The Method to Make the List Based on the New Red List Categories by the Use of the Distribution Data Recorded at Random : A Case in the Butterflies in Nagano Prefecture

Abstract

For the purpose of searching the species to be listed in the Red Data List, all of 149 butterfly species living in Nagano Prefecture were examined by quantitative analysis based on the new Red List Categories (The Environment Agency, 1997). The distribution data of each species recorded at random from municipality units in 1980 to 1997 were used for the comparison with the older ones. As a result, it may be said that the decreasing ratio in the population of a certain species must be calculated considering the overlooking ratio, since we can not find out it from all the habitats. The overlooking ratio is calculated by the average of the apparent decreasing ratio in the populations of the increasing species in this case. It was 18.35% in the grassland species and 22.38% in the forest ones. It is also considered that in general, the overlooking ratio in the forest species is higher than that in the grassland species. Therefore, it is necessary to calculate the overlooking ratio on each of grassland or forest species by the average mentioned above or the regression analysis of the first degree between the apparent decreasing ratio in the population and the ratio of the number of the recent data to the older ones on the increasing species. In the species having strong migration ability or being less studied, the qualitative analysis should be added for the choice of the species satisfying the criteria for the Red Data List based on the distribution data recorded at random.