Species richness patterns of obligate subterranean beetles (Insecta: Coleoptera) in a global biodiversity hotspot – effect of scale and sampling intensity

Abstract

We studied species richness patterns of obligate subterranean (troglobiotic) beetles in the Dinaric karst of the western Balkans, using five grid sizes with cells of 80 × 80, 40 × 40, 20 × 20, 10 × 10, and 5 × 5 km. The same two hotspots could be recognized at all scales, although details differed. Differences in sampling intensity were not sufficient to explain these patterns. Correlations between number of species and number of sampled localities increased with increasing cell size. Additional species are expected to be found in the region, as indicated by jackknife 1, jackknife 2, Chao2, bootstrap, and incidence‐based coverage (ICE) species richness estimators. All estimates increased with increasing cell size, except Chao2, with the lowest prediction at the intermediate 20 × 20 km cell size. Jackknife 2 and ICE gave highest estimates and jackknife 1 and bootstrap the lowest. Jackknife 1 and bootstrap estimates changed least with cell size, while the number of single cell species increased. In the highly endemic subterranean fauna with many rare species, bootstrap may be most appropriate to consider. Positive autocorrelation of species numbers was highest at 20 × 20 km scale, so we used this cell size for further analyses. At this scale we added 137 localities with less positional accuracy to 1572 previously considered, and increased 254 troglobiotic species considered to 276. Previously discovered hotspots and their positions did not change, except for a new species‐rich cell which appeared in the south‐eastern region. There are two centres of troglobiotic species richness in the Dinaric karst. The one in the north‐west exhibited high species richness of Trechinae (Carabidae), while in the south‐east, the Leptodirinae (Cholevidae) were much more diverse. These centres of species richness should serve as the starting point for establishing a conservation network of important subterranean areas in Dinaric karst.

VIEWPOINT. Is the Australian subterranean fauna uniquely diverse?

“…Even within this geomorphological constraint (i.e. it is patchily distributed, Fong and Culver 1994;) the density of caves and the sampling intensity by generations of researchers in these regions have provided biologists with the opportunity to efficiently document caves and their fauna (Christman and Culver 2001;Zagmajster et al 2008). Consequently, knowledge of these regions and their biodiversity, phylogeography and functional ecology are well progressed (Gibert et al 1994;Wilkens et al 2000;Culver and White 2004).…”

The world's deepest subterranean community - Krubera-Voronja Cave (Western Caucasus)

“…Since the description of the cave salamander Proteus anguinus by Laurenti in 1752, thousands of cave-dwelling animals (troglo-and stygobionts) have been recorded all over the world, except in Antarctica (Culver et al, 2006;Gibert & Culver, 2009). Many speculations about biodiversity patterns and species distributions, and the relationship between cave length and species numbers have been made by scientists in the last years (Culver et al, 2006;Schneider & Culver, 2004;Zagmajster et al, 2008), but the vertical limit of its distribution in function of cave's great depths remain unknown.…”

Climate change and its impact on epigean and hypogean carabid beetles

“…Along the tread that conducts from alluvial plains to rocky substrates and higher elevations, a possible "blind end" is represented by the subterranean evolution (47), that leads first to brownish microphthalmous forms and finally to cave dwelling anophthalmous more or less pale-yellow beetles, that acquired the so called "troglomorphic" habitus. 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).…”