Direct and indirect effects of frugivorous monkeys on seed dispersal and germination in native and non-native plants of southwest Puerto Rico

The effectiveness of two naturalized frugivorous monkey species, Macaca mulatta and Erythrocebus patas, was evaluated to determine if they function as seed dispersers in their “new” habitat.  For the past 30 years these monkeys have formed permanent colonies on and around the slopes of the Sierra Bermeja, an area of high species endemism in the southwest of Puerto Rico.  Monkeys may: 1) directly benefit native plants by dispersing their seeds, 2) indirectly benefit native plants by digesting the seeds of non-native plants, 3) directly harm native plants by digesting their seeds, or 4) indirectly harm native plants by dispersing the seeds of non-native plants.  Seeds found in fecal samples were identified by comparing them to the seeds from plant samples fruiting during the study period.  Preliminary results from twenty-two fecal samples collected from September to November 2006 indicate that seeds of non-native plants are four times as frequent as the seeds of native plants.  Results of seed germination experiments are pending and will be used to provide insight as to whether dispersed seeds will germinate.  In addition, transects to determine relative plant densities will be used to determine if the proportion of native versus non-native seeds found in fecal samples reflect the density of native and non-native plants available to monkeys in the local environment.