Lesson56 Balance of Nature
All the different plants and animals in a natural world are in a state ofbalance. This balance is achieved by the plants and animals interacting witheach other and with their non-living surroundings. An example of a naturalcommunity is woodland, which is usually dominated by a particular species ofplant, such as the oak tree in an oak wood. The oak tree in this example istherefore called the dominant species but there are also many other types ofplants, such as bushes, small trees, mosses, lichens and algae.
The plants of a community use carbon dioxide, oxygen, water and nitrogento build up their tissues using energy in the form of sunlight. The planttissues form food for the plant-eating animals which are in turn eaten bythe flesh-eating animals. Thus plants produce the basic food supply for allthe animals of a community. The animals themselves are the consumers, andare either herbivores or carnivores.
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, andfoxes. Some carnivores feed on herbivores, some feed on the smallercarnivores, while some feed on both. These food relationships between thedifferent 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 theherbivores that eat the plants and the carnivores that feed on theherbivores.
oak [植]橡树，橡木
moss 苔，藓
lichen [植]青苔，地衣，苔藓
algae 藻类，海藻
nitrogen [化]氮
carnivore 食肉动物
herbivore 草食动物
自然平衡
自然界所有不同的植物和动物都处于平衡状态。这种平衡是通过植物和动物互相作用，以及它们与非生命环境互相影响取得的。例如，林地是一个自然生物群落，它通常由一特定种类的植物所主导，比方说橡树林里的橡树。此例中的橡树因而被称为优势物种，但也有许多其他种类的植物，像灌木、小树、苔藓、地衣和藻类。
植物群落利用二氧化碳、氧气、水和氮生成能吸取阳光能量的组织。植物组织成为食草动物的食物，食肉动物又以食草动物为食。这样植物为生物群落里的所有动物提供了基本的食物。动物自身是取食者，或为食草动物，或为食肉动物。
举例来说，林地生物群落里的草食动物有兔子、鹿、老鼠，蜗牛以及昆虫，它们不时被食肉动物吃掉。林地里的食肉动物有大有小，从昆虫到猫头鹰和狐狸这样的动物。有些食肉动物捕食食草动物，有些吃更小的食肉动物，还有一些两种都吃。生物群落里不同物种间的食物关系称为食物链或食物网。所有的食物链均开始于植物。食物链的链环是以植物为生的食草动物和捕食食草动物的食肉动物。 |