by the model (crops 15.7%, weather and climate 14.3%, and region 9.6%) fit the ecological profile of this cowbird. We showed that host abundance was independent of these environmental predictors of cowbird distribution. At the regional scale host abundance played a very strong role in determining cowbird abundance in the cowbird?s colonized range east and west of their ancestral range in the Great Plains (26.6%). Crops were not a major predictor for cowbirds in their ancestral range, although they are the most important predictive factor (33%) for the grassland passerines that are the cowbird?s ancestral hosts. Consequently our findings suggest that the distribution of hosts does indeed take precedence over habitat attributes in shaping the cowbird?s distribution at a national scale, within an envelope of constraint set by biophysical factors.
Publication type Book chapter
Publication Subtype Book Chapter
Title Contrasting determinants of abundance in ancestral and colonized ranges of an invasive brood parasite
Year Published 2002
Language English
Publisher Island Press
Publisher location Washington, DC
Contributing office(s) Patuxent Wildlife Research Center
Description xvii, 868
Larger Work Type Book
Larger Work Subtype Other Government Series
Larger Work Title Predicting Species Occurrences : Issues of Accuracy and Scale
First page 219
Last page 228
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