Changes in mean numbers of land snail species in relation to four environmental variables.

<p>Changes in mean numbers of land snail species in relation to four environmental variables.</p

Predicted species richness of grassland and forest vegetation in the Czech Republic (shapefiles)

ESRI shapefiles containing maps of species richness of grassland and forest vegetation in the Czech Republic modelled by Random Forest. Numbers of all, native, alien and Red List species were modelled for 16 sq. m plots for grasslands and 400 sq. m plots for forests. Model results were projected to a grid of 37,763 cells, each spanning 1.25' of longitude and 0.75' of latitude, which corresponds to approximately 1.5 × 1.39 km (2.09 sq. km)

Unimodal Latitudinal Pattern of Land-Snail Species Richness across Northern Eurasian Lowlands

<div><p>Large-scale patterns of species richness and their causes are still poorly understood for most terrestrial invertebrates, although invertebrates can add important insights into the mechanisms that generate regional and global biodiversity patterns. Here we explore the general plausibility of the climate-based “water-energy dynamics” hypothesis using the latitudinal pattern of land-snail species richness across extensive topographically homogeneous lowlands of northern Eurasia. We established a 1480-km long latitudinal transect across the Western Siberian Plain (Russia) from the Russia-Kazakhstan border (54.5°N) to the Arctic Ocean (67.5°N), crossing eight latitudinal vegetation zones: steppe, forest-steppe, subtaiga, southern, middle and northern taiga, forest-tundra, and tundra. We sampled snails in forests and open habitats each half-degree of latitude and used generalized linear models to relate snail species richness to climatic variables and soil calcium content measured in situ. Contrary to the classical prediction of latitudinal biodiversity decrease, we found a striking unimodal pattern of snail species richness peaking in the subtaiga and southern-taiga zones between 57 and 59°N. The main south-to-north interchange of the two principal diversity constraints, i.e. drought stress vs. cold stress, explained most of the variance in the latitudinal diversity pattern. Water balance, calculated as annual precipitation minus potential evapotranspiration, was a single variable that could explain 81.7% of the variance in species richness. Our data suggest that the “water-energy dynamics” hypothesis can apply not only at the global scale but also at subcontinental scales of higher latitudes, as water availability was found to be the primary limiting factor also in this extratropical region with summer-warm and dry climate. A narrow zone with a sharp south-to-north switch in the two main diversity constraints seems to constitute the dominant and general pattern of terrestrial diversity across a large part of northern Eurasia, resulting in a subcontinental diversity hotspot of various taxa in this zone.</p></div

Mean numbers of land snail species recorded in 100 m² plots at 29 sites located along a latitudinal transect in the West Siberian Plain between 54.5° and 67.5°N.

<p><b>A</b>, species from forest and open habitats counted separately; <b>B</b>, means from all plots at each site shown with patterns of four environmental variables visualized using the locally-weighted polynomial regression.</p

Study area with the position of 29 sampling sites along the transect.

<p>Study area with the position of 29 sampling sites along the transect.</p

data

File with data on individual species. Each line corresponds to one species, with value of disturbance frequency indicator value, disturbance severity indicator value, and Ellenberg indicator value for nutrient

Appendix C. Cumulative numbers of alien and native species in analogous habitats.

Cumulative numbers of alien and native species in analogous habitats

Appendix A. Crosswalk between vegetation classification units.

Crosswalk between vegetation classification units

Diversity and Biotic Homogenization of Urban Land-Snail Faunas in Relation to Habitat Types and Macroclimate in 32 Central European Cities

<div><p>The effects of non-native species invasions on community diversity and biotic homogenization have been described for various taxa in urban environments, but not for land snails. Here we relate the diversity of native and non-native land-snail urban faunas to urban habitat types and macroclimate, and analyse homogenization effects of non-native species across cities and within the main urban habitat types. Land-snail species were recorded in seven 1-ha plots in 32 cities of ten countries of Central Europe and Benelux (224 plots in total). Each plot represented one urban habitat type characterized by different management and a specific disturbance regime. For each plot, we obtained January, July and mean annual temperature and annual precipitation. Snail species were classified into either native or non-native. The effects of habitat type and macroclimate on the number of native and non-native species were analysed using generalized estimating equations; the homogenization effect of non-native species based on the Jaccard similarity index and homogenization index. We recorded 67 native and 20 non-native species. Besides being more numerous, native species also had much higher beta diversity than non-natives. There were significant differences between the studied habitat types in the numbers of native and non-native species, both of which decreased from less to heavily urbanized habitats. Macroclimate was more important for the number of non-native than native species; however in both cases the effect of climate on diversity was overridden by the effect of urban habitat type. This is the first study on urban land snails documenting that non-native land-snail species significantly contribute to homogenization among whole cities, but both the homogenization and diversification effects occur when individual habitat types are compared among cities. This indicates that the spread of non-native snail species may cause biotic homogenization, but it depends on scale and habitat type.</p> </div

Sample-based rarefaction curves showing an increase in the cumulative number of native and alien land-snail species recorded in 32 Central European cities with increasing number of cities sampled.

<p>Dashed lines indicate 95% confidence intervals.</p