REPRODUCTIVE AND GENETIC CONSEQUENCES OF FOREST FRAGMENTATION - 2 CASE-STUDIES OF NEOTROPICAL CANOPY TREES

Large areas of continuous tropical forests are rapidly becoming fragme nted as a result of human activities, prompting a growing need for inf ormation on the reproductive and genetic responses of free species to disturbance, Here we review the literature on pollen dispersal in cont inuous forest stands in order to identify factors expected to enhance or to inhibit interfragment pollen flow, We then describe two empirica l studies of the effects of fragmentation on pollen flow in Neotropica l populations of Spondias mombin (Anacardiaceae) and five monoecious s pecies of Ficus (Moraceae). In S, mombin, small fragment populations s uffered significant reductions in germination rate and fruit productio n relative to large fragment and continuous Sorest populations, Nevert heless, 90-100% of the progeny produced in the small fragments were th e product of pollen gene flow originating from forest stands located o ver 80-1000 m away, In contrast. to S. mombin, which is relatively abu ndant and pollinated by a variety of small insects, the strangler fig species studied were relatively rare and pollinated by species-specifi c wasps that are both small and short-lived, Paternity analyses reveal ed these highly coevolved pollinators to be effective agents of pollen movement over very long distances, routinely dispersing 6-14 km to re ceptive host trees, Because of such extensive pollen flow, breeding po pulations of figs were estimated to consist of hundreds of intermating individuals distributed over 108-632 km(2), an area substantially lar ger than has been documented for any other plant species, The observed patterns of dispersal in S. mombin and Ficus demonstrate the potentia l for ecologically and evolutionarily significant pollinator and polle n movement among populations occurring in both disturbed and continuou s forest environments. Moreover, given the integral relationship of fi gs, as keystone plant resources, to other plant and animal species, th e extensive spatial scale of fig breeding units demonstrates how the c onservation of biodiversity in spatially isolated reserves may be depe ndent on the preservation of forest elements in a surrounding fragment ed landscape.