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

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

The land snail faunas of limestone gorges of Romanian Carpathians were sampled to test the effect of geographic and environmental factors on the malacofauna richness and composition. A total of 134 sites within 28 limestone gorges were surveyed during 2011-2019 using a combined strategy of visual search and litter/topsoil analysis. Environmental variables such as geographic location, altitude, climate, microhabitat type, dominant vegetation, tree cover and width of the gorge were recorded to detect the relationship with species richness and composition. While the numbers of species, their identities and their abundance varied greatly among samples, both presence and absence data and quantitative multivariate analyses showed that region and climate or altitude (both strongly associated with region) accounted for far more variation than differences in tree cover and dominant microhabitat. Nevertheless, the effects of different habitat preferences were evident. The mixture of species with very restricted ranges within this Pleistocene refugium and those that have spread widely during the Holocene raise questions about the meaning of region when related to local richness and composition.

Moving past the challenges and misconceptions in urban adaptation research

Although the field of urban evolutionary ecology has recently expanded, much progress has been made in identifying adaptations that arise as a result of selective pressures within these unique environments. However, as studies within urban environments have rapidly increased, researchers have recognized that there are challenges and opportunities in characterizing urban adaptation. Some of these challenges are a consequence of increased direct and indirect human influence, which compounds long-recognized issues with research on adaptive evolution more generally. In this perspective, we discuss several common research challenges to urban adaptation related to (1) methodological approaches, (2) trait-environment relationships and the natural history of organisms, (3) agents and targets of selection, and (4) habitat heterogeneity. Ignoring these challenges may lead to misconceptions and further impede our ability to draw conclusions regarding evolutionary and ecological processes in urban environments. Our goal is to first shed light on the conceptual challenges of conducting urban adaptation research to help avoid the propagation of these misconceptions. We further summarize potential strategies to move forward productively to construct a more comprehensive picture of urban adaptation, and discuss how urban environments also offer unique opportunities and applications for adaptation research.

Biotic homogenization or riparian refugia? Urban and wild land snail assemblages along a subtropical precipitation gradient

A noted impact of urbanization is the tendency for biotic homogenization, or the increase of similarity of geographically disparate communities. On the other hand, some urban habitats harbor biodiversity native to their region, a role potentially important in xeric landscapes, with irrigation increasing the coverage and availability of mesic habitats in an otherwise water-limited landscape. We assessed the relative importance of urban yards as agents of biotic homogenization or riparian refugia by characterizing community composition of Tamaulipan thornforest land snail assemblages across a pronounced precipitation gradient in far south Texas, USA. We quantified α- and β-diversity and assessed whether the land snail fauna of urban yards are more similar to each other across a precipitation gradient than they are to their wild counterparts, as well as determined the significance of moisture in driving Tamaulipan thornforest β-diversity, both in terms of turnover (changing species composition) and nestedness (species loss). Sites with both the wild and wet conditions had the highest values of species richness and abundance. Urban land snail communities were significantly homogenized, outweighing the influence of the precipitation gradient. We did not find urban yards served as a refuge for native, moisture-dependent, riparian snails. Our analyses find that turnover, not nestedness, is the largest contributor to β-diversity in these assemblages. Studies of urbanization should address regional spatial scales to quantify how urbanization modifies regional biodiversity arising from background environmental gradients. Such an approach could lead to improved understanding of how large metroplex areas could be used to maintain and even promote biodiversity.