Dissertation Research: Gene Flow and the Scale of Fragmentation in Tropical Tree Populations

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DEB 95-20702 Hamrick Deforestation is occurring at an alarming rate in many parts of the world, especially in tropical regions. Much attention has been focused on the resultant loss of species diversity, particularly of animals. Relatively little effort has gone into examining the effects of fragmentation on the dynamics of tropical tree populations. In contrast to the temperate zone, most tropical tree species disperse pollen and seeds by means of animal vectors. Thus, it is likely that habitat fragmentation could seriously impact the integrity of tropical tree populations if pollinator and seed disperser associations are disrupted. A lack of dispersal among remnant forest fragments would lead to genetic differentiation among fragments over several generations and an increased probability of extinction due to demographic factors associated with small population size. This combination of factors should lead to a loss of genetic diversity in the species over time which could compromise its ability to respond to future evolutionary pressures. This study examines the effects of habitat fragmentation on gene movement via pollen and seed within and among remnant forest patches in premontane tropical rain forest in southern Costa Rica. The study site consists of a 20 hectare fragmented area including three one-hectare remnant patches plus two one-hectare plots in continuous forest for control. Molecular genetic markers will be utilized to identify adults and young seedlings of the study species occurring within the study sites. Genetic fingerprints will be used to establish patterns of parental relationship between seedlings and parent-pairs occurring within the study region. Seedlings that cannot be produced by parents resident on the plot represent instances of long-distance gene flow. The detailed examination of parent-seedling associations within the study regions will provide important evidence regarding: the amount of genetic connectedness among patches; the importance of f ree-standing individuals in pastures to the local dynamics of patch populations; and the importance of corridors to the movement of pollen and seeds. These data will provide an empirical perspective on patterns of gene flow in a heterogeneous environment and will prmvide necessary information for the conservation of tropical areas and the design of tropical reserves.