Local distribution patterns of harvestmen (Arachnida: Opiliones) in a Northern temperate Biosphere Reserve landscape: influence of orientation and soil richness

The study at a local scale of the fauna in a natural mountain landscape provides insights regarding the patterns and the factors influencing distribution. We test if each type of natural forest and some open habitats in the Muniellos Biosphere Reserve have their own unique harvestmen assemblages. We further investigate the presence of groups of sites sharing harvestmen assemblages and the factors and indicator species involved. Nineteen sites with well-known phytosociological association were sampled during nine surveys from late 2001 to 2002 by means of three sampling protocols. The quality of the inventories was assessed via the corresponding species accumulation curves. The cluster analysis using the Bray Curtis similarity index showed the presence of two main distinct groups of sites. One group consisted of seven lower forest sites, while the second group contained samples from more open sites and lighter forests. IndVal analyses show the first group has six characteristic species and the second group has one. ANOSIM analyses revealed that the harvestmen community composition was significantly different between the two clusters. Orientation appears to be one main driver of harvestmen assemblages on Mount Muniellos: a clear distinction between the two clusters appears along the boundary of shady to sunny habitats. The vegetal associations that house the higher harvestmen species richness have the higher soil richness. Seven rare and infrequent species were found in forests with richer soil.