Species diversity, abundance and body size in rocky-shore Mollusca

onto the S-I plane a power-law emerges where SI 0.5 . Such richness-abundance relationships were shown to hold across numerous body types and a 100,000-fold range of body sizes in five different orders of insects. This finding points to an associa- tion between interspecific resource division, abundance and diversity in natural communities that is independent of body size. Moreover, their data suggests that within any taxonomic group, undescribed species are more likely to be of intermedi- ate sizes. This has important implications regarding current estimates of global diversity 4 , and the causes for this diversity, provided that empirical evidence from other taxonomic groups should turn up similar relationships. To investigate if these results represent a general rule, we explored these rela- tionships using mollusc datasets from rocky shore macrofaunal communities sampled along a biogeographical range along the southern Iberian Peninsula. We sampled littoral faunas along continuous belt transects perpendicular to the water's edge 5,6 at 20 sites stretching from Vila Nova de Milfontes on the Atlantic coast of Portugal to La Manga del Mar Menor, on the Spanish Mediterranean coast (Fig. 2). All samples were taken from outward-facing, unob- structed rocky coasts, with a slope of between 30°-60° to the horizontal during the months of July-September 1993 at low water. At each site a prior generalised shore search was under- taken in order to select the most appropriate and representa- tive location for the transect 7-10 .