Abstract
There is debate among ecologists about whether total habitat area or patch arrangement contributes most to population and/or community responses to fragmented or patchy landscapes. We tested the relative effects of patch area and isolation for predicting bird occurrence in a naturally patchy landscape in the Bear River Mountains of Northern Utah, USA. We selected focal patches (mountain meadows) ranging in elevation from 1,920 to 2,860 m and in size from 0.6 to 182 ha. Breeding birds were sampled in each focal meadow during the summers of 2003 and 2004 using variable-distance point transects. Logistic regression and likelihood-based model selection were used to determine the relationship between likelihood of occurrence of three bird species (Brewer’s sparrow, vesper sparrow, and white-crowned sparrow) and area, isolation, and proximity metrics. We used model weights and model-averaged confidence intervals to assess the importance of each predictor variable. Plots of area versus isolation were used to evaluate complex relationships between the variables. We found that meadow area was the most important variable for explaining occurrence for two species, and that isolation was the most important for the other. We also found that the absolute distance was more appropriate for evaluating isolation responses than was the species-specific proximity metric. Our findings add clarity to the debate between ecologists regarding the relative importance of area and isolation in species responses to patchy landscapes.
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Acknowledgments
This research was funded by the US Forest Service, and supported by the USGS Utah Cooperative Fish and Wildlife Research Unit (cooperators: Utah State University, Utah Division of Wildlife Resources, US Geological Survey, Wildlife Management Institute, and the US Fish and Wildlife Service), and the Utah State University Ecology Center. Clint McCarthy of USFS provided early vision for this project, and was instrumental in creating funding opportunities. Marmot Mountain L.L.C. provided camping gear for use in the field. We thank James A. MacMahon, Andreas Leidolf, and Patricia Crammer for their comments and reviews of thesis drafts, and Drs. Thomas C. Edwards Jr, and David Koons for help with analyses. We also thank our field technicians for their dedication and acceptance of extreme working conditions. Thanks to Jingle Wu for helping to re-frame the discussion and for giving the MS a second chance. This manuscript was much improved thanks to insightful reviews by Drs. John Dunning, Eric Bollinger, A. Joshua Leffler, Helene Wagner and several anonymous referees. All URLs, including those listed for relevant software packages, were checked in November 2007, prior to submission of this article. Floral references follow USDA nomenclature available at http://plants.usda.gov. The use of trade or firm names in this paper is for reader information only and does not imply endorsement by the US Geological Survey of any product or service.
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Wilson, T.L., Johnson, E.J. & Bissonette, J.A. Relative importance of habitat area and isolation for bird occurrence patterns in a naturally patchy landscape. Landscape Ecol 24, 351–360 (2009). https://doi.org/10.1007/s10980-008-9309-5
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DOI: https://doi.org/10.1007/s10980-008-9309-5