Abstract
Spatial variation in community composition may be driven by a variety of processes, including environmental filtering and dispersal limitation. While work has been conducted on the relative importance of these processes on various taxa and at varying resolutions, tests using high-resolution empirical data across large spatial extents are sparse. Here, we use a dataset on the presence/absence of breeding bird species collected at the 10 km × 10 km scale across the whole of Britain. Pairwise spatial taxonomic and functional beta diversity, and the constituent components of each (turnover and nestedness/richness loss or gain), were calculated alongside two other measures of functional change (mean nearest taxon distance and mean pairwise distance). Predictor variables included climate and land use measures, as well as a measure of elevation, human influence, and habitat diversity. Generalized dissimilarity modeling was used to analyze the contribution of each predictor variable to variation in the different beta diversity metrics. Overall, we found that there was a moderate and unique proportion of the variance explained by geographical distance per se, which could highlight the role of dispersal limitation in community dissimilarity. Climate, land use, and human influence all also contributed to the observed patterns, but a large proportion of the explained variance in beta diversity was shared between these variables and geographical distance. However, both taxonomic nestedness and functional nestedness were uniquely predicted by a combination of land use, human influence, elevation, and climate variables, indicating a key role for environmental filtering. These findings may have important conservation implications in the face of a warming climate and future land use change.
Highlights
Biodiversity is currently facing a multitude of global-scale threats from human activity (Dirzo et al, 2014; McGill et al, 2015)
Analyzing spatial variation in species diversity is a powerful means of assessing the impact of different environmental factors on biodiversity as it provides us with information on what is currently limiting species ranges and occupation of sites
The west of Wales was more similar to the north of England and parts of Scotland than the south of England for total beta diversity and turnover for both taxonomic and functional metrics, representing elevation changes between upland and lowland regions (Figures 3A,B,E,F)
Summary
Biodiversity is currently facing a multitude of global-scale threats from human activity (Dirzo et al, 2014; McGill et al, 2015). Comparing the alpha diversity of two communities separated in space provides a measure of the difference in the number of species between these sites but ignores species replacement/turnover (i.e., a species being extirpated from a site and another species colonizing) and can mask biodiversity change (Gonzalez et al, 2016). It has been argued that the study of these partitions provides insight into the drivers of compositional difference between sites (Baselga and Leprieur, 2015) Nestedness in this context is not ‘true’ nestedness [e.g., as measured by the nestedness metric based on overlap and decreasing fill (NODF)], but rather nestedness resultant dissimilarity that allows for the separation of dissimilarity due to turnover from that of nestedness (Baselga, 2012). We use the term ‘nestedness’ to describe nestedness resultant dissimilarity
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