Species and habitat biodiversity measure and conservation at different scale in small Mediterranean islands

Small islands are geographically and ecologically well-defined areas in whichbiological processes are easier to schematize than in the mainland. There is a vastrange of biodiversity measures, due to the large concept of biodiversity and therange of spatial, temporal and taxonomic scales used. Many existing measuresare well designed and informative. But, very often they are inadequate for purposesbeyond those for which they were specifically designed. Knowledge ontrends in biodiversity loss is hindered by the absence of reliable basic data formost groups of organisms as well as habitats. Plants are primary producers andkey structural elements for most ecosystems and islands are among the best floristicallyknown territories in the Mediterranean.Large-scale habitat measurements have been aided greatly by advances in remotesensing and GIS software. However, the degree of resolution of this techniqueis still not adequate for many purposes, such as monitoring many habitatsthat occurs on the islands (e.g. temporary Mediterranean pools or ephemeraltherophytic grasslands). The measure of population size is not practical for manytaxa above all in islands that often have sectors of difficult access (e.g. sea cliffs).Lists and distribution mapping of taxa are probably the most commonly usedsurrogate for overall biodiversity at both local and broader scales. The specieslevel is an accepted standard, because the concept of species is well understoodalso by the public, and policy makers. Information on the presence of higherplants is available for many Mediterranean islands due to records of visiting naturalists,and formal surveys undertaken by governments and NGOs (e.g. thePIM initiative). In addition, in the islands the lack of records of a species is moreeasily correlated to its disappearance from that territory than it is in the mainland.Anyway, particular attention has to be put on measurements of rarity andextinction risk. Most extinctions, after a first peak due to a specific phenomenon,have a long after-effects, whereby the species may persist at low numbers witha negligible chance of recovery and a severely diminished role in the ecosystem.