📚 Food Chains and Food Webs | 食物链与食物网
In every ecosystem, living organisms depend on one another for food. A food chain shows a single path of energy transfer from one organism to another, while a food web connects many food chains to reveal how energy flows through a whole community. Understanding these ideas helps us explain why organisms live where they do and why changes to one species can affect many others.
在每个生态系统中，生物都彼此依赖获取食物。食物链显示能量从一个生物传递到另一个生物的单一路径，而食物网连接许多食物链，揭示能量如何在整个群落中流动。理解这些概念有助于解释生物为何生活在特定地点，以及一个物种的变化为何会影响许多其他物种。
1. What is a Food Chain? | 什么是食物链？
A food chain is a linear sequence that shows what eats what in an ecosystem. The arrow in a food chain always points from the organism being eaten to the organism that eats it, showing the direction of energy transfer.
食物链是显示生态系统中谁吃谁的线性顺序。食物链中的箭头总是指向被吃者到吃者，表示能量传递的方向。
ss is eaten by the rabbit, and the rabbit is eaten by the fox. The arrows show that energy stored in grass moves to the rabbit, then to the fox.
例如，一条简单的草原食物链是：草 → 兔 → 狐狸。草被兔吃，兔被狐狸吃。箭头表示储存在草中的能量转移到兔，再转移到狐狸。
Food chains usually have no more than four or five links because energy is lost at each step. This loss limits how long a chain can be.
食物链通常不超过四到五个环节，因为每一步都会损失能量。这种损失限制了食物链的长度。
2. Producers: The Start of Every Chain | 生产者：食物链的起点
Producers are organisms that make their own food using energy from sunlight. On land, most producers are green plants; in oceans and lakes, algae and phytoplankton are the main producers.
生产者是利用阳光能量自己制造食物的生物。在陆地上，大多数生产者是绿色植物；在海洋和湖泊中，藻类和浮游植物是主要生产者。
s is: carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll.
它们通过光合作用将二氧化碳和水转化为葡萄糖和氧气。光合作用的文字方程式是：二氧化碳 + 水 → 葡萄糖 + 氧气，需要光和叶绿素。
Because producers make the first usable energy store in an ecosystem, every food chain must begin with a producer.
由于生产者制造生态系统中第一个可用的能量储存，每条食物链都必须以生产者开始。
3. Primary, Secondary and Tertiary Consumers | 初级、次级和三级消费者
Consumers cannot make their own food, so they must eat other organisms. A primary consumer eats producers and is usually a herbivore, such as a rabbit or caterpillar.
消费者不能自己制造食物，所以必须吃其他生物。初级消费者吃生产者，通常是食草动物，例如兔或毛虫。
A secondary consumer eats primary consumers. It is often a carnivore, such as a fox that eats rabbits, but it can also be an omnivore.
次级消费者吃初级消费者。它通常是食肉动物，例如吃兔子的狐狸，但也可能是杂食动物。
A tertiary consumer eats secondary consumers. In a four-link chain, it is the top predator. Examples include an eagle that eats a snake, or a shark that eats large fish.
三级消费者吃次级消费者。在四环节食物链中，它是顶级捕食者。例如吃蛇的鹰，或吃大鱼的大型鲨鱼。
We can label each feeding level with a number: producer (first trophic level), primary consumer (second), secondary consumer (third), and tertiary consumer (fourth).
我们可以为每个取食层级编号：生产者（第一营养级）、初级消费者（第二营养级）、次级消费者（第三营养级）和三级消费者（第四营养级）。
4. Decomposers: Nature's Recyclers | 分解者：自然界的回收者
Decomposers are organisms that break down dead plants and animals, as well as waste materials. The main decomposers are bacteria and fungi.
分解者是分解死去的动植物以及废物的生物。主要分解者是细菌和真菌。
They release enzymes onto dead matter and absorb the digested nutrients. This process returns mineral ions, such as nitrates and phosphates, to the soil, which producers need for growth.
它们向死亡物质释放酶，并吸收消化后的营养物质。这个过程将硝酸盐和磷酸盐等矿物离子归还土壤，供生产者生长所需。
Without decomposers, nutrients would remain locked inside dead bodies, and soils would become poor. Decomposers are therefore essential for recycling matter in an ecosystem.
