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

temperatures [50, 51] can affect land snail composition, and indeed both climate variables explained much of the variation in taxonomic composition among towns, together explaining one-half (50.11%) of this variation. Native snails should be adapted to local seasonal and year-to-year fluctuations in tempera- ture, whereas some non-native snails may be strongly affected by ambient climatic conditions because non-natives may originate from regions with a different climate and, as a conse- quence, be poorly adapted to local conditions—although many non-native snails are tolerant generalists. An incongruence between climatic tolerance and species’ presence may occur in species that are dispersed primarily by humans, as unintentional human-assisted dispersal can be both rapid and long distance. Indeed, climate has become a driver in worldwide land snail distribution patterns as a result of increased human-mediated dispersal [52]. Cold temperatures decrease the daily and seasonal activity periods of snails and very cold temperatures can be lethal. Although thermal limits are poorly known for most snail species, the thermal tolerance of one non-native from this study, namely Cornu aspersum, has been studied in detail [e.g., 53]. Cornu has limited tolerance to freezing temperatures, and indeed, we found Cornu in only the southern tier of sites, specifically in Altus, where the mean low temperature in January is -2.5˚C. Populations of Cornu also live in Norman [23], which has a similar low mean temperature, and in several urban areas in New Mexico [54], where winter

low temperatures are colder. Although physiologically ill-adapted to these lower temperatures, the species and other freeze-susceptible snails likely persist through behavioral adaptation, Fig 9. Relationships between the homogenization index and distance between pairs of towns (N = 66). The dashed blue horizontal line is the transition between biotic homogenization (> 0) and biotic differentiation (< 0). https://doi.org/10.1371/journal.pone.0234830.g009 PLOS ONE Diversity patterns of yard-dwelling snails across climate gradients PLOS ONE | https://doi.org/10.1371/journal.pone.0234830 August 28, 2020 13 / 18