Poster, 39. Jahrestagung der Gesellschaft für Ökologie (GfÖ), Bayreuth: 14.09.2009 - 18.09.2009
We discuss three drivers for speciation on oceanic volcanic island archipelagos using elevation explicit data from the Canary Islands: As a consequence of erosion processes oceanic islands usually shrink in altitude when aging. Differentiating the influence of elevation as an indicator for habitat diversity and island age as an indicator for the time available for speciation is therefore no trivial task. In addition, geographic distance to source ecosystems will reduce species immigration and will thus enhance niche occupation and speciation. Furthermore species richness might promote speciation through intensified inter-species competition leading to extinction and genetic adaptation. We use the percentage of single island endemic species (pSIE) in five different zonal ecosystems (distributed in altitude) on the Canary Islands, as an indicator for speciation. We test if speciation is increasing with altitude due to stronger ecological isolation of high elevation ecosystems on oceanic islands in the case of a low elevation species source region on the mainland. We find pSIE to be increasing with elevation. At mid altitudes, we identify a second maximum in the thermophilous woodland. We conclude that the high elevation ecosystems are ecologically isolated but surprisingly the altitudinal belt with strongest human influences has the highest values of pSIE, indicating intensive speciation there.