Seed predation and defleshing in the agouti-dispersed palmAstrocaryum standleyanum

Abstract

Abstract:The agouti (Dasyprocta punctata) meticulously defleshes Astrocaryum standleyanum palm seeds before scatter hoarding. On Barro Colorado Island, Panama, we experimentally tested three hypotheses on how this behaviour could reduce seed predation to the mutual benefit of the tree and the rodent. The first and established hypothesisthat defleshing reduces seed predation by bruchid beetles by intercepting larvae -was rejected. Experiments in which manually defleshed seeds or entire fruits were incubated at different times showed that defleshing reduced bruchid infestation before fruit fall but not after fruit fall. The second hypothesis -that defleshing reduces cache pilferage by making seeds less conspicuous -was supported. An experiment in which intact fruits and manually defleshed seeds were placed in mimicked agouti caches and followed showed that seeds with flesh were pilfered at higher rates than defleshed seeds. The third hypothesis -that defleshing reduces post-dispersal infestation of cached seeds -was rejected. An experiment in which intact fruits and manually defleshed seeds were placed in mammal exclosures and later collected to assess infestation showed that burial reduced seed infestation but defleshing did not. Thus, seed defleshing reduced palm seed predation, but in a different way than previously believed. We also found that (1) bruchid beetles can be pre-dispersal rather than post-dispersal seed predators, (2) seed infestation by scolytid beetles may control bruchid larvae, and (3) scolytids rather than bruchids are the main invertebrate seed predators of this palm.

Thieving rodents as substitute dispersers of megafaunal seeds

“…We tracked seeds of A. standleyanum, a large-fruited and large-seeded palm that is presumed to be adapted for seed dispersal by megafauna now extinct (1,2). A. standleyaum trees produce 10-g stony endocarps with large seeds, enclosed in brightorange, sweet-fleshy fruits (53). Astrocaryum on BCI has a seasonal fruiting peak during May-June, when each tree produces up to 1,500 fruits.…”

Evidence for cache surveillance by a scatter-hoarding rodent

“…Agoutis are 2e4 kg caviomorph rodents that scatter-hoard seeds as food reserves for periods of food scarcity (Smythe 1978(Smythe , 1989Jansen et al 2010). Agouti home ranges on the island average 2.71 ha and overlap widely with the home ranges of other agoutis (Emsens et al 2013).…”

Defaunation affects Astrocaryum gratum (Arecales: Arecaceae) seed survivorship in a sub-montane tropical forest

“…By setting treatments far from parental trees and in low densities, the experimental design may have reduced the impacts of insect infestation. Conversely, higher insect predation was detected in the hunted forest than in the other forest types, because there are more rodents (squirrels) and fewer agoutis which depredate insect-infected seeds (Silvius, 2002;Jansen et al, 2010). The low overall insect infection rate may have been reduced by set plots in areas with low seed densities as presentd by Cintra (1997).…”

“…The seeds were then placed in the treatment exclosures (Jansen et al, 2010). The area around each block was cleared (up to 10m) of any possible A. gratum seeds until no seeds were found, to easily locate and recover tested seeds that may had been moved and deposited nearby.…”

“…or agoutis (Dasyprocta spp.) are attracted to fruits on the forest floor and they then move seeds longer distances, sometimes engaging in scatter-hoarding or seed caching behaviors (Jansen, Elschot, Verkerk, & Wright, 2010). When dispersed long distances, seeds had higher survivorship with lower interspecific competition and invertebrate infestation; e.g., Coleoptera; Bruchids, Scolytine.…”