Speciation of endemic plants in oceanic islands

Tod STUESSY (Wien): Oceanic islands offer special opportunities for understanding patterns and processes of evolution. The availability of molecular markers during recent decades has enhanced these opportunities by revealing genetic divergence and speciation within island systems. The types and degrees of genetic modifications that occur are due to many factors. The age of the island is extremely important because oceanic islands subside on their submarine plates over time, and erosion due to wind, rain, and wave action grinds down soft volcanic substrates. These geomorphological events can dramatically impact population number and size, and hence levels of genetic diversity. The mode of speciation is also of significance. With anagenesis genetic variation accumulates through time, whereas with cladogenesis the gene pool splits into populations of adaptively radiating species. Breeding systems, population sizes, and generation times are also important, as is hybridization between closely related taxa. Human disturbance has affected plant population number and size through the harvesting of forests and the introduction of invasive plants and animals. Explanation of observed levels of genetic variation within species of oceanic islands, therefore, requires consideration of many interconnected physical, biological, and anthropomorphic factors.