Probable relation of increase in big buildings and road coverage to the rise and decline of Rattus rattus in Sapporo, Japan

Abstract

Major cities such as Sapporo, Sendai, Shinjuku, Yokohama, and Nagoya, Japan, have experienced Rattus rattus infestations since the 1970s. The problem has disappeared in the 1980s in Sapporo where the R. rattus populations have decreased. The causes of the rise and decline were analyzed with aerial photographs of commercial districts in the five cities. In each city, the total basal area of buildings>10m high increased from 5-10% in the mid-1960s to>15% in the 1970s. In 1988-1990,the mean road coverage per hectare for Sapporo was 0.424±0.133ha, which was significantly larger at the 5% level than 0.334±0.156ha, 0.374±0.195ha, 0.351±0.136ha, and 0.374±0.169ha for Sendai, Shinjuku, Yokohama, and Nagoya, respectively. The coefficient of variation of 31.4% for Sapporo was apparently smaller than that for the other cities. Road coverage in Sapporo is generally large, but those in the other cities vary in size which explains Sapporo's low value. The rapid increase of big buildings in the 1970s may have expanded the infestations in most cities. In Sapporo, however, the large road coverage may have fragmented habitats of the rats and it is possible that rat populations declined as a result.