Status assessment survey for springtails (Collembola) in Illinois caves: the Salem Plateau

The primary goal of this study was to survey the springtail (Hexapoda: Collembola) fauna of caves in the Salem Plateau of southwestern Illinois using structured sampling protocols to provide semi-quantitative abundance data and to assess the completeness of our knowledge of Illinois cave springtails. In 2009, eight caves (Wizard Cave, Pautler Cave, Spider Cave, Wanda’s Waterfall Cave, Illinois Caverns, Stemler Cave, Hidden Hand Cave and Bat Sump Cave) in Monroe and Saint Clair counties, Illinois, were sampled using a combination of methods, including pitfall traps, Berlese funnel processing of leaf and other plant litter, and hand collections by quadrat, on drip pools, free standing bait and random searches. Use of these varied sampling methods allowed us to evaluate the most effective survey methods for this group of arthropods. In total 49 species of springtails were found, of which 7 are new to science, 8 others represent new records for Illinois and 18 are new cave records for the species. This more than doubles the number of springtails species known from caves in the Salem Plateau region. More than half (29) of the species reported are ranked as rare at the state level (i.e., S1-S2). The ranking of a few species as rare in Illinois is probably an artifact of the relatively poor knowledge of the fauna of the state. Some other species ranked rare are probably actually rare in the state, as they represent populations at the limit of the distributional range of the species, yet others, such as the Pygmarrhopalites species, are probably truly rare and endemic to the region. The combination of pitfall trapping, random hand collections and Berlese funnel extractions accounted for more than 85% of the specimens counted and nearly 45% of the species collected. Examination of drip pools produced only 2% of the counted specimens, but 30% of the species reported. Three species accounted for 71% of all individuals collected and almost half (49.0%) the species were represented by only one or two specimens. Analysis of species accumulation curves using several estimators of species richness indicated that the rate of species accrual is far from asymptotic, suggesting our sampling is incomplete. The final estimates of the true number of springtail species ranged from 60.2 to 105.4, suggesting that an additional 11 to 56 springtail species may yet be detected in the region. Based on these results we conclude that pitfall traps, Berlese funnels and examination of drip pools and hand collections in other cave habitats are the four most effective ways to sample for cave springtails. We also conclude that the total number of species in Salem Plateau caves could be more than twice what we recorded in the present study, and that many more new species and state records will be found once caves in other Illinois karst regions are more thoroughly examined.