Spatial Niches of Opiliones (Arachnida) from Vitosha Mountains, Bulgaria

Abstract

The spatial niche breadths of 23 opilionid species (Paranemastoma radewi, P. aurigerum ryla, Pyza bosnica, Carinostoma ornatum, Mitostoma chrysomelas, Trogulus tricarinatus, T. closanicus, Phalangium opilio, Opilio parietinus, O. saxatilis, O. dinaricus, O. ruzickai, Rilaena balcanica, R. cf. serbica, Lophopilio palpinalis, Zachaeus crista, Z. anatolicus, Lacinius horridus, L. ephippiatus, L. dentiger, Odiellus lendli, Mitopus morio, Leiobunum rumelicum) were estimated using Hill’s index (N2). Harvestmen were sampled from 54 habitats (grouped in 21 habitat types) in Vitosha Mountains, Bulgaria. A significant correlation between the number of occupied habitats and niche breadth was established (R2=0.3055, p=0.003676). The harvestmen species were classified in two groups: (1) species with ‘‘narrower’’ niches (1⩽ N2⩽ 6) and (2) species with ‘‘wider’’ ecological niches (N2≥6). The first group contains harvestmen that are relatively more dependent on the biotic and abiotic environmental factors. The second group includes species occurring mostly in forest habitats or both in forest and open grass habitats. A comparative analysis of niche dimensions revealed specific guilds of harvestmen species. The closely related species have strongly different niche dimensions, which might be an important feature for avoiding or reducing the interspecific competition. Various ranked-abundance distribution models were fitted to the dataset. The relevant species-abundance model for the harvestmen assemblages studied is the Preston’s Log-normal Model