Land‐use in Europe affects land snail assemblages directly and indirectly by modulating abiotic and biotic drivers

Abstract

Type and intensity of land‐use vary in space and time and strongly contribute to changes in richness and composition of species communities. In this study, we examined land snail communities in forests and grasslands in three regions of Germany. We aimed to quantify the extent to which snail density, diversity, and community composition in forests and grasslands are determined by (1) land‐use intensity, (2) abiotic drivers and (3) biotic substrates, and (4) whether these effects are consistent across regions. In total, we collected 15,607 snail individuals belonging to 71 species and analyzed both direct and indirect effects using structural equation modeling. Snail densities and their local diversity varied across regions and between forest and grassland habitats within a region albeit with contrasting trends. Community composition also differed among regions—more strongly in forests than in grasslands—and each habitat had unique species (18 in forests, 21 in grasslands). In general, the direct impact of land‐use on snail density, diversity, and community structure was on average nine (forests) and seven (grasslands) times lower than the impact of abiotic drivers and biotic substrates which both affected snail assemblages about equally. However, land‐use factors had indirect effects on snail responses through abiotic variables such as soil moisture and soil pH. Furthermore, land‐use factors also had indirect effects via changing biotic substrates, such as plant cover in grasslands and deadwood cover in forests. Our results show that land snails strongly respond to environmental gradients and add an important indicator taxon to the current evidence of land‐use impacts, highlighting the complexity of direct and indirect effects via biotic and abiotic drivers across regions in Central Europe.

Narrow environmental niches predict land-use responses and vulnerability of land snail assemblages

“…Our previous study [ 27 ] focused on land snail density, diversity and species composition and emphasized that direct impacts of land use on snail communities were on average lower than the impact of abiotic drivers and biotic substrates. However, unlike several studies on insects, few direct effects have been shown for wood harvesting in forests and mowing in grasslands on snail diversity [ 27 ]. How these direct land-use effects influence populations of single species and whether these effects are related to species-specific traits remains largely unclear.…”

“…Data for this study were already part of a previous analysis of biodiversity and community composition, i.e. Wehner et al [ 27 ] and are available at https://www.bexis.uni-jena.de/PublicData/PublicDataSet.aspx?DatasetId=24986 . Wehner et al [ 27 ] collected 15,607 snail individuals belonging to 71 taxa in three regions in Germany in the framework of the Biodiversity Exploratories Project ( http://www.biodiversity-exploratories.de ) [ 2 ].…”

“…Wehner et al [ 27 ] and are available at https://www.bexis.uni-jena.de/PublicData/PublicDataSet.aspx?DatasetId=24986 . Wehner et al [ 27 ] collected 15,607 snail individuals belonging to 71 taxa in three regions in Germany in the framework of the Biodiversity Exploratories Project ( http://www.biodiversity-exploratories.de ) [ 2 ]. The collaborative research unit addresses effects of land-use on biodiversity and biodiversity-related ecosystem processes in three regions: the Swabian Alb (ALB), a low-mountain range in South-West Germany (460–860 m a.s.l., 09° 10′ 49″–09° 35′ 54″ E/48° 20′ 28″–48° 32′ 02″ N), the Hainich-Dün (HAI), a hilly region in Central Germany (285–550 m a.s.l., 10° 10′24″–10° 46′ 45″ E/50° 56′ 14″–51° 22′ 43″ N) and the Schorfheide-chorin (SCH), a glacial formed landscape in North-East Germany (3–140 m a.s.l., 13° 23′ 27″–14° 08′ 53″ E/52° 47′ 25″–53° 13′ 26″ N).…”

“…In June 2017, Wehner et al [ 27 ] took five replicated surface samples from all 50 forest and 50 grassland experimental plots (EPs) in the Swabian Alb and the Hainich, and from 49 forest and 34 grassland plots in the Schorf-heide due to constrained accessibility (1415 samples in total). Shelled snails were subsequently determined to the species, genus or family level using [ 41 – 43 ].…”

“…Grassland plots (although not permanently flooded) in one region (Schorfheide) harbored large numbers of aquatic and semi-aquatic snails. In contrast to our previous analysis that covered all snails recorded [ 27 ], we excluded aquatic snails from the analyses since their role and responses to terrestrial environmental variables such as land-use in grasslands remain unclear,…”