Explaining Local-Scale Species Distributions: Relative Contributions of Spatial Autocorrelation and Landscape Heterogeneity for an Avian Assemblage Brady J. Mattsson 1 * ¤a , Elise F. Zipkin 2 , Beth Gardner 3 , Peter J. Blank 2¤b , John R. Sauer 2 , J. Andrew Royle 2 1 Western Ecological Research Center, United States Geological Survey, Sacramento, California, United States of America, 2 Patuxent Wildlife Research Center, United States Geological Survey, Laurel, Maryland, United States of America, 3 Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, North Carolina, United States of America Abstract Understanding interactions between mobile species distributions and landcover characteristics remains an outstanding challenge in ecology. Multiple factors could explain species distributions including endogenous evolutionary traits leading to conspecific clustering and endogenous habitat features that support life history requirements. Birds are a useful taxon for examining hypotheses about the relative importance of these factors among species in a community. We developed a hierarchical Bayes approach to model the relationships between bird species occupancy and local landcover variables accounting for spatial autocorrelation, species similarities, and partial observability. We fit alternative occupancy models to detections of 90 bird species observed during repeat visits to 316 point-counts forming a 400-m grid throughout the Patuxent Wildlife Research Refuge in Maryland, USA. Models with landcover variables performed significantly better than our autologistic and null models, supporting the hypothesis that local landcover heterogeneity is important as an exogenous driver for species distributions. Conspecific clustering alone was a comparatively poor descriptor of local community composition, but there was evidence for spatial autocorrelation in all species. Considerable uncertainty remains whether landcover combined with spatial autocorrelation is most parsimonious for describing bird species distributions at a local scale. Spatial structuring may be weaker at intermediate scales within which dispersal is less frequent, information flows are localized, and landcover types become spatially diversified and therefore exhibit little aggregation. Examining such hypotheses across species assemblages contributes to our understanding of community-level associations with conspecifics and landscape composition. Citation: Mattsson BJ, Zipkin EF, Gardner B, Blank PJ, Sauer JR, et al. (2013) Explaining Local-Scale Species Distributions: Relative Contributions of Spatial Autocorrelation and Landscape Heterogeneity for an Avian Assemblage. PLoS ONE 8(2): e55097. doi:10.1371/journal.pone.0055097 Editor: Ethan P. White, Utah State University, United States of America Received April 18, 2012; Accepted December 19, 2012; Published February 5, 2013 This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. Funding: The authors have no support or funding to report. Competing Interests: The authors have declared that no competing interests exist. * E-mail: brady.mattsson@gmail.com ¤a Current address: Department of Forest- and Soil Sciences, University of Natural Resources and Life Sciences, Vienna, Austria ¤b Current address: Department of Zoology. University of Wisconsin, Madison, Wisconsin, United States of America Introduction Understanding linkages between spatial patterns of biological communities and environmental characteristics is a central question in ecology and natural resource conservation [1–3]. Lichstein et al. [4] distinguished ‘endogenous’ and ‘exogenous’ factors as potential drivers of species distributions, and this typology is useful to articulate hypotheses for interactions between species settlement patterns and their environment. Endogenous factors themselves could be classified as behavioral decisions or evolutionary constraints [4–6]. An important evolutionary con- straint for species distributions is dispersal limitation, which could induce spatial aggregation of species [7–9]. Likewise, a critical behavioral decision for mobile conspecific individuals (henceforth, conspecifics) is whether to aggregate as a strategy to diversify genetic transfers, enhance foraging efficiency, or to gain safety from predators [10,11]. In a heterogeneous environment, these endogenous factors could interact with exogenous factors, which would include particular habitat conditions such as landform, microclimate, and vegetation structure and composition that favor fitness [4–6]. Distinguishing and accounting for these sources of variability in predicting species distributions remains a formidable challenge. There are at least four hypotheses that can explain the distribution patterns of species at a given resolution. First, a null hypothesis is that species are distributed randomly and are therefore equally likely to occur among patches, i.e., spatial units at the scale of an individual home range. With such a random distribution, we would predict that a species occurrence pattern corresponds with neither the condition of patches (e.g., local land cover) nor conspecific occupancy of adjacent patches. Although this null hypothesis contradicts much of modern ecological theory [12,13], this pattern may be more parsimonious if both endogenous and exogenous factors under consideration have only a weak influence. This null hypothesis therefore may serve as a useful baseline for comparison with hypotheses that assume nonrandom species distributions. A second hypothesis is that species are not randomly distributed and that endogenous factors dominate, where the species aggregates such that it is more likely PLOS ONE | www.plosone.org 1 February 2013 | Volume 8 | Issue 2 | e55097