Abstract
Fukue et al. (2011) compared some methods for food habit analyses of carnivores and concluded that the point-frame method contains many problems: 1) it is 2-dimensional and so is not suitable for 3-dimensional foods, 2) it requires correction factors to estimate food compositions, 3) it is suitable for ungulates’ food habits but not for carnivores, 4) it overlooks uncommon food items, and 5) it has not been often used and thus comparison with the former studies is difficult. This evaluation is, however, not correct. First, the weight method and the volume method express 3-dimensions and the point-frame method expresses 2-dimensions. These adopt different dimension and all are adequate. Second, all three methods contain the problem of bias of digestibility, but the correction is a different subject. Third, ungulates often ingest 3-dimensional foods like fruits while omnivorous carnivores like raccoon dogs or foxes ingest 2-dimensional foods like leaves, and thus it is not correct to conclude that the point-frame method is suitable only to ungulates. Fourth, overlooking small and low frequency materials is inevitable for all of these methods. Finally, the frequency of use of these methods used in the past is not very important, and the quality of methods should be considered. Although the frequency method can evaluate only occurrence, the weight method, the volume method, and the point-frame method (area method) can quantify occupancy as well as frequency. The point-frame method can save time and does not require special equipment, and is therefore advantageous for data accumulation from “citizen science”.
