Ecological comparison and Molecular Phylogeny of Japanese Pygmy Woodpecker Populations

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One of the ways to understand the origin of the avian community, is to explore the history of establishment of the local populations of each species. Species-distance rule, an important biogeographic rule as well as that of species-area, usually says more species or higher colonization rate on the closer island to the source. However, there are several islands without the Japanese Pygmy Woodpecker (JPW, Picoides kizuki) close to Japanese Main islands, in spite of that there is good enough forest habitat. JPW is a common species in Japanese archipelago and in a wide variety of forests, including small forest islands around the cities. This fact suggests there are some factors which limit a species colonization on the closer habitat island. Predators can be one of them, but not for JPW, because the species expanded its distribution in 1980's into urban area, where the number of predators such as Jungle Crow and Brown-eared Bulbul also increased their population there at that time. The forest had been fragmented and isolated in this era. I think the longer distance might made JPW to colonize at the city parks or short time extinction rate is lower on the distant forest islands. The same mechanism could have been worked in the geographic situation of JPW. I have been reconfirming the distribution pattern of JPW and compared the wing shape of several JPW populations. The wing was pointed less on Okinawa and Amami Islands, southern and remote islands, suggesting their lower flight ability. However it was sharper on Miyake island of middle distance than it was in the source mainland. There are several JPW lacking islands between main land and those islands. These facts seem to support the hypothesis.