The effects of spatial scale on the assessment of soil fauna diversity: data from the oribatid mite community of the Pelagian Islands (Sicilian Channel, southern Mediterranean) Tancredi Caruso a, *, Ruggero Noto La Diega b , Fabio Bernini b a Department of Environmental Sciences “G. Sarfatti”, University of Siena, via Mattioli 4, 53100 Siena, Italy b Department of Evolutionary Biology, University of Siena, via A. Moro 2, 53100 Siena, Italy Received 29 June 2004; accepted 28 January 2005 Available online 14 March 2005 Abstract The effects of spatial scale on the assessment of soil biodiversity were investigated through a field study conducted in the Pelagian Islands, Sicilian Channel, southern Mediterranean. The oribatid mite community in this archipelago was investigated from both an ecological and a biogeographical point of view. The following hierarchically nested spatial scales were considered: 1—archipelago (c-diversity); 2—island (a- and b-diversity between the islands); 3—sites (a- and b-diversity within each island). Quantitative and semi-quantitative soil sample repli- cates were collected during the wet season (autumn, 1999) in Lampedusa and Linosa, the two major islands of the archipelago. Data revealed that the sample a-diversity of the two islands is similar. The density of species followed a geometrical trend (a few dominant species with the remainder fairly uncommon) typical of communities in which a single environmental factor dominates species ecology. Community structure differed significantly between the two islands. Species turnover (b-diversity) was very high at every spatial scale, from the sites to the archi- pelago. Biogeographical results highlighted great differences between faunas in the two islands. The formulation of hypotheses for biodiver- sity patterns is strongly scale dependent: the heuristic and conservation value of the biogeographical approach increases from local to regional scales, because the importance of historical factors increases while that of ecological factors decreases. © 2005 Elsevier SAS. All rights reserved. Keywords: Soil biodiversity; Scale; Oribatid mites; Distribution; Community structure; Biogeography 1. Introduction In recent years, soil biodiversity has become one of the most important issues in nature conservation and manage- ment of land systems (Bengtsson et al., 2000; Wolters, 2001; De Goede and Brussaard, 2002). Several studies have been undertaken at different spatial and temporal scales on struc- tural and functional aspects of soil animal diversity (Bengts- son et al., 2000; Wolters, 2001; Ettema and Wardle, 2002; Migliorini et al., 2002). Research has highlighted many inter- esting macroecological issues. One of the most important is the relationship between a- and c-diversity (Wolters, 2001). The definition of these two kinds of diversity is scale- dependent, with a-diversity hierarchically nested in c-diversity (Whittaker, 1960; Whittaker, 1972; Magurran, 1988). Alpha- diversity is usually defined at a local scale and c-diversity at a regional scale (Whittaker, 1960; Whittaker, 1972; Magur- ran, 1988). Species turnover is defined by b-diversity (Whit- taker, 1960; Whittaker, 1972; Magurran, 1988). Due to hier- archical relationships between a-, b- and c-diversity indices, biodiversity studies require a multiscale approach (Wolters, 2001; Ettema and Wardle, 2002; Githaiga-Mwicigi et al., 2002; Nekola, 2003). The present paper investigates the effects of spatial scale on the assessment of soil fauna diversity through a field study conducted on oribatid mites in the Pelagian Islands (Sicilian Channel, southern Mediterranean). Islands have always been of central interest to biodiversity and biogeographical research (MacArthur and Wilson, 1967). The limited study area and relatively simple structure of insular ecosystems allow deep probing of ecological and biogeographical issues and testing * Corresponding author. Tel.: + 39 0577232877, fax: + 39 0577232806. E-mail address: tancredicaruso@unisi.it (T. Caruso). Acta Oecologica 28 (2005) 23–31 www.elsevier.com/locate/actoec 1146-609X/$ - see front matter © 2005 Elsevier SAS. All rights reserved. doi:10.1016/j.actao.2005.01.006