Tracking the ice: Subterranean harvestmen distribution matches ancient glacier margins

Environmental factors shaping copepod distributions in cave waters of the Lessinian unsaturated karst (NE-Italy)

The unsaturated karst represents a transitional zone connecting the land surface to the water table of the underlying saturated zone through percolating water and small perched aquifers. It constitutes a significant groundwater reservoir and hosts a high biodiversity of specialized and endemic species. Whereas investigating this ecotone can shed light on the invertebrate diversity of the whole karst system, ecological studies in the unsaturated karst have been hampered by access, mapping, and sampling challenges. We studied the unsaturated zone of 52 caves in the Lessinian Massif (NE-Italy), which is dominated by carbonate rocks interspersed with spot areas composed mainly of igneous rocks. Our aim was to understand which ecological and historical factors may have shaped the distribution of the groundwater crustacean copepods at a regional spatial scale in the Lessinian unsaturated karst. We collected 33 species belonging to the orders Harpacticoida and Cyclopoida. Species richness estimators and related species accumulation curves suggest an exhaustive sampling effort. A hydrologic analysis performed in a Geographic Information System environment divided the study area in three distinct drainage basins: Eastern Lessini, Lessinian Core, and Western Lessini. Regression analyses indicated that richness of non-stygobitic copepods (i.e., surface-water species which exploit groundwater for different purposes) was mainly driven by inter-basin differences. Richness of stygobitic copepods (i.e., obligate groundwater dwellers) was instead strongly related to lithological features and responded negatively to surface thermal variability. Next, we used a kernel density estimation to spatially explore diversity patterns in the area. The highest density of stygobitic harpacticoids was identified in the Eastern Lessinian basin, which is lithologically more heterogeneous and surrounded by practically non-aquiferous igneous rocks that may limit dispersal. Conversely, the Western Lessinian basin hosted a high density of stygobitic cyclopoid species. This spatial pattern suggests different colonization pathways for the two taxa, with a strong effect of igneous rocks in hampering dispersal of most harpacticoids. Lithological barriers seemingly did not affect non-stygobitic copepods, which were found across the whole area. Altogether, these results emphasize the key role played by the interaction of hydrological features, climate, and lithology in determining different copepod biodiversity patterns in the unsaturated karst.

Seasonal abundance and spatio-temporal distribution of the troglophylic harvestman Ischyropsalis ravasinii (Arachnida, Opiliones, Ischyropsalididae) in the Buso del Valon ice cave, Eastern Italian Prealps

We explore the population of the troglophilic harvestman Ischyropsalis ravasinii inhabiting the Buso del Valon ice cave located in the Italian Prealps. Spatial and temporal distributions of the specimens are investigated in relation to the variation of environmental abiotic conditions in the cave, such as the seasonal temperature and substrate surface typology. Our results show that I. ravasinii is distributed unevenly in the cave, most of individuals being present in the scree-covered section of the cave with superficial activities limited to the warm seasons only. In addition, our data suggests that the presence of a thick layer of rocky debris, together with high humidity and cold temperatures, are important limiting factors for the species. Seven additional species of harvestman are recorded in the cave, including the congeneric troglophilic species Ischyropsalis strandi. This is the first known record of these two troglophilic Ischyropsalis species coexisting within the same cave. An updated map of the distribution of I. ravasinii and I. strandi in the Italian Prealps is provided.

Local- versus broad-scale environmental drivers of continental β-diversity patterns in subterranean spider communities across Europe

Macroecologists seek to identify drivers of community turnover (β-diversity) through broad spatial scales. However, the influence of local habitat features in driving broad-scale β-diversity patterns remains largely untested, owing to the objective challenges of associating local-scale variables to continental-framed datasets. We examined the relative contribution of local- versus broad-scale drivers of continental β-diversity patterns, using a uniquely suited dataset of cave-dwelling spider communities across Europe (35-70° latitude). Generalized dissimilarity modelling showed that geographical distance, mean annual temperature and size of the karst area in which caves occurred drove most of β-diversity, with differential contributions of each factor according to the level of subterranean specialization. Highly specialized communities were mostly influenced by geographical distance, while less specialized communities were mostly driven by mean annual temperature. Conversely, local-scale habitat features turned out to be meaningless predictors of community change, which emphasizes the idea of caves as the human accessible fraction of the extended network of fissures that more properly represents the elective habitat of the subterranean fauna. To the extent that the effect of local features turned to be inconspicuous, caves emerge as experimental model systems in which to study broad biological patterns without the confounding effect of local habitat features.