osystem. The scientists from the BDFF project point out one exception. Tamarins and marmosets, both species in need of protection , flourish in small tropical rainforest reserves because of the luxurian growth of early successional plant species, and the lack of large predators which are unable to exist in the smaller reserves. Certainly , a system of only small reserves would not suffice to protect the genetic heritage of biological diversity in the tropical rainforest, but a heterogeneous mosaic of large and small reserves may provide the best alternative. Although edge has typically been associated with an increase in species richness, researchers are increasingly documenting how edge effects negatively impact the native plants and animals. The BDFF researchers pointed out that although the number of species may be higher in edge that the adjacent interior habitat, species diversity is usually not. Diversity takes into account not only raw number of species, but the relative abundance of the species present. Another potentially adverse effect of edge is that it inherently reduces the size of the habitat interior because of the many physical changes which occur where and edge is compared to a human dominated area. Most documented cases of edge effects are from forest edges, so I will focus on them. In addition to the luxuriant growth of shade-intolerant vegetation at a forest edge in response to the increase in available light, a “seed rain” bombards the forest interior, often from introduced exotics. The increased exposure to wind causes a higher rate of treefalls and tree mortality, and temperature and humidity are quite different at the edge than in the forest interior. These physical changes affect the plants and animals of the habitat. Lovejoy and others, in the BDFF project in Brazil, found that the understory birds tend to avoid artificial edges. They found 38% fewer birds 10 meters from clearing than 5...
