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Biologists who study nature's food chain agree about the basic links in the chain: sunlight provides fuel for plants, plants are consumed by herbivores, and herbivores are eaten by carnivores. But researchers aren't sure about all the factors that control the chain.
研究自然食物鏈的生物學家一致認為食物鏈有一個基本的關聯：陽光為植物提供養料，植物被食草動物吃，食草動物被食肉動物吃。但研究人員并不確定控制食物鏈的所有因素。
Traditionally, they have thought that food-chain populations are regulated from the bottom up. According to this idea, the availability of plants as food determines the size of animal populations in an area. But a study of a food chain in Isle Royal National Park, an island in Lake Superior, has shown that food-chain control can work in both directions.
習慣上，他們認為食物鏈上的種群數量受到自下而上的控制。根據這種觀念，可食用植物的面積決定了這個區域動物種群的大小。但位于蘇必利爾湖上一個小島上的皇家公園對食物鏈進行了一項研究，結果顯示食物鏈的控制是雙向的。
In the island's food chain, balsam firs are eaten by moose, which, in turn, are eaten by wolves. When researchers tracked the effects of the moose and wolves on the balsam firs, they actually found that the number of wolves in the area affected the growth of the firs. During the study, researchers recorded the width of the tree rings of balsam firs. Each ring marked a year of the tree's growth.
在這個島上的食物鏈中，香脂冷杉被駝鹿吃，反過來，駝鹿又被狼吃。當研究人員追蹤駝鹿和狼對香脂冷杉的影響時發現，這片區域狼的數量實際上也會影響冷杉的生長。在研究過程中，研究人員記錄了冷杉的年輪的寬度。每個年輪代表冷杉樹一年生長了多少。
A narrow ring indicated that the tree's growth had been suppressed that year. The narrow rings appeared only after wolf populations decreased, allowing a greater number of moose to survive and eat more balsam firs. The researchers concluded that wolves play an important role in maintaining the complex and delicate balance of the island's food chain. This food chain appears to be regulated from the top as well as from the bottom.
狹窄的年輪表示那一年樹的生長受到抑制。但狹窄的年輪只出現在狼的數量減少之后。狼群數量減少使更多的駝鹿存活下來，它們會吃掉更多的冷杉樹葉。研究人員總結到，狼群在保持這個島上食物鏈的復雜性和微妙的生態平衡上扮演著重要的角色。因此食物鏈即受到來自底部的控制，也受到來自頂部的控制。
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