Island biogeography of the Japanese terrestrial mammal assemblages: an example of a relict fauna

Aim The aim of this paper is to provide a review of the biogeography of the terrestrial mammalian fauna from the Japanese islands. Location The Japanese archipelago is located off the eastern coast of Asia. It extends over a distance of approximately 2000 km in length, from north to south, and comprises more than 3900 islands of widely differing areas. Methods The list of the living and Quaternary mammalian fauna of Japan and its geographical distribution as compiled ffrom various published works. Introduced species, marine mammals and bats were not considered in this study. Simpson and Jaccard indices were used to quantify the similarities between the fauna from twelve selected islands from the Japanese archipelago. Regression lines and Pearson correlation coefficients were used to describe the relations between species richness and various geographical factors of the islands, such as area or descriptors of isolation. Lastly, we used the method proposed by Atmar & Patterson (1993) to measure the degree of nestedness of the Japanese terrestrial mammalian fauna. Results Species richness on islands is highly correlated with island size. However, this study reveals the importance of non-equilibrium effects. At a large scale, the current distribution of mammals in Japan seems to be due to selective post-glacial extinction processes. A large proportion of the Japanese mammals are endemic forms, and extinctions were not balanced by the colonization of species from the Asiatic mainland. In addition, we show the major role played by inter-island dispersal processes, in particular from larger islands towards smaller ones, that are mainly effected by the presence of deep marine channels between islands. Main conclusions The present distribution of the terrestrial mammalian fauna from Japan is thus mainly the result of post-glacial extinctions that were not compensated for by colonization of new species from the faunal Asiatic mainland source pool. However, this study emphasizes the importance of inter-island dispersal processes.