Environmental correlates of community structure in springtails (Collembola) from Romanian caves

Geographical isolation, habitat quality and habitat size are known as driving factors shaping species communities and richness. We analysed cave-dwelling springtail communities from 187 caves of the Carpathian Mountains and the Dobrogea Region across Romania. These caves differ in size, geographical isolation, habitat heterogeneity and age, and in the surrounding environmental conditions. Based on these data we tested for potential effects of environmental factors on species composition and richness. Despite high species turnover we found that caves which are geographically close to each other, at similar altitudes and with similar climatic conditions tend to have a more similar species composition than expected from random colonization. Particularly important for current species spatial distributions were past (glacial) environmental conditions. We found that co-occurring species are taxonomically more clustered than expected by chance. In turn, species traits, namely dispersal ability and body size and shape, were only of minor influence and did not significantly affect community assembly. These findings are consistent with long-term isolation and cave specific speciation/extinction dynamics. Our study adds to the increasing evidence that isolated habitat islands might maintain a stable although species-poor fauna due to a trade-off between past colonization, speciation and extinction.