テンの食性分析における頻度法とポイント枠法の比較

Abstract

テン（ホンドテンMartes melampus melampus）の糞分析において頻度法とポイント枠法との関係を確認するために，289個の糞試料にもとづき，以下の検討をした．頻度法による12の食物カテゴリーの頻度％（頻度百分率）とポイント枠法によって得られた占有率の関係をみると，頻度％，占有率ともに大きい果実と，頻度％が60～70％で占有率が10％前後の昆虫，種子，茎・葉の3カテゴリーと，頻度％，占有率とも小さいその他の8カテゴリーに3分された．主要5カテゴリーをみると，種子，茎・葉，哺乳類は頻度％（x）－占有率（y）に相関があり，その勾配（y＝axの定数a）は前2者では0.2未満であったのに対して，哺乳類では0.4と大きかった．果実と昆虫では頻度％と占有率に相関がなかった．これは果実と昆虫は供給量の季節変化が大きいためと考えた．以上より，テンの糞分析では頻度評価からおおまかに占有率評価を読み取ることができるが，昆虫，種子，茎・葉では過大評価になることに留意すべきであると結論した．Since the frequency method for animal food habits over-estimates or under-estimates food compositions, it is necessary to find the relationship between frequency evaluation and occupation evaluation. This analysis adopted the point-frame method for the Japanese marten Martes melampus. The results of both methods were compared against 289 fecal samples. Among the 12 food categories, fruits showed the greatest values for both frequency and occupancy, followed by insects, seeds, and stems-leaves, and others showed small frequency and occupancy values. The occupancies of insects, seeds, and stems-leaves were apparently smaller than the frequency values. The occupancy values (x) of seeds, stems-leaves, and mammals positively correlated with frequency values. The coefficients a in y = ax equation were < 0.2 for the former two, but around 0.4 for mammals. Occupancy values for fruits and insects did not correlate with frequency values because of great seasonal variations in availability. Accordingly, it seems possible to read frequency values of martens’ foods as far as we were cautious of overestimation in insects, seeds, and stems-leaves.