Fruiting phenology of animal-dispersed plants in response to winter migration of frugivores in a warm temperate forest on Yakushima Island, Japan

Abstract

The fruiting phenology of animal-dispersed plants was observed in a warm temperate, evergreen forest on Yakushima Island. The number of ripe fruits was counted for 22 trees, four lianas and one parasitic epiphyte species with sapfruit. These fruits were consumed by birds and Japanese macaques (Macaca fuscata yakui). Birds with small gapes (e.g. Japanese white-eye [Zosterops japonica]) consumed only small fruit less than 6 mm in diameter, while birds with large gapes (e.g. red-capped green pigeon [Sphenurus formosae]) and Japanese macaques consumed a wide range of fruits from 4 to 16 mm in diameter. The larger animals did not ignore the smaller fruits. Brown-eared bulbul (Hypsipetes amaurotis) and Japanese white-eye were the main consumers of sapfruit in terms of frequency in winter. Some of the observed consumers were year-round residents, but most of the consumers migrated to Yakushima Island from the main islands of Japan to overwinter (from November to March), and their abundance in winter was four times as high as during the rest of the year (from May to October). In 23 of the 27 plant species investigated, sapfruit production coincided with their immigration season, whereas tree species bear capsules and nuts during autumn from September to November. We suggest that sapfruit species set their ripe period to the season when frugivorous birds are most abundant.