肉食動物のない森林の断片の生態学的溶解
1Center for Tropical Conservation, Duke University, Box 90381, Durham, NC 27708, USA. manu@duke.edu
まとめ
肉食動物は草食動物集団をコントロールし,過剰な放牧を防ぐ. 肉食動物のない島々では,草食動物密度の増加により,木の苗木の生存率が低下し,上から下への生態系規制が実証されました.
科学分野:
- エコロジー エコロジー エコロジー
- 生態系規制に関する規則
- トロフィックカスケード (Trophic Cascades) とは
背景:
- 陸上の生態系の規制については,上から下に (捕食者制御) 対下から上に (植物の防御) という論争がある.
- ベネズエラの水力発電所によって作られた捕食動物のない島は,ユニークな自然実験を提供しています.
研究 の 目的:
- 生態系規制の競合する理論 (トップダウン対ボトムアップ) をテストする.
- 捕食者の不在が草食動物集団と植生に与える影響を調査する.
主な方法:
- 小さな島 (0.25-0.9ヘクタール) を研究し,動物が限られており,脊椎動物の捕食者が欠けている.
- 島と大陸における歯類,ウーラー猿,イグアナ,葉切りアリの密度を比較した.
- 草食動物に感染した島々で,天冠樹の苗木と小木の密度を評価した.
主要な成果:
- 草食動物 (ネズミ,猿,イグアナ,アリ) の密度は,島では大陸よりも10~100倍高かった.
- キャンピングの木の植え付けとサプリングの密度は,島々で大幅に減少しました.
- 脊椎動物捕食者の欠如は,草食動物の人口の増加と,その後の植生の減少につながった.
結論:
- 発見は,地上生態系における上から下への調節理論を裏付けている.
- 捕食者の不在は,トロフィックカスケードを引き起こし,植物コミュニティに深刻な影響を及ぼします.
- 生態系の構造は,捕食者の存在と活動によって大きく影響を受けます.
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