The ecological effects of logging in the tropics have been analysed largely in terms of its impacts on species diversity and abundance. However, information is very limited regarding the impact of logging on ecological processes such as species interactions. Here we hypothesize that timber extraction per se, that is, in the absence of hunting, affects the abundance of the frugivorous spider monkey, Ateles geoffroyi, and that this has indirect effects on the recruitment of a predominant tree species, Manilkara zapota, and the diversity of the understorey plant community. We compared logged and unlogged sites, using a paired design. In each management condition we conducted line transects and interviews to evaluate spider monkey abundance and game preferences, respectively. Impact on plant recruitment and understorey diversity were evaluated using 2 × 2-m plots (N = 320) established under 40 M. zapota tree crowns. No spider monkeys were recorded in logged sites whereas they were abundant (15 ± 8 individuals per man-km) in unlogged sites. Interviews showed that spider monkeys are not hunted by local inhabitants. Logging was correlated with a reduction of the number of M. zapota fruits used by A. geoffroyi; an increase in the number of sites dominated by M. zapota; and a reduction in understorey plant diversity. Our results suggest that the absence of A. geoffroyi in logged sites can indirectly impact plant recruitment and diversity via the disruption of plant–frugivore interactions. Further work is needed to assess if these effects persist over the long term, to define if logging operations affect the overall diversity of tropical forests.

Spider monkeys (Ateles geoffroyi) detect sucrose at a threshold lower than any primate yet tested and prefer sucrose to glucose or fructose in laboratory tests. This preferential selection of sucrose led to the hypothesis that such acute discrimination is related to a diet of sucrose-rich fruits. Furthermore, it has been suggested that fruit sugars may be related to distinct guilds of vertebrate seed-dispersers. The objectives of this study were: (1) to test if spider monkeys select sucrose-rich fruits both within and among plant species and (2) to test the hypothesis that sugar concentration is related to bird, bat or monkey seed-dispersal syndromes. Data were collected from one troop of spider monkeys in south-western Costa Rica. Interspecific comparison of ingested fruits shows that spider monkeys consumed species with significantly higher concentrations of glucose and fructose than sucrose. Similarly, at the intraspecific level, food-fruits had significantly more fructose and glucose than non-food fruits, but no difference was found for sucrose. The three different sugar types were not correlated with the importance of the species in the diet based on the amount of time they spent consuming each species. Although sucrose concentrations were significantly higher in primate-dispersed species compared with those dispersed by other vertebrates, soluble carbohydrates in primate-dispersed fruits were principally composed of glucose and fructose. Neither fructose nor glucose concentrations showed significant differences across the three categories of seed dispersal.