Primate Seed Dispersal: The Fate of Dispersed Seeds

The three primate species of Santa Rosa National Park, Costa Rica (Ateles geoffroyi, Alouatta palliata, Cebus capucinus) have diets in which fruits are major components. All three primate species defecated seeds of many fruiting species; the majority of which (60%) germinated under experimental conditions. The sampling of seed traps placed throughout he forest indicated that, on average, 392 large seeds that passed through the stomachs of monkeys fell weekly per hectare of forest floor. However, the dispersal performed by the primates may not be the final stage of dispersal for many of these seeds. By constructing artificial dung piles containing seeds it was shown that 51.8 percent of the seeds were either removed by secondary dispersers, or killed by seed predators within 5 days of being placed in the forest. The rate of seed removal varied depending on the seed species. QUANTITATIVE STUDIES AND THEORETICAL DISCUSSIONS of seed dispersal have concentrated on dispersal of seeds by birds and bats (Snow 1965, 1971; McDiarmid et al. 1977; Fleming & Heithaus 1981; Fleming 1982; Heithaus 1982; Herrera 1982, 1984, 1985). However, in tropical forests, primates constitute b tween 25 percent and 40 percent of the frugivore biomass (Eisenberg & Thorington 1973, Eisenberg etal. 1979, Terborgh 1983), and they defecate large numbers of viable seeds (Hladik & Hladik 1969, Cant 1979, Estrada & Coates-Estrada 1984, 1986). Most studies of seed dispersal report observations on which animals removed fruit from a particular fruiting tree, the removal rate, and in some instances, whether or not the injested seeds are viable when voided. Such studies only examine the very initial stage of seed dispersal and do not examine the quality of the location where the seeds are deposited. Not addressing this issue may produce misleading results (Janzen 1983). In addition, by not documenting the initial fate of seeds deposited on the forest floor, it is not possible to assess the relative importance of primary dispersers versus animals that subsequently move or kill the seeds (Estrada & Coates-Estrada 1986, Janzen 1986a). The objective of this investigation is to describe seed dispersal ssociated with the three species of primates in Santa Rosa National Park, Costa Rica, and document the initial fate of the dispersed seeds under various natural and experimental conditions.