Epigean Spider Diversity in the Classical Karst

The classical Karst (Kras in Slovenian) is a limestone karst plateau of south-western Slovenia and north-eastern Italy surrounded by flysch or alluvial areas. We explored surface spider species richness in the Karst by conducting a season-long quantitative inventory of the epigean fauna. By examining three localities, each with three succession-stage sites (grassland, overgrowth, forest) we tested for differences in alpha and beta diversity among different successions based on species incidence data. A total of 90 ethylene glycol pitfall traps (10 traps per each of nine sites) operated between 24. V. 2005 and 20. VII. 2006. We recorded a total of 3681 adult spiders belonging to 136 species, 82 genera and 30 families. Of these 28 species are new records for Slovenia. The observed species richness and total adult spider abundances were highest in the spring and early summer, and among succession stages they were highest in grassland (95 species; 1563 individuals), followed by overgrowth (81 species; 1047 individuals) and forest (64 species; 1071 individuals). By comparing our results with previous pitfall samplings in the Dinaric karst, we conclude that the sampling effort needed for a meaningful estimation of epigean spider diversity was barely sufficient in our study when all data were combined, but completely inadequate in previous samplings. In our study the total species richness was estimated by nonparametric statistics to lie at 181, thus 25 % richer than observed. The spider fauna of Slovenia, including this contribution, currently standing at 615 species, continues to be inadequately known.