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Background and Aims Archipelagos are unique systems for studying evolutionary processes promoting diversification and speciation. The islands of the Mediterranean basin are major areas of plant richness, including a high proportion of narrow endemics. Many endemic plants are currently found in rocky habitats, showing varying patterns of habitat occupancy at different spatial scales throughout their range. The aim of the present study was to understand the impact of varying patterns of population distribution on genetic diversity and structure to shed light on demographic and evolutionary processes leading to population diversification in Crepis triasii, an endemic plant from the eastern Balearic Islands. Methods Using allozyme and chloroplast markers, we related patterns of genetic structure and diversity to those of habitat occupancy at a regional (between islands and among populations within islands) and landscape (population size and connectivity) scale. Key Results Genetic diversity was highly structured both at the regional and at the landscape level, and was positively correlated with population connectivity in the landscape. Populations located in small isolated mountains and coastal areas, with restricted patterns of regional occupancy, were genetically less diverse and much more differentiated. In addition, more isolated populations had stronger fine-scale genetic structure than well-connected ones. Changes in habitat availability and quality arising from marine transgressions during the Quaternary, as well as progressive fragmentation associated with the aridification of the climate since the last glaciation, are the most plausible factors leading to the observed patterns of genetic diversity and structure. Conclusions Our results emphasize the importance of gene flow in preventing genetic erosion and maintaining the evolutionary potential of populations. They also agree with recent studies highlighting the importance of restricted gene flow and genetic dr

Classical metapopulation (CM) theory considers that species persistence in the landscape depends on a turnover of extinction-(re)colonisation of suitable habitat patches at each generation. Therefore, metapoputation dynamics are approximated by binary changes in the state of individual patches. This approach has allowed rigorous mathematical analyses of metapopulation dynamics, establishing links with general laws in ecology or deriving operational concepts in conservation biology. However, a critical review of the literature shows that only a few spatially structured populations function according to CM theory. Moreover, empirical studies of CMs usually focus on species (1) at the margin of their distribution range, (2) with small or extremely small local population sizes and (3) declining in the study area (expanding in one case). Such non-equilibrium population systems are far from the equilibrium world idealised in CM models. Furthermore, empirical comparisons of metapopulations in highly fragmented landscapes show that extinction-(re)colonisation dynamics match those predicted by the theory only when local populations are very small. The lack of correspondence between CM theory and the real, natural world may explain why models and concepts derived from the theory are not used in population viability analysis or conservation strategies. The final message of this paper is three-fold: (1) exclusive, implicit assimilation of spatially structured populations to CMs should be avoided, (2) attempts to manage any population using CM theory should be preceded by careful examination of the correspondence between the field situation and assumptions of the theory (particularly regarding the high rate of local population turnover and the equilibrium state of the metapopulation) and (3) theorists should avoid to present CM theory and derived concepts as the only conservation framework for populations confronted with habitat loss and fragmentation. (C) 2004 Elsevier GmbH. Al