Interactions between sympatric species are of particular interest for understanding the mechanisms that allow animal coexistence in the ecological community. The mantled howler monkey (Alouatta palliata Gray) and the white-nosed coati (Nasua narica Linnaeus) are similar-sized mammals with a sympatric distribution in the Neotropics (Nowak 1999). Since these two species are partly frugivorous (howler, Crockett & Eisenberg 1987; coati, Gompper 1997), and fruit is often limited (Laurance et al. 2003), howlers and coatis might be observed foraging from the same fruiting tree, but there is no information regarding this possibility. We studied the feeding encounters between these two species in a small forest fragment, and discuss the conditions under which these episodes occur.

We studied changes in germination rates and dispersal distance of seeds of Ficus perforata and F. lundelli dispersed by howler monkeys (Alouatta palliata mexicana), in a small (40 ha) ‘disturbed’ and a larger (>600 ha) ‘preserved’ tropical rainforest in southern Veracruz, Mexico. The interaction between A. p. mexicana and Ficus (Urostigma) spp. is beneficial for the interacting species and has important implications for their conservation. Howler monkeys gain from the ingestion of an important food source, germination rates of Ficus seeds are improved by passage through the monkeys' digestive tract, and the seeds are more likely to be deposited in a site suitable for germination and development. Seed dispersal distances are relatively larger in the preserved site, with both the size of the forest area and the spatial pattern of Ficus affecting the dispersal process. In a large forest fragment with ‘regularly’ distributed Ficus individuals the howler monkeys move away from the seed source, increasing the probability that the seeds are desposited on a tree other than Ficus, which is important for the germination and future development of a hemiepiphytic species. In a small forest fragment with trees distributed in clumps howlers repeatedly use the same individual trees, and faeces containing seeds may be dropped on unsuitable trees more often. These are key issues when addressing conservation policies for fragmented forests.