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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 (γ-diversity); 2—island (α- and β-diversity between the islands); 3—sites (α- and β-diversity within each island). Quantitative and semi-quantitative soil sample replicates were collected during the wet season (autumn, 1999) in Lampedusa and Linosa, the two major islands of the archipelago. Data revealed that the sample α-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 (β-diversity) was very high at every spatial scale, from the sites to the archipelago. Biogeographical results highlighted great differences between faunas in the two islands. The formulation of hypotheses for biodiversity 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. [Copyright &y& Elsevier]

We investigated the morpho-functional relationships underlying shell use and the role of shells as a resource in Pagurus prideaux and Paguristes eremita, collected along a bathymetric cline in the Sicilian Channel (southern Italy). These relationships were influenced by the presence of epibiont anemones, which colonize gastropod shells inhabited by hermit crabs. Sea-anemones appeared to play a different role in the shell use of the two species of crabs. In P.prideaux, relationships with Adamsia palliata determined the use of globose shells (mainly Naticidae with a height/width ratio <1) and of small and damaged shells; in this case, the shell primarily played the role of a substrate for the settlement of anemones, and consequently its inhabiting and protective function tended to become less important. In P.eremita, relationships with the anemone Calliactis sp. and tube dwelling epibionts are correlated with the use of large, heavy shells with respect to the size of the crabs and also of well conserved shells; these shells offer an extensive surface for anemone settlement. In this case, the shell played a double role: an inhabiting-protective resource for the crab as well as a substrate for the anemone. Further experimental work will aim at testing these hypotheses, in an attempt at validating the proposed models and explaining the observed patterns. [ABSTRACT FROM AUTHOR]