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

Abstract

Residential yards constitute a substantive biodiverse greenspace within urban areas. This biodiversity results from a combination of native and non-native species and can contribute to biotic homogenization. Geographical climatic patterns affect the distribution of native species and may differently affect non-native species. In this study, we examined biodiversity and biotic homogenization patterns of yard-dwelling land snails across 12 towns in Oklahoma and Kansas (USA). The 3 x 4 array of towns incorporated a N-S winter temperature gradient (mean low January temperature range =-8.4 to 0.1˚C) and an E-W annual rainfall gradient (annual rainfall range = 113.8 to 61.3 cm/yr). Ten yards per town were surveyed. We hypothesized that mild winter temperatures and greater annual rainfall would be associated with greater snail abundance and richness, and that the presence of non-native species would contribute to biotic homogenization. Non-native snails were present and often abundant in all towns. Snail communities varied with both rainfall and cold temperature. Contrary to our prediction, snail abundance was inversely related to annual rainfall-likely because drier conditions resulted in greater yard watering that both augmented rainfall and maintained moist conditions. Sørensen similarity between towns for the entire land snail community and for only non-native species both showed distance-decay patterns, with snail composition becoming less similar with increasing distance-patterns resulting from species turnover. The biotic homogenization index also showed a distance-related pattern, such that closer towns were more likely to have biotic homogenization whereas more distant towns tended to have biotic differentiation. These results support the concept that biotic homogenization is more likely regionally and that climatic changes over distance result in species turnover and can reduce spatially broad biotic homogenization.

Land Snails at the Zoo: A Biodiverse Community with Conservation and Educational Potential

“…There is very little information on non-captive land snails associated with zoos in the United States; indeed, the only reference we found was a statement that Ventridens demissus was a common snail in the Atlanta Zoo, where it was also the only species found on the Zoo's green roofs [26]. This species was found at all sites in our survey and is common in both regional plant nurseries [22] and yards [25,35]. An interesting observation associated with this species is the rasping of empty shells, presumably as a source of calcium.…”

“…Nearly all OKC Zoo sites had both native and non-native species, with only a single site having two non-native species and no native species. This mix of native and non-native species is typical of regional urban yards [25,30,35], whereas parks and natural areas with fewer plantings may have relatively fewer non-native species of snails [27].…”

Messages in the mucus: Selection of land snail resting sites based on the presence of mucus from conspecifics and other species

“…However, we found that the presence of mucus from snails of different species had no statistical effect on resting site selection, except for the apparent avoidance of mucus from individuals of Patera appressa . During previous fieldwork by E. A. Bergey (e.g., Bergey, 2019; Bergey & Whipkey, 2020), resting individuals of C. aspersum were not observed in association with any other snail taxa, either where resting on vertical surfaces (e.g., on house foundations) or in sheltering locations (e.g., under logs). In contrast to our results, avoidance, as indicated by a lack of trail following, was found among five species of Hawaiian tree snails that did not follow trails of other species but followed trails of conspecifics (Holland et al, 2018).…”

Geographical and environmental patterns of Carpathian land snail faunas in a region of high endemicity

“…Other studies are showing comparable results for terrestrial habitats. Thus, precipitation seasonality was singled as the best predictor of soil invertebrate richness in agricultural ecosystems in China 49 , while, in urban habitats, snail abundance was negatively associated with increasing rainfall and positively but weakly associated with higher temperatures during the winter 50 . The effect of precipitation seasonality on species richness, in our case, could be just another way to capture the effect of Submediterranean climate, characterized by a lower seasonality of precipitation.…”