Abstract
Plants that are moved away from their parents are more likely to germinate and mature, and this is accomplished through either abiotic or biotic mechanisms. Biotic mechanisms involve animals as seed vectors, whereby animals displace seeds and deposit them unharmed in a new location. The directed dispersal hypothesis states that animals move seeds to nonrandom locations, which enhances the probability of germination and maturation. We used black walnut (Juglans nigra) seeds dispersed by eastern gray squirrels (Sciurus carolinensis) to test this hypothesis with respect to chemical composition of the soil at sites where seeds were deposited. We established nine stations at which we placed five mature walnut fruits (with their seeds). Each seed was attached to a sewing bobbin, and the loose end of the bobbin thread was tied to a fixed object. This method allowed us to track seeds removed by squirrels to where they were deposited. Chemical constituents of the soil were measured at the deposition site and a randomly-selected site to determine if squirrels moved seeds to nonrandom locations with respect to soil composition (an important determinant of germination success). We found no differences in chemical composition between deposition and random sites, and we conclude that squirrels do not select deposition sites based on chemical characteristics of the soil. This study does not, however, eliminate the possibility that squirrels select deposition sites based on other criteria, such as forest structure, and that such criteria may result in seed dispersal to nonrandom locations.
