Fragmentation and pollen movement in a Costa Rican dry forest tree species

Loss of natural habitat due to the development of once forested areas has left a mosaic of forest fragments and isolated trees within a matrix of open pasture and agricultural fields. Such habitat fragmentation may be detrimental to the genetic diversity, ecology, and community level interactions of once continuously distributed species. Since fragmentation will affect the distribution of most plant and animal species, the reproductive dynamics of small remnant populations 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. This study employed allozyme genetic markers to examine these effects on remnant populations 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. The information gained from such analyses will be an important component for the effective future management and the development of conservation strategies for tropical tree species in fragmented landscapes.