Pulp handling by vertebrate seed dispersers increases palm seed predation by bruchid beetles in the northern Amazon

Abstract

1The simultaneous use of fruits and seeds by invertebrate seed predators and vertebrate seed dispersers produces complex ecological interactions that reduce the predictability of seed fate. 2 Cocosoid palm seeds in the Neotropics are subject to high mortality by bruchid beetle infestation and such attack is the major cause of mortality for seeds of the palm Attalea maripa at our study site in the northern Brazilian Amazon. 3 The exocarp and mesocarp of 1400 fruits were manipulated in different ways to simulate handling by vertebrates. No eggs of the bruchid beetle, Pachymerus cardo , were laid on intact control fruits, while the highest numbers of eggs were received by fruits whose exocarp and mesocarp had been partially removed, as if by primates and rodents (mean of 15.9 and 18.9 eggs fruit − 1 , respectively, during the peak fruiting season). Fruits with intact mesocarp but no exocarp, and fruits with all mesocarp and exocarp removed, received low numbers of eggs (mean of 4.6 and 6.6 eggs per fruit, respectively, during the peak fruiting season). Thus both exocarp and mesocarp deter oviposition, and removal of these fruit structures increases fruit susceptibility to infestation. 4 Oviposition rates declined as the fruiting season progressed, but oviposition preferences remained the same. Seed mortality was high for any fruit on which eggs were laid. 5 Large rodents and primates, which have been considered among the most effective seed dispersers for large-seeded Neotropical trees such as palms, actually increased the susceptibility of seeds to bruchid beetle attack. Removal of (intact) seeds by other dispersers may be necessary to ensure seed survival. 6 These results indicate that the reliability of seed dispersers cannot be gauged without a complete understanding of variables that affect seed viability.

Seed predation and defleshing in the agouti-dispersed palmAstrocaryum standleyanum

“…All palm bruchids (subfamily Pachymerinae) were believed to be in guild C, infesting endocarps only after fruit have fallen to the ground (Johnson & Romero 2004). Removal of the exocarp and mesocarp facilitates subsequent oviposition and enhances seed predation by guild C species, for example in Speciomerus giganteus attacking Attalea butyracea in Costa Rica and Panama (Janzen 1971b, Wright 1983, in P. cardo attacking A. maripa in Brazil (Silvius & Fragoso 2002), and in Caryoborus serripes attacking Astrocaryum chambira in Peru (Delgado et al 1997). Exocarps protect seeds against guild C species, and fruit handling by mammals gives bruchid beetles access to the endocarps (Silvius 2005).…”

Do fruit morphology and scarification affect germination and predation rates of Babassu seeds?

“…As such, it is possible that there is, in fact, seasonal variation in predation as was reported by Silvius & Fragoso (2002), who observed the predation rate of P. cardo on A. maripa to vary from 60 to 94 %, during the dry and rainy seasons, respectively. Attalea phalerata fruits exposed for eight months, including the rainy season, demonstrated 60 % predation by P. cardo (Castro & Roldan 2001), although A. arenaria, which also demonstrated continuous fruiting, suffered 20.6 % predation by P. nucleurum (Grenha et al 2008).…”

“…Acrocomia aculleata, A. speciosa, and Syagrus oleracea, which grow up to 10 m in height, likewise demonstrated seed predation by P. nucleurum (a congeneric species) only in the post-dispersal phase (Garcia et al 1980;Scariot 1998). However, Silvius & Fragoso (2002) and Grenha et al (2008) reported seed predation in the shorter palms (approximately 2 m tall) Bactris acanthocarpa and Allagoptera arenaria (Arecaceae) (Dasyprocta spp. ; Dasyproctidae) (Guix 2006).…”

“…; Dasyproctidae) (Guix 2006). Silvius & Fragoso (2002) reported that the predation of A. maripa seeds by P. cardo was more severe when the fruit epicarps and mesocarps had been partially removed. Janzen (1971) noted that the seed beetle, probably Speciomerus giganteus, would not oviposit on A. butyracea if the fruitpulp had not been previously moved by vertebrates or fungal growth.…”

“…Of those 30 fruits from each palm, 15 were scarified using the methodology described above to the depth of the endocarp on the extremity of the fruit (where the petiole would emerge) and 15 were maintained intact as controls. This manual scarification of the fruits was performed to simulate natural scarification by rodents, as described by Silvius & Fragoso (2002) for A. maripa (Aubl.) Mart., and the scarification of A. vitrivir fruits by invertebrates (personal observations).…”