Predation and dispersal of large and small seeds of a tropical palm

Seed size may vary greatly among individuals within plant species. What eff ects the extremes of this variation have for seeds taken by small mammals a re poorly understood. Not all seeds removed by small mammals are necessaril y eaten. Small rodents are common seed predators, but they may disperse a s ignificant proportion of seeds by scatter hoarding them via burial. Size-de pendent predation and dispersal of seeds has not been directly tested withi n a plant species for tropical rodents. This study tested whether or not la rge and small nuts of Astrocaryum mexicanum (Palmae) differed in their fate s due to handling by the spiny pocket mouse Heteromys desmarestianus (Heter omyidae). Exclosures were used to give small rodents exclusive access to A. mexicanum nuts. H. desmarestianus preferentially consumed large over small A. mexicanum nuts, but cached (in burrows and by scatter hoarding) similar proportions of these nuts by size. Small nuts tended to be buried farther away from exclosures than large nuts. Although sample sizes of buried nuts were Small, the rodents retrieved all buried large nuts, but 30% of the sma ll nuts remained buried long enough to germinate. I also examined predisper sal predation by insects and found that insects appear to have no size pref erence for A. mexicanum nuts, but insect predation appears to hinder nut de velopment. Thus, nuts attacked by insects develop to be significantly small er, with a low proportion of undamaged endosperm, than uninfested nuts. It is hypothesized that the preferential predation of large A. mexicanum nuts by H. desmarestianus is a response by these rodents to insect predation.