Post-dispersal fate of seeds dispersed by large primates is well studied but little is known about this process in small frugivores like tamarins. This study in the Amazonian forest of Peru aimed at investigating if characteristics related to the defecation patterns of tamarins (Saguinus mystax and Saguinus fuscicollis) affected short-term post-dispersal seed fate, through secondary seed dispersal by dung beetles and removal by seed predators. Data on dung beetle activity were based on direct observations of 49 defecations while seed fate was studied using semi-controlled experiments (N = 458 for secondary dispersal and N = 398 for predation). Tamarins produce small defecations with a low number of seeds. Thirty-five per cent of defecations were visited by an average of 1.5 dung beetles that usually transport the faeces as pellets. Twenty-four per cent of seeds were buried by beetles at a mean depth of 3.5 cm. With increasing quantities of faecal matter, the probability of secondary seed dispersal increased but not the depth of burial. Seed predation pressure was low (17.6%) after 4 d and higher in faeces of S. mystax than in faeces of S. fuscicollis. Despite their small size, tamarins could be considered as high-quality seed dispersers, with a potential role for forest regeneration.

The reproductive success of plants depends to a very large degree on the quantity and quality of seed dispersal. If dispersal is by animals (zoochory), characteristics of fruits such as colour, size, shape and nutritional content have been shown to influence the likelihood of visitation by frugivores or the rate of fruit removal (e.g. Fuentes 1994, Howe 1983, Murray et al. 1993). While these characteristics function in the attraction of dispersers, plants may also evolve characters that manipulate the behaviour or the physiology of dispersers after the consumption of fruits and the ingestion of seeds. An example of such post-consumption manipulation of dispersers' behaviour by plants is provided by mistletoes. The viscous mistletoe seeds stimulate the disperser (usually birds) to either rub the cloaca (when seeds are passed through the gastro-intestinal tract) or the bill (when seeds are regurgitated) on a branch (e.g. Reid 1991). It has also been proposed that fruits might manipulate the disperser's physiology by including laxatives that determine the optimal passage time through the disperser's gut (Murray et al. 1994), although this view has recently been challenged (Witmer 1996).