The species-area relationship of terrestrial isopods (Isopoda

Abstract

Data on species richness of terrestrial isopods (Oniscidea) from central Aegean islands (Greece), together with previously published data sets from other taxa and areas, are critically analysed under the basic premises of ecological biogeography. Habitat diversity seems to be the most important determinant of species richness for Oniscidea, although the relation to area is also significant. Comparison with other data sets demonstrates that the best fit model of the species-area relationship is case-specific and usually not unique, since the assumptions for appropriate use of any particular model (logS/logA, S/A or S/logA) cannot be satisfied by all species richness data sets, and since confidence limits around regression coefficients are usually broad for the relatively limited sizes of island groups. The values of slopes and intercepts of the species-area regression lines seem to be statistical artefacts that encompass the effects of several intervening factors, such as the data set size and range, and should be checked accordingly before any biological statements about differences between taxa or island groups can be made.