Suburban habitats and their role for birds in the urban–rural habitat network: points of local invasion and extinction?
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Suburban habitats in naturally forested areas present a conundrum in the urban–rural habitat network. Typically, these habitats contain less than half of the native woodland bird species that would exist at these sites if they were not developed. They also contain more total bird species than if these sites were left in a natural state. This apparent contradiction raises the question of “How do suburban habitats function in the urban–rural habitat network?” In this study, we analyze bird distributions on three rural-to-urban gradients in different ecoregions of the United States: Oxford, Ohio; Saint Paul, Minnesota; and Palo Alto, California. All three gradients exhibit similar patterns of extinction of native species followed by invasion of common species and subsequent biotic homogenization with urbanization. This patterning suggests that suburban land uses, those represented by the intermediate levels of development on the gradients, are a point of extirpation for woodland birds as well as an entry point for invasive species into urban systems. Furthermore, there are consistent patterns in the functional characteristics of the bird communities that also shift with intensifying urbanization, providing insight on the possible mechanisms of homogenization and community structure in urban ecosystems including an increase in the number of broods per year, a shift in nesting strategies, a decrease in insectivorous individuals, an increase in granivorous individuals, and a decrease in territoriality. Consequently, it appears that there are specific traits that drive the shift in community composition in response to urban and suburban land use. These results have significant implications for improving understanding of the mechanisms of suburban community ecology and conserving birds in urban habitat networks.
KeywordsUrbanization Suburbanization Biotic homogenization Birds Life history Community functionality Rural–urban gradient
Land cover information was provided by a variety of sources including Stanford University, the City of Palo Alto, and the Jasper Ridge Biological Preserve in California; the City of Oxford and the Department of Geography at Miami University in Ohio; and the Minnesota State Department of Natural Resources in Minnesota. Thanks are in order to the many field assistants who have collected the data for this work. They include (but probably aren’t limited to) Alistair Hobday, Charlie Quinn, John Minturn, Tom Minturn, Joe Reale, Scott Schmidt, Josh Dekan, Sarah Kempke, and Jenn Gillen. Thanks, too, are in order for the undergraduate research programs at Miami University and the University of Minnesota, which supported many of these students in their work. Finally, thanks go to Erica Fleishman, our intellectual muse on all things biological.
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