The reproductive dynamics of small, remnant populations left in the aftermath of land development are likely to differ from those of large, continuous populations. Comparisons of population parameters such as genetic diversity and structure, as well as pollen flow, between populations of adults established prior to fragmentation and their post-fragmentation progeny make it possible to examine the effects of disturbance on the current reproductive dynamics of individuals established when landscapes were different. We empolyed allozyme markers to examine these effects over two reproductive episodes in remnant popualtions (N=3-35) of Enterolobium cyclocarpum, a dominant tree species commonly found throughout highly disturbed areas of Guanacaste Province, Costa Rica. Moreover, direct estimates of effective population sizes and rates of pollen immigration allowed predictions of the effects of genetic drift and inbreeding on the genetic composition of future generations of these fragment populations. Comparisons of the genetic structure of adult populations (GST = 0.058) to pollen gametes in 1994 and 1995 (GST = 0.053 and 0.115, respectively) suggest an increased genetic differentation of pollen gametes compared to adults in 1995. Pollen immigration (m) remains substantial at distances of 1 km and fairly equivalent gamete production in both years produced only moderate reductions in Ne relative to census population sizes. Direct estimates of m and Nev allowed us to predict moderate effects of genetic drift and inbreeding on the genetic composition of future population (Nevm = 0.55 - 1.79) and (FST = 0.114 - 0.311) even in a worst case scenario (N=3). The information gained from such analyses will be an important component for the effective future management and the devlopment of conservation strategies for tropical tree species in fragmented landscapes.

Key words: Effective population Size, Enterolobium cyclocarpum, Genetic Consequences, Genetic Structure, Pollen Flow, Tropical Dry Forest Fragmentation