Effect of Diet and Water Availability on Rattus norvegicus (Rodentia: Muridae) Distribution

Abstract

The distribution of the Norway rat Rattus norvegicus extends from the subarctic to the subtropics in Japan; yet it is limited by several factors. I discuss appropriate diet, water balance, and temperature as limiting factors based on surveys in the subarctic zone (Yururi-Moyururi, uninhabited islands in Hokkaido), the temperate zone (a business district in Yokohama and an uninhabited islet, Kaiho-2 in Tokyo Bay), and the subtropics (the Hahajima Islands in the Ogasawara Archipelago) in Japan. In Yururi-Moyururi, the rats recruited new generations in their population not only in the summer but also under snow cover, probably by preying on carcasses of their own species. In Yokohama, peaks of recruitment of their new generations were found in the winter and the summer, though the season with peaks changed every year. In Kaiho-2, rats stopped recruiting in the winter because of dehydration, and over the winter the group lost body mass as a result of body fat consumption. In Hahajima, rats lost body mass and preyed mainly on plant matter because of chronic dehydration. I conclude that protein-rich diets and water balance, but not temperature, are basic factors in the distribution of the Norway rat.