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. In troduced species, marine mammals and bats were not considered in this study . Simpson and Jaccard indices were used to quantify the similarities betwee n the fauna from twelve selected islands from the Japanese archipelago. Reg ression lines and Pearson correlation coefficients were used to describe th e relations between species richness and various geographical factors of th e islands, such as area or descriptors of isolation. Lastly, we used the me thod proposed by Atmar & Patterson (1993) to measure the degree of nestedne ss 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 J apanese mammals are endemic forms, and extinctions were not balanced by the colonization of species from the Asiatic mainland. In addition, we show th e major role played by inter-island dispersal processes, in particular from larger islands towards smaller ones, that are mainly effected by the prese nce of deep marine channels between islands. Main conclusions The present distribution of the terrestrial mammalian faun a from Japan is thus mainly the result of post-glacial extinctions that wer e not compensated for by colonization of new species from the faunal Asiati c mainland source pool. However, this study emphasizes the importance of in ter-island dispersal processes.