Understanding hotspots within a global hotspot – identifying the drivers of regional species richness patterns in terrestrial subterranean habitats

Abstract

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.

Modelling the future spread of native and alien congeneric species in subterranean habitats — the case of Meta cave-dwelling spiders in Great Britain

“…Topographic heterogeneity -here approximated using elevation data (see Zagmajster et al, 2014;Eme et al, 2015Eme et al, , 2017Bregović & Zagmajster, 2016) -rather than the presence of carbonate substrates, emerged as the second most important factor in constructing the distribution models (Table 1). A strong correlation with limestone areas would indeed only be expected in calciphilous invertebrate species (e.g., certain species of Gastropoda), or those largely restricted to natural caves.…”

“…In addition, rain water represent an important route for organic materials to enter hypogean ecosystems. Therefore, Bio12 may represent a proxy for external energy inputs (see also Bregović & Zagmajster, 2016).…”

“…Elevation range is considered to be one of the simplest surrogate of topographic heterogeneity (Zagmajster et al, 2014;Eme et al, 2015Eme et al, , 2017Bregović and Zagmajster, 2016), thus representing a proxy for habitat availability. This variable also influence the general thermal conditions (Badino, 2010 It represent a proxy of the general availability of subterranean habitats in carbonate substrates (Christman & Culver, 2001, Christman et al, 2016).…”

Climate change and its impact on epigean and hypogean carabid beetles

“…comm.). Those "new appearances" happen most independently from the hotspot areas and the sampling intensity evaluations proposed in different manners (and very convincingly) by more authors especially for the northwestern Balkans (57,58). Many "aphenopsian" Orotrechus species have found in an exhaustively explored area of the southeastern Alps, and Lovriciina taxa have discovered both in intensively and non-intensively explored geographic sectors.…”

“…The study of subterranean life is the target of Biospeology, a science born in Slovenia in the first half of the 19th century (47), and today cave beetles are known from all continents and especially from karstic areas, even if the Dinaric Karst of the Western Balkans remains a global biodiversity hotspot for obligate subterranean beetles (48). Subterranean beetles live especially in non-glaciated areas that showed in the last geo-periods a long-term stability of environmental conditions (49), especially of amounts of precipitation (57).…”