安定同位体比を用いた河川食物網研究：エンドメンバーの変動は何によって決まるのか？

石川　尚人

食物網研究において炭素・窒素安定同位体比（δ¹³C、δ¹⁵N）は、生物の餌起源と栄養段階を推定できることから幅広く利用されている。特に河川生態系においては、生物は岩石に付着している藻類（付着藻類）を主とする内部生産産物と陸上植物リターを主とする外部生産産物という2つの炭素起源に依存している。このうち付着藻類のδ¹³Cは光合成における同位体効果により同一河川内で変動を示すが、リターのδ¹³Cはほぼ一定の値を示すことが知られている。一方、δ¹⁵Nは河川集水域の土地利用形態や栄養環境によって、河川間で異なることが予測されると共に、一般に集水域面積の増加に伴い上昇することが知られている。本発表ではδ¹³C、δ¹⁵Nを用いた河川食物網研究のレビューと共に、特に付着藻類のδ¹³C，δ¹⁵Nについて既存の各研究からデータを取り出し、メタ解析アプローチからこれらの変動要因を探る。そして最後に、δ¹³C、δ¹⁵Nによる食物網研究の利点と欠点、今後の展開に関して議論したい。

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