没有分解者，营养物质将被锁在尸体中，土壤会变得贫瘠。因此分解者对生态系统中物质的循环至关重要。
5. What is a Food Web? | 什么是食物网？
A food web is a network of interconnected food chains. Most organisms eat more than one type of food and are eaten by more than one predator, so a single chain is too simple to describe a real community.
食物网是相互连接的食物链网络。大多数生物吃不止一种食物，也被不止一种捕食者吃掉，因此单一食物链过于简单，无法描述真实的群落。
For example, in a woodland, a vole may eat grass, seeds and insects. It may be eaten by an owl, a fox or a weasel. These multiple links form a branching web rather than one straight line.
例如，在林地中，田鼠可能吃草、种子和昆虫。它可能被猫头鹰、狐狸或黄鼠狼吃掉。这些多重联系形成一个分支网络，而不是一条直线。
If one species in a food web is removed, the effects can spread along many chains. Food webs therefore help ecologists predict how a change in one population may affect others.
如果食物网中的一个物种被移除，其影响会沿多条食物链传播。因此食物网帮助生态学家预测一个种群的变化如何影响其他种群。
6. Energy Flow and the 10% Rule | 能量流动与10%法则
Energy enters most ecosystems as sunlight and is captured by producers during photosynthesis. It then flows along a food chain as one organism eats another.
能量以阳光形式进入大多数生态系统，被生产者在光合作用中捕获。然后当一种生物吃另一种生物时，能量沿食物链流动。
At each trophic level, only about 10% of the energy is passed on to the next level. The other 90% is used for life processes such as movement, growth and respiration, or is lost as heat to the surroundings.
在每个营养级，只有约10%的能量传递到下一级。其余90%用于生命活动，如运动、生长和呼吸，或作为热量散失到周围环境中。
Energy transferred to next level ≈ 10% of energy taken in
传递到下一级的能量 ≈ 摄入能量的10%
This energy loss explains why food chains are short and why top predators are rare. A large area of producers is needed to support only a few top carnivores.
这种能量损失解释了食物链为何较短，以及顶级捕食者为何稀少。需要大面积的 producers 才能养活少数顶级食肉动物。
7. Trophic Levels and Pyramids of Numbers/Biomass | 营养级与数量/生物量金字塔
A trophic level is the position an organism occupies in a food chain. Producers form the first level, primary consumers the second, secondary consumers the third, and so on.
营养级是生物在食物链中所处的位置。生产者构成第一级，初级消费者第二级，次级消费者第三级，以此类推。
We can draw pyramids to represent feeding levels. A pyramid of numbers shows how many individual organisms are at each level. Often the base is widest, but a single large tree can support many insects, making the pyramid inverted or uneven.
我们可以绘制金字塔来表示取食层级。数量金字塔显示每一级有多少个生物个体。通常底部最宽，但一棵大树可以养活许多昆虫，使金字塔倒置或不规则。
A pyramid of biomass shows the total dry mass of living material at each level. It is usually pyramid-shaped because producers have the greatest total biomass. However, some aquatic pyramids of biomass can be inverted over short time periods.
生物量金字塔显示每一级生物的总干重。它通常呈金字塔形，因为生产者总生物量最大。但某些水生生物量金字塔在短时间内可能倒置。
Energy pyramids are always upright because energy is always lost at each transfer, so less energy is available at higher levels.
能量金字塔总是正立的，因为每次传递都会损失能量，因此更高营养级可用的能量更少。
8. Predator-Prey Relationships | 捕食者与猎物关系
A predator is an animal that hunts and kills other animals for food. Prey is the animal that is hunted. The populations of predators and prey are closely linked.
捕食者是猎杀其他动物为食的动物。猎物是被捕食的动物。捕食者和猎物的种群数量密切相关。
In a classic pattern, when prey numbers rise, predator numbers rise after a short delay because there is more food. As predators eat more prey, the prey population falls. Then predator numbers fall because food is scarce, allowing the prey population to recover. This creates repeating cycles.
在典型模式中，当猎物数量上升时，捕食者数量会在短暂延迟后上升，因为有更多食物。随着捕食者吃掉更多猎物，猎物种群下降。然后由于食物短缺，捕食者数量下降，使猎物种群得以恢复。这形成重复的周期。
Real population graphs show peaks and troughs that follow each other. The predator peak usually occurs slightly after the prey peak.
实际的种群数量图显示出相互跟随的波峰和波谷。捕食者的峰值通常略晚于猎物的峰值。
Published by TutorHao | KS3 Revision Series | aleveler.com
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