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 5^th percentile value (291 m) larger than the 95^th 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.