Gut passage effect of the introduced red-whiskered bulbul (Pycnonotus jocosus) on germination of invasive plant species in Mauritius.
In Mauritius, many of the worst invasive plant species have fleshy fruits and rely on animals for dispersal. The introduced red-whiskered bulbul (Pycnonotus jocosus) feeds on many fleshy-fruited species, and often moves from invaded and degraded habitats into higher quality native forests, thus potentially acting as a mediator of continued plant invasion into these areas. Furthermore, gut passage may influence seed germination. To investigate this, we fed fleshy fruits of two invasive plant species, Ligustrum robustum and Clidemia hirta, to red-whiskered bulbuls. Gut passage times of seeds were recorded. Gut-passed seeds were sown and their germination rate and germination success compared with that of hand-cleaned seeds, as well as that of seeds in whole fruits. Gut passage and hand-cleaning had significant positive effects on germination of both species. Gut-passed seeds of both C. hirta and L. robustum germinated faster than hand-cleaned seeds. However, for L. robustum, this was only true when compared with hand-cleaned seeds with intact endocarp; when compared with hand-cleaned seeds without endocarp, there was no difference. For overall germination success, there was a positive effect of gut passage for C. hirta, but not for L. robustum. For both C. hirta and L. robustum, no seeds in intact fruits geminated, suggesting that removal of pulp is essential for germination. Our results suggest that, first, the initial invasion of native forests in Mauritius may not have happened so rapidly without efficient avian seed dispersers like the red-whiskered bulbul. Second, the bulbul is likely to be a major factor in the continued re-invasion of C. hirta and L. robustum into weeded and restored conservation management areas.