Abstract
To understand the patterns of fruit-bird interactions and to identify species with significant roles that are irreplaceable in these interactions (key species), we classified plant types according to traits relating to frugivory by birds, and analyzed the relationships between plant types and frugivorous birds in a primary lucidophyllous forest in Japan. At the 4-ha study site, 111 plant species were bird-dispersed and 15 common bird species were frugivorous. The growth form of plant species was divided into overstory, understory, and liana. The phenological pattern of fruiting was divided into “summer”, “fall”, and “persistent” from the temporal pattern of the seed rain. Fruits were classified in terms of size, as small, a size widely eaten by birds, and large, a size that is difficult for small birds to eat. Seventeen types of plant were identified in the study site, which were classified according to growth form, phenological pattern, and fruit size. Of these fruits, 14 species were considered to be major species, that is species that are both abundant and important for certain birds, and a further 20 species were identified as complementary species, that is species that compensate for a low diversity or for a temporal lack of the major species. Of the birds, eight species were considered major dispersal agents. The patterns of relationship between fruits and birds overlapped in various ways. No strong relationship in which species of fruits and birds are dependent almost entirely on each other were found. An important species set composed of three key species (Eurya japonica, Cleyera japonica, and Cornus controversa) and a group of summer fruits provided continuous and familiar food for many bird species. The patterns of relationship suggest that conservation of the overall composition of fruit types improves the stability of food resources for birds and facilitates dispersal success for the plants themselves.
