Dispersal of sweet pignut hickory in a year of low fruit production, and the influence of predation by a curculionid beetle

Abstract

The rate at which fallen hickory nuts are removed from beneath the parent tree, and the effect on this rate of the seed predator Conotrachelus affinis , was studied in an oak-hickory forest in southeastern Michigan, USA, during a year in which few nuts were produced. The trees responded to Conotrachelus , which destroyed half the nut crop, by aborting inviable nuts during the summer. The seed dispersers, mostly gray squirrels, removed fallen nuts rapidly, showing the ability to distinguish viable nuts and remove them preferentially. The number of nuts removed in a week varies directly with the number available, and removal rate increases when many viable nuts are falling. The death of most seeds before dispersal, and the squirrels' efficiency at foraging on nuts and recovering them after burial, imply that successful hickory reproduction takes place only in years of heavy nut production.