Endozoochory by goats and white-tailed deer: type of ruminant affect recovery and germination of Neltuma pallida seeds

Abstract

The "algarrobo" (Neltuma pallida) is a key tree species in the seasonally dry tropical forests in Equatorial Pacific coast of South America, currently at risk. Its regeneration depends on endozoochorous dispersal, in which seeds are ingested and later defecated by animals, helping to release and scarify them. We compared the role of the native white-tailed deer (Odocoileus virginianus peruvianus) and the introduced goat (Capra hircus) in seed dispersal. Seeds were recovered from the dung of both species after experimental feeding and from grazing goats in a fruiting N. pallida forest. Seed recovery was higher in deer dung (9.34%) than in goat dung (3.06%), and retention time was shorter in deer than in goats (peak at 48 and 84 h respectively). Only passage of seeds through the deer's digestive tract significantly improved cumulative germination (63% vs. 44%) and germination rate (time to reach 25% germination, T25 = 8.98 days). Meanwhile, the passage of seeds through the goat's digestive system reduced germination rate under experimental conditions (T25 = 19.25 days) but slightly increased it under forest conditions (T25 = 12.81 days), where goats ingest fruits constantly. Differences in seed recovery and germination are explained by the morphophysiological traits of ruminants. In conclusion, both goats and deer contribute to seed dispersal. White-tailed deer enhances seed germination (~66%), whereas goats maintain seed viability (~44%) and exhibit a longer seed retention time. During peak fruiting, alternating grazing between high-fruiting and degraded areas is recommended to maximize seed incorporation into the soil.