Are seeds of trees with higher fruit production dispersed farther by frugivorous mammals?

Abstract

ABSTRACT Previous studies have estimated distributions of seed dispersal distance by a variety of methods. But apart from direct observation, these methods cannot clarify the absolute numbers of seeds dispersed by each disperser. Without the ability to calculate absolute spreading volumes, each dispersers’ contribution cannot be quantitatively evaluated. To resolve this problem, we estimated and compared quantities and distances of seed dispersal by mammalian seed dispersers. We focused on the fruits of Cerasus leveilleana and five species of frugivorous mammals that forage on it, central Japan. We tracked wild individuals of each species and gut retention times of seeds in captive individuals. By observing wild C. leveilleana trees for 2 years, we calculated fruit production, visitation frequency, and numbers of fruits removed per visit by each species. The mammal species differed greatly in body size and foraging behavior, and thus in the seed dispersal patterns that they generated: not only in dispersal distance, especially long distance, but also in the number of seeds removed. In particular, total seed removal and long-distance dispersal tended to be greater when fruit production was greater, and they were strongly affected by occasional visitation by bears. Therefore, understanding the relative functional importance of seed dispersers requires direct comparison of their effectiveness at seed dispersal. Large differences in the seed disperser fauna between years due to interannual variation in fruit production suggest that observations of many trees with different amounts of fruit production over multiple years are needed to clarify how fruiting trees and seed dispersers interact.