Historical processes and environmental factors as determinants of inter-island differences in endemic faunas: the case of the Balearic Islands

Aim We describe current interisland similarities of endemic faunas, and elu cidate the significance of historical factors and environmental ones in det ermining the pattern found. Location The six major islands of the Balearics (Western Mediterranean). Methods An extensive review of all the endemic fauna ranging from platyhelm inthes to mammals is made. From 568 presumed endemic species and subspecies , 230 full species with neither taxonomic nor distributional uncertainty ar e chosen. Inter-island similarities are determined using such a presence-ab sence matrix. Finally, relationships between the matrix of faunistic simila rity and a number of matrices measuring environmental and historical factor s are elucidated. Results Endemic fauna similarities depend clearly on historical factors. De pendence on environmental factors is unclear. Moreover, endemic fauna revea ls two clear-cut clusters of islands within the Balearics: the Gymnesic Isl ands, in the NE, and the Pityusic Islands in the SW. Historical factors clu ster the Balearic Islands in the same way. Contrasting, environmental varia bles show smoothed, no significant differences among the Gymnesics and the Pityusics. Main conclusions Pre-human flora (palynology) and fauna (bird and mammal fo ssil record) suggest that environmental differences among the Gymnesics and the Pityusics have now been reduced in comparison to the environmental dif ferences at the Pleistocene and Holocene boundary. This environmental homog enization is likely related with human invasion. Historical effects of preh uman differences between Gymnesic and Pityusic Islands are still recognizab le on endemic fauna. In contrast, there is no historical effects on interis land similarities using currently breeding birds las an example of organism s well-dispersed and related to vegetation type). We explain the pattern of interisland similarities of endemic fauna as the result of the independent histories among the two islands groups. Contrasting, successive colonizati ons and extinctions would determine interisland similarities of breeding bi rds.