Implications of seed dispersal by animals for tropical reserve management

Many tropical trees bear fruits adapted for consumption by animals, and many tropical animals depend on fruits for food for at least part of the year. The purpose of this paper is to discuss the potential importance of: (1) uneven species abundance distributions; (2) the imperative of local seed dispersal for plant recruitment; and (3) seasonality of fruit production for managing small tropical reserves. Some mutualistic seed-dispersal systems are ‘pivotal’ for forest communities. Although most species of trees produce when other fruits are readily available in the forest, others (e.g. Casearia corymbosa in Costa Rican rainforest and Virola sebifera in Panamanian rainforest) bear fruits during annual periods of fruit scarcity, and consequently maintain species of fruit-eating birds and mammals which are critical for the dispersal and ultimate recruitment of many tree species at other times of the year. The question of relative abundance presents particular problems when ‘pivotal’ plant species are rare or confined to special habitats. This paper considers ecological relationships which accelerate species loss from habitat islands over and above ‘random’ loss of ecologically independent species predicted from biogeographic theory, and suggests management methods that can reduce such excessive loss.