Frugivory and seed predation of fishtail palm (Caryota mitis Lour.) on the remote oceanic island of Narcondam, India

Abstract

Oceanic islands, due to their evolutionary history and isolation, hold a disproportionately high proportion of endemic species. However, their evolutionary history also makes them vulnerable to extinctions, with most known extinctions occurring on islands. Plant-animal interactions are particularly important on islands, as island systems generally have low redundancy and are more vulnerable to disruption either via extinction or by invasive species. Here, we examined the fruit removal and seed predation of a keystone palm, Caryota mitis, on the remote oceanic island of Narcondam. The island endemic Narcondam hornbill (Rhyticeros narcondami), was the sole seed disperser of the Caryota mitis (90 hours; N = 15 trees), indicating a lack of redundancy in seed dispersal of the palm on this island. While the invasive rodent, Rattus cf. tiomanicus was the sole predator of the Caryota mitis seeds in the forest (N = 15 individual fruiting palms, 416 trap nights). Overall, 17.1% of the seeds placed (N = 375 seeds) were removed. Seeds placed under and away from the canopy, and at different densities (2 plots with 10 seeds each; 1 plot with 5 seeds, respectively), showed similar removal rates. This is indicative of ambient seed predation and the lack of safe sites for the regeneration of Caryota mitis, with potential deleterious effects on the subsequent stages of the "seed dispersal cycle". Here, from a data deficient site, we provide baseline information on the plant-frugivore interaction of a keystone palm and the potential impacts by an invasive rodent.