Heterospecific competition and attraction in grassland bird communities differ with habitat quality

McGuire, S. L. and Nocera, J. J. (2015) Heterospecific competition and attraction in grassland bird communities differ with habitat quality. Community Ecology, 16 (2). pp. 206-2014. ISSN 1585-8553

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Abstract

The behavioral basis for habitat selection has been intensively studied, but comparatively little attention has been paid to how the resultant species assemblages are formed or affected. Further, how habitat quality interacts with behavior during habitat selection needs greater exploration. We sought to identify some of the behavioral interactions influencing the development of bird assemblages in agricultural habitats, which we consider a structurally simple model system. We performed point counts in non-cultivated meadows, intensive agriculture, and non-intensive agriculture areas in the 2011 and 2012 breeding seasons in which we particularly focussed on Bobolink (Dolichonyx oryzivorus), Eastern Meadowlark (Sturnella magna), Field Sparrow (Spizella pusilla), Grasshopper Sparrow (Ammodramus savannarum), Savannah Sparrow (Passerculus sandwichensis), and Vesper Sparrow (Pooecetus gramineus). Using presence-absence matrices and EcoSim software on 2011 census data, we determined where competition was likely to occur, and which species were competing. In 2012, we experimentally tested these relationships by introducing artificial competitors onto sites. We implemented a before-after control-impact study by comparing presence-absence data from 2011 to 2012 and using multinomial logistic regression. We found grassland bird assemblages are structured by interspecific competition or attraction. The experimental introduction of Grasshopper Sparrows resulted in several presence/absence changes, which differed based on habitat quality, by conspecifics and four heterospecifics (especially Bobolinks). We speculate that the response to competitors is actually determined by the relative quality of each habitat type for each species.

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