Fruit removal rates from aggregated and isolated bushes of the red elderberry, Sambucus pubens

Abstract

In July in northern Wisconsin, the red elderberry (Sambucus pubens (Michx.) synchronously ripens large panicles of bright red, small, watery, sweet drupes. During 1982 and 1983, I monitored bushes aggregated along an old logging track or isolated in tree-fall clearings to investigate the effects of isolation, crop size, and fruit quality on fruit removal by birds. All three factors significantly affected rates of fruit removal, although fruit removal rates were primarily a function of crop size. More fruits per bush per day were removed from large crops of both aggregated and isolated plants. Fruits were not removed disproportionately faster from plants with large than with small crops in either habitat. These results do not support the hypothesis that differential probability of dispersal success is an important selective factor in the evolution of delayed first reproduction or supraannual fruiting periodicities. However, removal rates from aggregated plants were lower than from isolated bushes in tree-fall clearings, probably an effect of local competition for frugivores. Sugar content of the pulp (but not fruit size) also significantly affected rates of fruit removal.