Cumulative germination of seeds ingested by black howler monkeys

Premise of the Study: Primates are important seed dispersers, especially
for large-seeded (> 1 cm length) tropical species in continuous and
fragmented rainforests. Methods: In three forest fragments within the
Montes Azules Biosphere Reserve, southern Mexico, we investigated the
effect of howler monkeys´ (Alouatta pigra) gut passage on the germination
rate and maximum germination (%) of native large-seeded species. One group
of howler monkeys, per fragment, was followed and fresh feces collected.
Large seeds were removed to compare their germination success with
non-ingested seeds of the same species collected underneath parent plants.
Results: Feces contained large seeds from seven tree species and one liana
species: Ampelocera hottlei, Castilla elastica, Dialium guianense,
Garcinia intermedia, Pourouma bicolor, Spondias mombin, Trophis racemosa
and the liana Abuta panamensis. Except for G. intermedia, ingested seeds
showed significantly greater germination rates than non-ingested seeds.
Non-ingested seeds of D. guianense showed negligible germination.
Regarding maximum germination, ingested seeds of D. guianense, P. bicolor,
S. mombin, T. racemosa and A. panamensis showed significantly greater
germination percentage; while G. intermedia showed significantly lower
germination percentage and no effect of seed ingestion was observed on A.
hottlei and C. elastica. Conclusions: In general, seed ingestion by howler
monkeys confers greater germination rates than non-ingested seeds. Greater
germination rates reduce predation probabilities and increases seedling
establishment in forest fragments. Primate dispersal services contribute
to germination heterogeneity within plant populations of old-growth forest
species and to their persistence in forest fragments.