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

Variation in snail assemblage composition among towns was explained by both annual rainfall (DistLM: R2 = 0.257; Table 1) and coldest mean monthly temperature (R2 = 0.379). Together, rainfall and cold temperature explained 50.1% of the variation in taxonomic compo- sition among towns. Snail species typical of yards in each town (based on SIMPER analysis; Fig 6) range from species that are abundant in all towns (i.e., Hawaiia minuscula and Zonitoides arboreus) to spe- cies that are typical of only a single town (i.e., Mesodon thyroides, Xylotrema fosteri, Polygyra cereolus, Gastrocopta procera, and Gastrocopta pellucida). Patterns of typical species vary in the N-S, E-W gradients. For example, Vallonia spp. are typical of only the northern (Kansas) tier of towns, Gastrocopta cristata was a typical species in only the western towns, and Ventridens demissus was abundant in the mid to southeastern sites. Excluding Hawaiia minuscula and Zonitoides arboreus (typical of all 12 towns), distributions of typical species were greater than indicated in Fig 6 because low abundance and/or spotty distributions within towns result in low contributions to Bray-Curtis similarity within towns; that is not all species present were designated as typical species based on SIMPER analysis. Non-native snails and biotic homogeneity Non-native snail species were among the typical species in 11 of 12 towns (Fig 6). The Søren- sen dissimilarity of non-native snail assemblages increased with increasing distance among

towns (p = 0.047, R2 = 0.06; Fig 8D). Simpsons dissimilarity, a measure of species replacement, Fig 5. Relationships between abiotic factors (annual total rainfall and monthly mean low temperatures in January) and snail abundance and richness across the 12 surveyed towns. Snail abundance (green circles): A is rainfall; B shows low temperatures. Snail species richness (red circles): C is rainfall; D shows low temperatures. Multiple linear regression results are displayed on each graph. https://doi.org/10.1371/journal.pone.0234830.g005 PLOS ONE Diversity patterns of yard-dwelling snails across climate gradients PLOS ONE | https://doi.org/10.1371/journal.pone.0234830 August 28, 2020 9 / 18