The role of Japanese macaques (Macaca fuscata) as endozoochorous seed dispersers on Kinkazan Island, northern Japan

Yamato Tsuji, Kaede Sato, and Yoshikazu Sato

宮城県金華山島に生息する野生ニホンザルによる種子散布特性について調べました。1999年から2009年にかけて島内で収集した1294個の糞を分析し、 1)種子の出現率、2)出現する植物種の生活史タイプ、3)種子数、4)健全率をそれぞれ調べました。いずれの月の糞からも種子が出現しましたが、 その内容は月ごとに大きく異なり、夏と秋には種子の総数がもっとも多く、また健全率がもっとも高くなっていました。サルはこれらの季節に多様な植物の種子を広範囲に散布していると 考えられます。全期間を通じて、サルは22科35種の植物の種子を散布しており、その中には12種の草本種子も含まれていました。これまで、島内における草本類の散布はもっぱらニホンジカが行っていると 考えられてきましたが、本研究を通じて、サルも草本類の散布に貢献している可能性が示されました。種子の健全率は種子サイズと相関がありました。 いっぽう、サルの食性の地域差が種子散布特性に与える影響を調べるために、地域間比較を行いました。自然林（金華山と屋久島）に生息するサルは、 より人の手の入った森林（下北半島、鹿島）に生息するサルに比べて木本植物の種子をより多く散布していました。糞一個当たりの出現種数にも地域差があり、暖温帯の屋久島で最も多くなっていました。 われわれの研究は、サルによって散布される種子の構成は決して固定されたものでなく、それぞれの場所の植生に強く影響されていることを示しています。

Mammalian Biology 76: 525-533

We studied the characteristics of seeds within faeces, an important aspect of endozoochorous seed dispersal, in Japanese macaques Macaca fuscata inhabiting Kinkazan Island, northern Japan. We intermittently collected faecal samples from 1999 to 2009 (N= 1294) and examined the rate of seed occurrence,species/life-form composition, number of seeds, and their intact rate. Seeds were found within faecal samples during every month, but their characteristics changed monthly: the rate of seed occurrence and the number of plant species within faecal samples were greater in summer and fall, and the intact rate and number of intact seeds observed within single faecal samples were also higher during these seasons than spring and winter. These results suggest that Japanese macaques on Kinkazan act as seed dispersers in summer and fall and that they disperse intact seeds into wider areas within the forest through defecation. During the study period, we observed seeds from a total of 35 plant species from 22 families in our samples. In addition to those of woody plants, we also observed seeds from as many as 12 herbaceous plants, for which sympatric sika deer (Cervus nippon) have historically been considered the sole seed dispersal agents. The intact rate of seeds was significantly negatively correlated with the seeds' mean cubic diameter, and this relationship was strengthened for non-fleshy fruits. We also conducted regional comparisons of the characteristics of defecated seeds in order to address whether regional variations in the diet of the macaques affect their efficacy as seed dispersers, both in terms of quantity and quality. Macaques living in the natural habitats of Kinkazan and Yakushima dispersed more seeds of tall tree species than do macaques inhabiting the human-altered areas of in Shimokita and Kashima. The number of plant species represented within single faecal samples also varied geographically, being greater in Yakushima. This pattern likely resulted from Yakushima’s warm temperate climate, as the other three study sites occur in the cool temperate region. Our results suggest that the composition of seeds dispersed by Japanese macaques is not rigid, but is determined instead by the vegetation found in a given habitat.

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