The Pattern of Earthworm Diversity on the Western Slopes of Kopaonik Mountain in Serbia: An Empirical Test of Rapoport’s Altitudinal Rule ^†

The pattern of earthworm diversity along altitudinal gradients has rarely been investigated. The aim of the current study was to examine the patterns of earthworm diversity on the western slopes of Kopaonik Mountain. Earthworms were sampled in four-month periods (from April to July) in both 2018 and 2019. In total, 30 plots at altitudinal transects between 420 and 1950 m a.s.l. were sampled within two years’ fieldwork. Overall, 27 earthworm species belonging to 11 genera were found at the study sites. A combination of Pearson’s correlation, linear regression and cluster analysis (UPGMA) was used to determine the effects of altitude on earthworm diversity. Essentially, we found monotonically declining relationships between total abundance/species richness and altitudinal gradients (from 14 to 6 species and from 118 to 39 individuals). Cluster analysis revealed two patterns of earthworm community composition: one that characterizes a low altitude (up to 1000 m) and one that was observed at the middle and high altitudes (from 1000 m). Nevertheless, a high number of taxa with broad ecological tolerances was observed, which means an increase in the altitudinal range with increasing altitudes, thus supporting Rapoport’s altitudinal rule. Overall, this study provides new insights into the understanding of the effect of altitude on earthworm diversity.