第三冊第3篇：自然平衡

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All the different plants and animals in a natural world are in a state of balance. This balance is achieved by the plants and animals interacting with each other and with their non-living surroundings. An example of a natural community is woodland, which is usually dominated by a particular species of plant, such as the oak tree in an oak wood. The oak tree in this example is therefore called the dominant species but there are also many other types of plants, such as bushes, small trees, mosses, lichens and algae.

自然界所有不同的植物和動物都處于平衡狀態(tài)。這種平衡是通過植物和動物互相作用，以及它們與非生命環(huán)境互相影響取得的。例如，林地是一個自然生物群落，它通常由一特定種類的植物所主導，比方說橡樹林里的橡樹。此例中的橡樹因而被稱為優(yōu)勢物種，但也有許多其他種類的植物，像灌木、小樹、苔蘚、地衣和藻類。

The plants of a community use carbon dioxide, oxygen, water and nitrogen to build up their tissues using energy in the form of sunlight. The plant tissues form food for the plant-eating animals which are in turn eaten by the flesh-eating animals. Thus plants produce the basic food supply for all the animals of a community. The animals themselves are the consumers, and are either herbivores or carnivores.

植物群落利用二氧化碳、氧氣、水和氮生成能吸取陽光能量的組織。植物組織成為食草動物的食物，食肉動物又以食草動物為食。這樣植物為生物群落里的所有動物提供了基本的食物。動物自身是取食者，或為食草動物，或為食肉動物。

Examples of herbivores in a woodland community are rabbits, deer, mice, snails, and insects. The herbivores are sometimes eaten by the carnivores. Woodland carnivores are of all sizes, from insects to animals like owls, and foxes. Some carnivores feed on herbivores, some feed on the smaller carnivores, while some feed on both. These food relationships between the different members of the community are known as food chains or food webs. All food chains start with plants. The links of the chain are formed by the herbivores that eat the plants and the carnivores that feed on the herbivores.

舉例來說，林地生物群落里的草食動物有兔子、鹿、老鼠，蝸牛以及昆蟲，它們不時被食肉動物吃掉。林地里的食肉動物有大有小，從昆蟲到貓頭鷹和狐貍這樣的動物。有些食肉動物捕食食草動物，有些吃更小的食肉動物，還有一些兩種都吃。生物群落里不同物種間的食物關系稱為食物鏈或食物網。所有的食物鏈均開始于植物。食物鏈的鏈環(huán)是以植物為生的食草動物和捕食食草動物的食肉動物。