Protein-rich diet and water balance as limiting factors in the geographical distribution of the Norway rat, <i>Rattus norvegicus</i>

Abstract

The distribution of the Norway rat, Rattus norvegicus, extends from the subarctic and subantarctic zones to the tropics yet is limited by several factors. I discuss the 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), the subtropics (the Hahajima Islands in the Ogasawara Archipelago), and the tropics (Bangkok and Chanthaburi, Thailand). In Yururi-Moyururi, the rats recruited in the group under snow cover and in the summer. In Yokohama, the recruitment peeks fluctuated from year to year. In Kaiho-2, rats stopped recruiting in the winter because of dehydration, and the overwintered 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. In cities in Thailand, rats likely thrived by preying on food sources in water systems. I conclude that protein-rich diets and water balance are basic factors in the distribution of the Norway rat, as shown in the results for Kaiho-2 and Hahajima.