Krakatau: genetic consequences of island colonization

Abstract

This research has examined the genetic consequences of colonization in five tree species on the Krakatau islands, Indonesia after habitat had been destroyed over a century earlier by extreme volcanic events. The Krakatau islands provide a unique, well-documented example of island colonization in the tropics. The islands are continental and lay approximately midway between Java and Sumatra; the nearest points on these landmassess to the islands being approximately 41 and 31 km, respectively. Currently the islands are covered in species poor, early seral monsoonal forest that is little disturbed by humans. With the increasing levels of habitat destruction occurring in the tropics due to human mediated environmental degradation, it is important to understand the processes involved in ecosystem restoration. This is the first study to use genetic markers to examine the genetic consequences and patterns of colonization on these islands. The final conclusions of this study are these: Species dispersal ability, distance to the islands, island positioning and ecological factors are all important in structuring genetic diversity. Species with high dispersal ability maintain higher levels of genetic diversity within populations and lower levels of differentiation between populations relative to species with poorer dispersal ability. Dispersal ability alone was not a good predictor for the effect of colonization on genetic diversity within populations as other ecological factors are also important in structuring genetic variation. Counter to expectation, most of the study species maintained equivalent or higher levels of genetic diversity on Krakatau relative to mainland sites and other islands in the Sunda Strait closer to the coast. Small plant population size and island isolation is thought to be an important factor leading to hybridization in some species.