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

Oceanic islands, due to their evolutionary history and isolation, play a
dual role of having high endemicity and being 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
Narcondam, a remote oceanic island. The island endemic Narcondam Hornbill
(Rhyticeros narcondami) was the sole seed disperser of
the palm (90 hours; N = 15 trees), with mean (±
SE) visitation rate being 0.23 (± 0.06) individuals per hour and fruit
removal rates of 3.5 (± 1.5; range: 0–16) fruits per visit, indicating a
lack of redundancy in seed dispersal of the palm on this island. Whereas
the invasive
rodent, Rattus cf. tiomanicus, was the
sole predator of palm seeds (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 indicates density-independent seed
predation and the lack of safe regeneration sites for Caryota
mitis, with potential deleterious effects on 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 of an invasive rodent.