Goats foster endozoochoric dispersal of exotic species in a seasonally dry tropical forest ecosystem

摘要

Goats at high densities are known to degrade vegetation in arid environments around the world. Their role as potential dispersers of seeds of native and exotic plant species, however, still remains uncertain. This study assesses whether goats, through endozoochorous seed dispersal, may potentially change the plant assemblage of seasonally dry tropical forests. We used seedling emergence as a method to analyze which plant species germinated from goat feces and thus may be dispersed by goats after passing through their intestinal tract. Seedling emergence data were analyzed with respect to the plot vegetation, water availability (permanent, temporary and no water courses), and altitude (as an indicator of anthropogenic pressure). We identified 18 species belonging to 14 families. Feces from the plots near permanent water with the largest anthropogenic pressure were characterized by the highest number of germinated plants. The most common plant species by far found in the experiment was the exotic Prosopis juliflora. This high abundance of P. juliflora seedlings shows that non-native grazers facilitate the spread of exotic plant species in threatened dry forest habitats. We therefore conclude that free-roaming goats may play an important ecological role in changing plant species assemblages of even remote areas.