摄食关系
生物学· 4.6–4.9（2017年第3版考纲）· 15 分钟阅读
1. 摄食关系中的营养级★★☆☆☆⏱ 3 min
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营养级
某一生物在摄食序列中所处的位置，由其营养来源决定。
Producer: Autotrophic (usually green plant) that makes food via photosynthesis, forming the base of all feeding sequences
Primary consumer: Herbivore that eats producers
Secondary consumer: Organism that eats primary consumers
Tertiary consumer: Apex predator that eats secondary consumers
Decomposer: Bacteria/fungi that break down dead organisms and waste to recycle nutrients
写出以下序列中每种生物所属的营养级：草 → 毛毛虫 → 麻雀 → 鹰
- 1
- 草通过光合作用合成自身所需有机物 = 生产者
- 2
- 毛毛虫以草为食（植食性）= 初级消费者
- 3
- 麻雀以毛毛虫为食 = 次级消费者
- 4
- 鹰以麻雀为食 = 三级消费者
- 5
- 分解者会分解该序列中所有营养级的死亡生物个体和代谢废物
Exam tip:
标准食物链中通常不会画出分解者，但如果题目要求列出某一生态系统的所有营养级，你必须明确提及分解者。
2. 食物链与食物网★★☆☆☆⏱ 4 min
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食物链
展示生物之间能量、生物量和养分传递的线性序列，箭头方向从被捕食者指向捕食者。
食物网是由多条相互关联的食物链组成的网络，展示了某一生态系统中所有的摄食关系。大多数生物拥有多种食物来源，因此食物网比简单的线性食物链更能准确反映真实生态系统的情况。
某学生画出的序列为：狐狸 → 兔子 → 草。请指出其中的错误并修正该序列。
- 1
- 箭头方向颠倒，意味着能量从狐狸流向兔子再流向草，这是错误的。
- 2
- 草被兔子取食，兔子被狐狸捕食，因此箭头应当从被捕食的生物指向取食它的生物。
- 3
- 正确序列：草 → 兔子 → 狐狸
3. 生态金字塔★★★☆☆⏱ 4 min
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生态金字塔展示了摄食序列中每个营养级对应的某一参数的相对数值。考试要求你区分以下三种核心类型：
Pyramid Type | What it measures | Can it be inverted? |
|---|---|---|
Pyramid of number | Count of individual organisms at each level | Yes (e.g. 1 large tree supporting 1000+ insects) |
Pyramid of biomass | Total dry mass of organisms per unit area at each level | Rarely, almost always upright |
Pyramid of energy | Total energy available at each level per unit time | No, always upright |
解释为什么即便同一生态系统的数量金字塔可以倒置，能量金字塔也永远不可能倒置。
- 1
- 能量在每一个营养级都会损失：包括呼吸作用以热量形式散失、随代谢废物流失、或是用于运动消耗。
- 2
- 较高营养级可利用的总能量始终低于其下一个营养级的总能量。
- 3
- 数量金字塔统计生物个体数量，因此一株体型极大的生产者可以供养数百个体型更小的消费者，使金字塔呈倒置形态，但这一规律不适用于可利用总能量的变化。
Exam tip:
如果题目要求比较不同类型的金字塔，一定要将能量损失作为能量金字塔始终呈正立形态的核心原因进行阐述。
4. 能量传递与10%法则★★★☆☆⏱ 4 min
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10%能量传递法则
某一营养级生物量中储存的能量约有10%会传递到下一个营养级，剩余90%的能量会从食物链中散失。
Key reasons for energy loss between levels: energy used in respiration (released as heat to surroundings), energy used for movement, energy lost in undigested faeces (egestion), energy lost in urine (excretion), not all parts of the organism are eaten by consumers
Only energy used to build new biomass is passed on to the next trophic level
若某食物链的生产者营养级储存了50000 kJ的能量，计算次级消费者营养级可获得的能量为多少。
- 1
- 生产者能量的10%传递给初级消费者： kJ
- 2
- 初级消费者能量的10%传递给次级消费者： kJ
- 3
- 最终答案：500 kJ
Exam tip:
要求说明能量损失原因的考题通常需要答出2~3个有效要点才能得满分，因此请至少掌握上文列出的3个标准原因。
5. 常见陷阱
错误做法:
Drawing food chain arrows from predator to prey
原因:
Arrows represent energy flow from the eaten organism to the eater, not the direction of consumption action.
正确做法:
Always point arrows from the organism being consumed to the consumer (prey → predator).
错误做法:
Stating pyramids of biomass are always upright
原因:
Rare inverted cases exist, e.g. aquatic ecosystems where phytoplankton biomass fluctuates seasonally below zooplankton biomass.
正确做法:
State that pyramids of biomass are usually upright; only pyramids of energy are always upright.
错误做法:
Only referencing energy flow in feeding relationships, not substances
原因:
The spec explicitly requires you to understand transfer of both energy and substances (nutrients/carbon) along food chains.
正确做法:
Mention both energy flow and nutrient/substance transfer when describing feeding relationships.
错误做法:
Listing only 1 reason for energy loss between trophic levels
原因:
Exam questions usually require 2–3 valid reasons for full marks.
正确做法:
Memorize 3+ standard reasons: respiratory heat loss, egestion of undigested food, not all parts of the organism are eaten.
错误做法:
Including decomposers as a single level on energy pyramids
原因:
Decomposers break down waste from every trophic level, they do not occupy a single linear position in standard pyramids.
正确做法:
Only reference decomposers as separate to the linear producer-tertiary consumer sequence unless explicitly asked.
6. 速查表
Concept | Key Exam Fact | Example |
|---|---|---|
Trophic level order | Producer → Primary consumer → Secondary consumer → Tertiary consumer | Grass → Grasshopper → Frog → Hawk |
Food chain arrows | Point in direction of energy flow (eaten → eater) | Grass → Rabbit (energy flows from grass to rabbit) |
Pyramid of number | Can be inverted | 1 oak tree → 1000 caterpillars |
10% energy rule | ~10% of energy passed between trophic levels | 10,000 kJ producers → 1000 kJ primary consumers → 100 kJ secondary consumers |
Energy loss reasons | Respiratory heat, egestion, excretion, uneaten parts | Warm-blooded animals lose large amounts of energy as heat via respiration |
7. 常见问题
为什么能量金字塔始终呈正立形态？
能量在每一个营养级都会通过呼吸作用、热量散失、代谢废物等途径损失，因此更高营养级可利用的总能量始终低于其下一级，该规律不存在例外情况。
食物链中包含分解者吗？
大多数标准的线性食物链不会明确画出分解者，但分解者存在于所有生态系统中，负责分解来自各个营养级的代谢废物和死亡生物个体。
为什么食用植物性饮食的能量利用效率更高？
植物性饮食意味着人类直接以生产者营养级为食，与食用更高营养级的肉类相比，能量从来源到消费者的过程中损失的能量要少得多。
深入阅读
下一步
Now that you have mastered feeding relationships, you are ready to move on to nutrient cycling, which covers how decomposers recycle carbon and nitrogen through ecosystems — a closely linked topic that is often tested alongside feeding relationships in extended response questions. You should also practice applying the 10% energy transfer rule to exam-style calculation questions, and learn to interpret complex food webs to identify trophic levels for different organisms. Understanding these concepts will also prepare you for later topics on human impacts on ecosystems, including overfishing and deforestation, which draw heavily on energy transfer and feeding relationship principles.