Is there really more biodiversity in Mediterranean forest ecosystems?

The Mediterranean Basin accounts for more than 10% of the world's vascular plant biodiversity in an area less than 1.5% the size of continental Earth. Forest tree taxa are also exceptionally diverse: more than 100 species have been recorded around the Mediterranean, but less than 30 species can be found in Temperate Europe. This amazing biodiversity was developed over millions of years due to the highly heterogeneous geology and climate of the Mediterranean. Did these factors also affect biodiversity within species, i.e., the genetic diversity of populations? Heterozygosity (the within-population gene diversity), and differentiation (the among-population spatial genetic structure), of neutral genes (isozymes) were used to measure within-species biodiversity in four conifer genera commonly found in the Mediterranean: Abies Mill., Cedrus Trew, Cupressus L., Pinus L. Their within-species biodiversity was significantly higher than that of other conifer species worldwide and did not correspond to expected values in terns of biogeography or levels of endemism. Gene diversity was significantly higher in the Eastern than in the Western Mediterranean Basin, and, surprisingly, was only mildly affected by human impact. A specific post-glacial recolonization model is proposed for the Mediterranean Basin, in which effective glacial refugia are more numerous, and genetic drift is less, than what is proposed for Europe. The within-species approach to biodiversity can help solve taxonomic questions, and when used as an indicator of evolutionary potentials, is an essential component of conservation strategies.