Nature2014-06-26 3:36 PM

植物的天敌促进生物多样性 Pathogens and insect herbivores drive rainforest plant diversity and composition

论文摘要 

热带雨林异常高的物种丰富度需要一些解释,而令人信服的一个解释,即Janzen–Connell效应,听起来违反直觉。它认为,群落多样性受到真菌病原体和地面上的食草昆虫等天敌的促进,这些天敌使得任何“寄种”个体都不能变的太普遍。这篇论文报告了在伯利兹的“Chiquibul森林保护区”所做实验。在实验中,真菌和昆虫在受控条件下被从林地中清除。结果证实,真菌病原体能促进高植物多样性,食草昆虫改变这些植物群落的组成。

Abstract 

Tropical forests are important reservoirs of biodiversity, but the processes that maintain this diversity remain poorly understood. The Janzen–Connell hypothesis suggests that specialized natural enemies such as insect herbivores and fungal pathogens maintain high diversity by elevating mortality when plant species occur at high density (negative density dependence; NDD). NDD has been detected widely in tropical forests, but the prediction that NDD caused by insects and pathogens has a community-wide role in maintaining tropical plant diversity remains untested. We show experimentally that changes in plant diversity and species composition are caused by fungal pathogens and insect herbivores. Effective plant species richness increased across the seed-to-seedling transition, corresponding to large changes in species composition5. Treating seeds and young seedlings with fungicides significantly reduced the diversity of the seedling assemblage, consistent with the Janzen–Connell hypothesis. Although suppressing insect herbivores using insecticides did not alter species diversity, it greatly increased seedling recruitment and caused a marked shift in seedling species composition. Overall, seedling recruitment was significantly reduced at high conspecific seed densities and this NDD was greatest for the species that were most abundant as seeds. Suppressing fungi reduced the negative effects of density on recruitment, confirming that the diversity-enhancing effect of fungi is mediated by NDD. Our study provides an overall test of the Janzen–Connell hypothesis and demonstrates the crucial role that insects and pathogens have both in structuring tropical plant communities and in maintaining their remarkable diversity.

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