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

Abstract

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 3 yrs 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 3 yrs, 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, frugivore–granivore abundances, and seed‐handling capabilities. Mammal–seed interactions are complex; the outcomes of these interactions depend on the inherent characteristics of seeds and their potential dispersers.

Monitoring the Status and Trends of Tropical Forest Terrestrial Vertebrate Communities from Camera Trap Data: A Tool for Conservation

“…However, as discussed above, agoutis and pacas may be competing with each other and with peccaries [40]. If competition with peccaries alone is driving these declines, we expect that occupancy of pacas and agoutis will remain low, while peccary occupancy will remain high or increase.…”

“…There is some evidence of seed competition between peccaries and agoutis at La Selva [40], with agoutis being less efficient at removing seeds than peccaries. Pacas feed on soft fruits rather than seeds, so they are unlikely to compete with agoutis, but likely competing with peccaries who are also fruit eaters.…”

The omnivorous collared peccary negates an insectivore-generated trophic cascade in Costa Rican wet tropical forest understorey

“…If the predation risk imposed by abundant insectivorous herpetofauna within the bird/bat exclosures exceeded the predation risk outside the exclosures, leaf damage would be reduced within the netted exclosures -as we observed. Thus the peccaries, which are highly abundant at La Selva (Kuprewicz 2013) and have relatively small home ranges (38-305 ha in tropical forest; Keuroghlian et al 2004), may have repeatedly herded vulnerable small herpetofauna inside our netted exclosures, initiating a trait-mediated trophic cascade that reduced Diptera density and leaf damage. Further studies are needed to investigate herpetofauna densities within and outside bird/bat exclosures with and without peccaries.…”

Small traits with big consequences: how seed traits of nitrogen‐fixing plants might influence ecosystem nutrient cycling

“…Nitrogen (N) is a commonly limiting nutrient to primary production in terrestrial ecosystems worldwide (LeBauer and Treseder , Thomas et al ). Symbioses between N‐fixing bacteria and certain higher plants (hereafter we refer to the plants as ‘N fixers’) represent the largest potential natural input of N into ecosystems through their conversion of atmospheric di‐nitrogen gas (N 2 ) into bio‐available forms of N (Sprent ).…”

“…Seed characteristics such as seed size, shape, color, appendages, sugar and nutrient content, and the presence of secondary compounds determine the primary dispersal vector(s) of a seed and how effectively seeds disperse to environments that are conducive to germination (Howe and Smallwood , Cipollini and Levey , Schupp and Jordano , Howe ). For example, species with heavy seeds that are primarily dispersed by terrestrial animals can have different distribution patterns than species with light seeds that are primarily wind dispersed (Moles et al , Eriksson , Thomson et al 2011, Galetti et al ). Thus, seed traits that are common for N fixers may influence the dispersal vectors, distribution patterns in time and space, and ultimately the biogeochemical roles of these plants in an ecosystem.…”