Talk, Jahrestreffen des AK Biogeographie im Verband der Geographen an Deutschen Hochschulen (VGDH), Bayreuth: 2009-05-15 - 2009-05-16
Abstract:
The Canary Islands are a place of pilgrimage for ecologists since the time of Alexander von Humboldt and Charles Darwin. Even though there is still some debate on the taxonomic status of some endemic species, there exist excellent quality of biotic data that can be used for biogeographical analyses. Here, we use this data to address a recent debate on the influence of species richness and time on speciation on oceanic volcanic island archipelagos: 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. 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.