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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. [ABSTRACT FROM AUTHOR]

Trait-based approaches have increased significantly in community ecology during the last decade. This is not least because studies on biodiversity–ecosystem functioning relationships became a major topic in ecology. Species’ functions in ecosystems are mediated by their traits. For a better understanding of the relationships between environmental drivers, the community composition of organisms and ecosystems functioning, it is crucial to understand how these relationships are mediated by the communities’ trait composition. While there are world-wide efforts to set up trait databases, most have so far focused on plants and species-poorer taxa such as birds or amphibians. In contrast, for insects, the large number of species makes the gathering of comparable trait data a challenging task. In addition, there is the danger that generic trait information, which is available from common textbooks, may not be sufficient to detect the response of insect communities to environmental change or the consequences of trait changes for ecosystem functioning. One method to overcome this is to take morphometric measurements of species. In this study we measured morphometric traits of a total of 179 Heteroptera species that were sampled by sweep-netting on a total of 150 managed grassland plots across three regions in Germany between 2008 and 2012. These plots represent the whole range of grassland management intensities from extensively used pastures to mown pastures to intensively managed and fertilized meadows. In this paper we provide a database of mean values of 23 morphometric measures across sex and morphotypes for each sampled Heteroptera species. Morphological traits are assumed to be related to their adaptation and function in the environment. Thus the relative morphometric traits can be used as proxies for ecological features of a species that may affect its performance or fitness. Our database can be used by future trait-based studies for developing and testing hypotheses of the functional significance of these traits. Examples include studying the functional responses of insect communities to environmental drivers or studying how the change in trait composition affects ecosystem processes. [ABSTRACT FROM AUTHOR]