Removal of Seeds from Horse Dung by Tropical Rodents: Influnce of Habitat and Amount of Dung

Abstract

Horses are major contemporary dispersers of guanacaste tree seeds (Enterolobium cyclocarpum) in Costa Rica, and probably were in prehistoric times as well. By placing 2—L and 8—L piles of fresh horse dung containing 5, 125, or 500 guanacaste seeds each in grassland and adjacent deciduous forest (Santa Rosa National Park, Costa Rica) I determined that (1) the seeds have a much greater chance of being harvested by seed predator rodents (Liomys salvini) from the dung in forest than that in adjacent grassland, (2) and 8—L seed—rich dung pile hides a larger absolute number of seeds from rodents than does a 2—L seed—rich dung pile, (3) a seed has a much greater chance of being harvested from a seed—rich dung pile than from a seed—poor dung pile, and (4) the grassland rodent Sigmodon hispidus harvests some of the germinating guanacaste seeds from the dung but leaves hard dormant seeds behind. These findings suggest that a guanacaste seed dispersal agent that defecates small numbers of seeds in many small piles of dung in grassland will be a better dispersal agent for guanacaste tree seeds than one that defecates many seeds in a few large dung piles in the nearby forest.