Climate gradients, and patterns of biodiversity and biotic homogenization in urban residential yards

also increased with distance (p = 0.004, R2 = 0.123; Fig 8E). Nestedness (within the dissimilar- ity index) was little related to distance among towns (p = 030, R2 = 0.017; Fig 8F). The homogenization index among pairs of towns ranged from moderate homogeneity (0.231 in a scale of -1 to +1) to high differentiation (-0.516). Of the 66 pairs of towns, 26 pairs supported homogenization, 39 supported differentiation, and 1 was neutral (S3 Table). The regression between the distance between towns and the homogenization index indicated a dis- tance-related relationship, in which closer towns were more likely to show biotic homogeniza- tion and more distant towns were more likely to have biotic differentiation (p = 0.004; R2 = 0.11; Fig 9). Discussion Distance-decay Land snail populations in residential yards were speciose and displayed an overall distance- decay spatial pattern based on similarity of taxonomic composition; that is, reduced similarity with increasing distance among towns. Distance decay patterns result from a combination of spatial variation in environmental factors, and the dispersal ability and environmental toler- ances of organisms [41]. Distance decay patterns have been observed in a wide variety of organisms [42]; including trees [41], predatory invertebrates [43], and aquatic communities [44, 45]. The most apparent environmental factor that could cause a distance decay pattern in our study system is climatic variation among towns–specifically gradients of westward diminishing rainfall and northward colder winter temperatures. Both rainfall [46–49] and cold

Fig 7. Distance decay relationship, as illustrated by the exponential decay regression of the distance between pairs towns and the corresponding Sørensen similarity of the snail faunas (N = 66). The black line is the regression line and the flanking blue lines are the 95% confidence intervals. https://doi.org/10.1371/journal.pone.0234830.g007 PLOS ONE Diversity patterns of yard-dwelling snails across climate gradients PLOS ONE | https://doi.org/10.1371/journal.pone.0234830 August 28, 2020 11 / 18