Mammal Abundances and Seed Traits Control the Seed Dispersal and Predation Roles of Terrestrial Mammals in a Costa Rican Forest

摘要

In Neotropical forests, mammals act as seed dispersers and predators. To prevent seed predation and promote dispersal, seeds exhibit physical or chemical defenses. Collared peccaries (Pecari tajacu) cannot eat some hard seeds, but can digest chemically defended seeds. Central American agoutis (Dasyprocta punctata) gnaw through hard-walled seeds, but cannot consume chemically defended seeds. The objectives of this study were to determine relative peccary and agouti abundances within a lowland forest in Costa Rica and to assess how these two mammals affect the survival of large seeds that have no defenses (Iriartea deltoidea, Socratea exorrhiza), physical defenses (Astrocaryum alatum, Dipteryx panamensis), or chemical defenses (Mucuna holtonii) against seed predators. Mammal abundances were determined over 3yrs from open-access motion-detecting camera trap photos. Using semi-permeable mammal exclosures and thread-marked seeds, predation and dispersal by mammals for each seed species were quantified. Abundances of peccaries were up to six times higher than those of agoutis over 3yrs, but neither peccary nor agouti abundances differed across years. Seeds of A.alatum were predominantly dispersed by peccaries, which did not eat A.alatum seeds, whereas non-defended and chemically defended seeds suffered high levels of predation, mostly by peccaries. Agoutis did not eat M.holtonii seeds. Peccaries and agoutis did not differ in the distances they dispersed seeds. This study shows that seed fates are contingent upon many factors such as seed defenses, frugivoregranivore abundances, and seed-handling capabilities. Mammalseed interactions are complex; the outcomes of these interactions depend on the inherent characteristics of seeds and their potential dispersers.