The irreplaceable role of surviving megafauna in long-distance seed dispersal: Evidence from an experiment with Neotropical mammals

The downsizing of disperser assemblages by selective defaunation is a
worldwide phenomenon thought to have important consequences in
animal-dispersed plants. Numerous large-seeded Neotropical plants
currently depend on the last megafaunal survivors, the large tapirs
Tapirus spp., and medium-sized frugivores. The extent to which medium
frugivores are functionally equivalent to tapirs remains unresolved. We
combined feeding trials, seed dispersal kernel modeling based on seed
retention times and animal movement simulation (Levy walks), and
germination experiments in a large-seeded palm to assess the dispersal
quality provided by the largest (tapirs) and two medium (foxes and howler
monkeys) frugivore species in terms of dispersal distances and gut passage
effects on germination. Tapirs retained the seeds in the gut for much
longer (mean=221 hours) than howlers (43 h) and foxes (22 h). Median
dispersal distance by tapirs (1252 m) was 14 and 40 times larger than that
by foxes (88 m) and howlers (31 m), respectively. The seed dispersal
kernel of tapirs showed a 5th percentile value (291 m) larger than the
95th percentiles of foxes (285 m) and howlers (108 m). Manually depulped
and gut-passed seeds germinated in similar proportions, showing,
respectively, 3.5 and 2.5―2.9 times higher values than intact fruits.
Germination probability and seed viability decreased with retention time
in howlers’ and tapirs’ gut, with howlers showing a steeper negative
relationship. Such detrimental effect implies a trade-off between
germination success and dispersal distance. We conclude that tapirs may
not play a unique role in germination enhancement but move seeds much
further than medium frugivores, thus playing a critical role as
long-distance dispersers of many plants. This study provides important
insights on palm–frugivore interactions and the potential consequences for
large-seeded plants of losing the last megafaunal representatives in the
Neotropics.