1. We tested three hypotheses (productive energy, habitat heterogeneity, historical climate stability) to explain regional species richness patterns in subterranean habitats, which have less habitat/climatic variability than surface habitats.2. For the first time, we investigated the pattern of two species richness hotspots in the world's richest region in subterranean biodiversity in southeast Europe. We used distribution records for 388 species of beetles, the most species rich group of terrestrial subterranean fauna, belonging to subfamilies Trechinae (Carabidae) and Leptodirinae (Cholevidae), and mapped them onto a 20 9 20 km grid.3. We applied spatial and non-spatial multiple regression, using generalised linear models and spatial eigenvector mapping. The relative importance of each hypothesis, and of the spatial versus the environmental components, was assessed with variation partitioning. We analysed the total dataset as well as each subfamily separately. 4. Our results show that although the relative importance of species richness drivers differed among taxonomic groups, in most cases habitat heterogeneity had the biggest influence. It was followed by historical climate stability, while productive energy had a neglecting effect. This proves that even though habitat variability is smaller in subterranean than in surface habitats, its gradient is still strong enough to explain species richness patterns better than the other two hypotheses.5. Identification of the drivers shaping the two regional species richness hotspots within a global hotspot of highly endemic subterranean fauna is important for conservation practices. Additionally, we contribute to the general understanding of species richness patterns of insects, by providing the first detailed analyses on a regional scale for subterranean systems.

AimCommon species contribute more to species richness patterns (SRPs) than rare species in most studies. Our aim was to test this hypothesis using a novel model system, species living exclusively in subterranean habitats. They consist of mainly rare species (small ranges), only a few of them being common (large ranges), and challenge whether rare species are less important for the development of SRPs in this environment. We separately analyzed aquatic and terrestrial species.LocationWestern Balkans in southeastern Europe.MethodsWe assembled two datasets comprising 431 beetle and 145 amphipod species, representing the model groups of subterranean terrestrial and aquatic diversity, respectively. We assessed the importance of rare and common species using the stepwise reconstruction of SRPs and subsequent correlation analyses, corrected also for the cumulative information content of the subsets based on species prevalence. We applied generalized linear regression models to evaluate the importance of rare and common species in forming SRPs. Additionally, we analyzed the contribution of rare and common species in species‐rich cells.ResultsPatterns of subterranean aquatic and terrestrial species richness overlapped only weakly, with aquatic species having larger ranges than terrestrial ones. Our analyses supported higher importance of common species for forming overall SRPs in both beetles and amphipods. However, in stepwise analysis corrected for information content, results were ambiguous. Common species presented a higher proportion of species than rare species in species‐rich cells.Main ConclusionWe have shown that even in habitats with the domination of rare species, it is still common species that drive SRPs. This may be due to an even spatial distribution of rare species or spatial mismatch in hotspots of rare and common species. SRPs of aquatic and terrestrial subterranean organisms overlap very little, so the conservation approaches need to be habitat specific.

Seven new species of the cavernicolous and anophthalmous genus Thaumastocephalus Poggi, Nonveiller, Colla, Pavićević & T. Rađa, 2001 are described: T. bilandzijae sp. n., T. kirini sp. n., T. marsici sp. n., T. rujnicensis sp. n., T. slavkoi sp. n. and T. troglavi sp. n. from Croatia and T. dahnae sp. n. from Bosnia and Herzegovina. Aedeagi of all species are illustrated. A key to all species is provided. The records of all specimens of the genus treated here are given, and their distributions are discussed and shown on maps. The distribution of all genera of cavernicolous Pselaphinae in the Dinarides is discussed.