物種數量（豐富度）下降有害于生態(tài)系統(tǒng),，而保護工作則基本上以保護或恢復特定稀有物種為重點。然而,，物種相對風度（均勻度）之間更大的差別也可能對生態(tài)有害,，而這種狀況只能通過同時改變很多物種的密度來逆轉。
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對以傳統(tǒng)方式管理的有機土豆地所做的一項新的調查表明,，物種均勻度在有機管理方式下更大,。在一項田間試驗中，研究人員對這些層次的均勻度進行復制，其結果表明,，有機地里所發(fā)現的天敵的均勻度可以促進害蟲控制和增加作物生物質,。在有機作物中，很多有益物種（吃害蟲的物種）同樣普遍,，對土豆來說這樣會導致害蟲更少,、植株更大。(生物谷Bioon.net)
生物谷推薦原文出處：
Nature doi:10.1038/nature09183
Organic agriculture promotes evenness and natural pest control
David W. Crowder,Tobin D. Northfield,Michael R. Strand& William E. Snyder
Human activity can degrade ecosystem function by reducing species number (richness)1, 2, 3, 4 and by skewing the relative abundance of species (evenness)5, 6, 7. Conservation efforts often focus on restoring or maintaining species number8, 9, reflecting the well-known impacts of richness on many ecological processes1, 2, 3, 4. In contrast, the ecological effects of disrupted evenness have received far less attention7, and developing strategies for restoring evenness remains a conceptual challenge7. In farmlands, agricultural pest-management practices often lead to altered food web structure and communities dominated by a few common species, which together contribute to pest outbreaks6, 7, 10, 11. Here we show that organic farming methods mitigate this ecological damage by promoting evenness among natural enemies. In field enclosures, very even communities of predator and pathogen biological control agents, typical of organic farms, exerted the strongest pest control and yielded the largest plants. In contrast, pest densities were high and plant biomass was low when enemy evenness was disrupted, as is typical under conventional management. Our results were independent of the numerically dominant predator or pathogen species, and so resulted from evenness itself. Moreover, evenness effects among natural enemy groups were independent and complementary. Our results strengthen the argument that rejuvenation of ecosystem function requires restoration of species evenness, rather than just richness. Organic farming potentially offers a means of returning functional evenness to ecosystems.
