The effectiveness of a seed disperser is assessed by the quantity (number of visits to fruiting trees and number of seeds dispersed) and quality of dispersal (seeds passed through the gut unharmed and how and where the seeds are dispersed). This is the first study to examine quantitative and qualitative aspects of seed dispersal by golden lion tamarins

The influence of the golden lion tamarin (Leontopithecus rosalia) as a seed disperser was studied by monitoring two groups of tamarins from December 1998 to December 2000 (871.9 hours of observations) in a forest fragment in south-east Brazil. The tamarins consumed fruits of 57 species from at least 17 families. They ingested the seeds of 39 species, and 23 of these were put to germinate in the laboratory and/or in the field. L. rosalia is a legitimate seed disperser because the seeds of all species tested germinated after ingestion, albeit some in low percentages. These primates do not show a consistent effect in final seed germination, because they benefit some species while damaging others. Feces were examined for seeds that had been preyed upon or digested.

Frugivores, as seed dispersers may influence the spatial patterns of adult and juvenile plants, but a large portion of the potential recruitment of plant populations is lost to seed predators. The majority of seeds dispersed by primates are killed by seed predators or moved by secondary dispersers. Little is known about post-dispersal seed-predation and seedling distribution of exploited plant species. This study iinvestigated the survival and establishment of seedlings from seeds defecated by the golden lion tamarin ( Leontopithecus rosalia), a frugivorous endemic primate of the Atlantic Forest of Brazil. Two groups of golden lion tamarins were studied in the União Biological Reserve from April 2003 to March 2004. Seeds from fruits consumed by tamarins and collected from their feces were evaluated with respect to the following: germination success, seed disappearance or secondary dispersal on the forest floor, seed predation, and seedling establishment and survival for the length of the study period. The tamarin groups consumed 88 fruit species. Of these, 38 were used to run 107 experiments which indicated that more than 50% of the seeds disappeared, about 15% died before germinating and seeds of 22 species reached the seedling stage. At the end of the study, only 15 of these species still had surviving seedlings. Studies on seed fate are important for understanding the role of the golden lion tamarind in the natural process of forest regeneration in the lowland Atlantic Forest of the state of Rio de Janeiro in Brazil.