Spider diversity and ecological drivers in hill range environments of Pampa biome

Environmental complexity can drive spider diversity and guild distribution across the landscape. Grasslands and other natural areas in the South American Pampa biome have been affected in the last century mainly by extractive activities (eg forestry) or changes in land use (eg agricultural and livestock production). In this scenario of human disturbances, efforts are required to describe the biodiversity of these threatened environments. The aim of this study is to describe and compare the spider communities of a hill range landscape of the Pampean region in Uruguay, which includes hillside forests, riparian forests and natural grasslands, and to evaluate the influence of environmental complexity in these communities. Sampling was carried out in autumn and spring using pitfall traps, G-Vac and manual collection. Environmental variables of soil surface temperature and moisture, leaf litter depth, ground vegetation cover, tree canopy cover and herbaceous plant species richness were recorded. Spider species richness and diversity were highest in grasslands. Hillside forests, riparian forests and grasslands were different in terms of their spider species composition. A high variability of species composition was found within hillside forests and grasslands. The environmental variables that explained differences in abundance among spider guilds in hillside forests were the canopy cover (mainly for ground hunters, sheet web weavers and spatial web weavers) and soil moisture. In riparian forests the main environmental variable driving spider abundance was the leaf litter depth (especially for orb web weavers, space web weavers, stalkers and ambushers) while in grasslands it was the soil moisture (mainly for ambushers, space web weavers and sheet web weavers). Spider indicator species were found for the studied environments. Our results provide knowledge about the spider diversity in hill range environments of the Pampa biome, highlighting the need for urgent implementation of conservation plans in these natural environments.