Effect of seed caching by Parus varius on germination in Styrax japonica

Abstract

We examined the seed dispersal and germination of Styrax japonica to determine the effects of the fruit pulp involving saponin and its removal by the varied tit (Parus varius) on the seed germination in a broad-leaved forest of northern Japan. All mature fruits disappeared from the trees by September. Only varied tits visited the trees, and 80% of their visits were spent on transporting mature fruits in four days. As 83.0 to 87.2% of the fruit that disappeared from trees was taken by varied tits, most of the fruit was probably transported from the trees by these birds. The remaining fruits naturally fell to the ground, and their pulp remained until mid November. In a germination experiment in the field, the seeds deliberately extracted from the fruit pulp had a significantly higher rate of germination (mean 36%) than the intact fruits (mean 4%). Since the level of saponin in the fruit pulp decreased after the fruit fell to the ground, it is unlikely that saponin in the fruit pulp prevents seed germination. The caching behavior of varied tits probably contributes not only to seed dispersal but also to seed germination because it accompanies the extraction of fruit pulp, which prevents seed germination.