Bachelor Thesis

Plant differentiation on oceanic archipelagos in dependence of island age.

Bernd Lenzner (09/2011-11/2011)

Support: Manuel Steinbauer, Carl Beierkuhnlein

The “general dynamic model of island biogeography” (GDM), provided by Whittaker et al. (2008) developed to become the current, widely accepted theoretical concept within island biogeography. Its aim is to describe general biotic patterns within oceanic archipelagos.
Within this study, it will be tested, whether some of the predictions derived from the GDM can be supported at a taxonomic higher level. Therefore, four different plant families (Asteraceae, Lamiaceae, Fabaceae and Poaceae) within six oceanic archipelagos (Azores, Canaries, Cape Verde, Galápagos, Hawai’i and Marquesas) have been analyzed.
Following Whittaker et al. (2008) the number of Singles Island Endemics (nSIE) as well as the percentage of Single Island Endemics (pSIE), were investigated to determine the speciation processes within the plant families in dependence of the geological ages of the islands, within the archipelagos, and in dependence of the respective island areas. Hence, I used linear mixed effect modeling to test the statistical approach (the logATT² model) gained from the GDM.
My analysis showed, that applied on a taxonomic higher level the logATT² model does not provide the most parsimonious approach for island biogeographical patterns. In contrast to the expected hump-shape pattern, my research produced two types of trends. One, where highest nSIE occurred nearly from the beginning leading to the conclusion that rapid speciation might be involved. And second, the case, where the nSIE increases with island age. Hence it can be concluded, that an overlay of these two types leads to the hump-shape pattern when observing all occurring plant families. Nevertheless, does the framework provided within the GDM, leave enough freedom for interpreting the obtained results.