📚 Ecology Essentials for IB and AQA Science | IB AQA 科学：生态系统 考点精讲
Welcome to your comprehensive revision guide on ecosystems for IB and AQA Science. Whether you are preparing for IB Biology, AQA GCSE Combined Science or A-level Biology, understanding how living organisms interact with each other and their physical environment is fundamental. This article breaks down the key concepts, from energy flow and nutrient cycling to population dynamics and human impacts, with paired English–Chinese explanations to reinforce your learning.
欢迎阅读 IB 和 AQA 科学生态系统的综合复习指南。无论你正在准备 IB 生物学、AQA GCSE 综合科学还是 A-level 生物学，理解生物体如何相互影响并与自然环境相互作用都是基础。本文分解了从能量流动和养分循环到种群动态和人类影响的关键概念，并提供英汉对照的解释来强化学习。
1. Defining an Ecosystem | 生态系统的定义
An ecosystem is a dynamic complex of plant, animal and microorganism communities interacting with the non-living environment as a functional unit. It includes biotic factors such as producers, consumers and decomposers, as well as abiotic factors like temperature, water, light and soil pH. Ecosystems can be as small as a pond or as large as a tropical rainforest, but all are characterised by the flow of energy and the cycling of matter.
生态系统是由植物、动物和微生物群落与非生物环境相互作用构成的功能整体。它包括生物因素（如生产者、消费者和分解者）以及非生物因素（如温度、水分、光照和土壤 pH 值）。生态系统可以小至一个池塘，大至热带雨林，但所有生态系统的特征都是能量流动和物质循环。
The boundary of an ecosystem is often defined by the researcher, and it is important to remember that ecosystems are open systems that exchange energy and matter with their surroundings. In both IB and AQA specifications, students are expected to be able to identify abiotic and biotic components and explain how they influence community structure.
生态系统的边界通常由研究者界定，重要的是要记住生态系统是与周围环境交换能量和物质的开放系统。在 IB 和 AQA 大纲中，学生应能够识别非生物和生物组分，并解释它们如何影响群落结构。
2. Energy Flow and Trophic Levels | 能量流动与营养级
Energy enters most ecosystems through sunlight captured by autotrophs (producers) during photosynthesis. This chemical energy is then transferred between organisms in a food chain or food web. Each step in the chain is called a trophic level: producers (level 1), primary consumers (herbivores, level 2), secondary consumers (carnivores, level 3), and so on. Decomposers break down dead organic matter, releasing nutrients back into the soil.
能量通过光合作用中自养生物（生产者）捕获的阳光进入大多数生态系统。这些化学能随后在食物链或食物网中的生物之间传递。食物链中的每一级称为营养级：生产者（第一级）、初级消费者（食草动物，第二级）、次级消费者（食肉动物，第三级），依此类推。分解者分解死亡的有机物质，将养分释放回土壤。
A key principle is that energy transfer between trophic levels is inefficient—on average only about 10% of the energy at one level is converted into biomass at the next. This limits the length of food chains and explains the pyramid of energy, which is always upright. Students should be able to calculate the efficiency of energy transfer using the formula:
一个关键原则是营养级之间的能量传递效率低下——平均只有约 10% 的能量从一级转化为下一级的生物量。这限制了食物链的长度，并解释了能量金字塔总是呈正立形状的原因。学生应能使用公式计算能量传递效率：
Efficiency (%) = (Energy in higher trophic level ÷ Energy in lower trophic level) × 100
效率（%）=（较高营养级的能量 ÷ 较低营养级的能量）× 100
3. Food Chains and Food Webs | 食物链与食物网
A food chain is a linear sequence showing what eats what in an ecosystem, while a food web is a more realistic network of interconnected food chains. Food webs illustrate that most organisms consume more than one type of food and are consumed by several different predators. This complexity provides stability to ecosystems, because if one species declines, alternative food sources remain available for predators.
食物链是显示生态系统中“谁吃谁”的线性序列，而食物网是相互连接的食物链组成的更真实的网络。食物网表明，大多数生物食用不止一种食物，并被多种不同的捕食者所捕食。这种复杂性为生态系统提供了稳定性，因为如果一种物种数量下降，捕食者仍可获取替代食物来源。
In both IB and AQA exams, you need to be able to construct and interpret food chains and food webs, label trophic levels, and predict the effects of removing or adding a species. The terms autotroph, heterotroph, herbivore, carnivore, omnivore and detritivore are essential vocabulary.
在 IB 和 AQA 考试中，你需要能够构建和解读食物链和食物网、标注营养级，并预测移除或增加一个物种的影响。自养生物、异养生物、食草动物、食肉动物、杂食动物和食碎屑动物等术语是必备词汇。
4. Pyramids of Numbers, Biomass and Energy | 数量、生物量和能量金字塔
Ecological pyramids provide a graphical representation of the structure of a food chain. A pyramid of numbers shows the count of individual organisms at each trophic level, but can be inverted (e.g. one tree supporting many insects). A pyramid of biomass displays the dry mass of living material, which is usually upright but can also be inverted in aquatic ecosystems where phytoplankton have a low biomass but rapid turnover.
生态金字塔提供了食物链结构的图形表示。数量金字塔显示每个营养级的个体数量，但可能是倒置的（例如一棵树支持许多昆虫）。生物量金字塔显示活物质的干重，它通常呈正立形状，但在水生生态系统中也可能倒置，因为浮游植物生物量低但周转快。
The pyramid of energy, however, is always upright because it represents the flow of energy over time, and energy is always lost as heat to the environment at each trophic level. Understanding these pyramids helps explain the limitations on top predators and why ecosystems can only support a small biomass of carnivores.
然而，能量金字塔总是呈正立形状，因为它表示一段时间内的能量流动，且能量在每个营养级总是以热的形式散失到环境中。理解这些金字塔有助于解释顶级捕食者的限制，以及为什么生态系统只能支持较小的食肉动物生物量。
5. Nutrient Cycles: Carbon and Nitrogen | 养分循环：碳循环和氮循环
Unlike energy, matter is recycled within an ecosystem. The carbon cycle involves the movement of carbon between the atmosphere, organisms, oceans and rock. Key processes include photosynthesis (CO₂ fixed into organic carbon), respiration (return of CO₂), decomposition, combustion and sedimentation. Human activities such as burning fossil fuels and deforestation have altered the carbon cycle, contributing to global warming.
与能量不同，物质在生态系统内循环。碳循环涉及碳在大气、生物体、海洋和岩石之间的运动。关键过程包括光合作用（CO₂ 被固定为有机碳）、呼吸作用（释放 CO₂）、分解、燃烧和沉积。燃烧化石燃料和砍伐森林等人类活动改变了碳循环，导致全球变暖。
The nitrogen cycle is equally important for building proteins and nucleic acids. It involves nitrogen fixation (by bacteria or lightning), nitrification, assimilation, ammonification and denitrification. Students should be able to name key bacteria: nitrogen-fixing bacteria (e.g. Rhizobium in legume root nodules), nitrifying bacteria (Nitrosomonas, Nitrobacter) and denitrifying bacteria.
氮循环对于构建蛋白质和核酸同样重要。它涉及固氮作用（由细菌或闪电完成）、硝化作用、同化作用、氨化作用和反硝化作用。学生应能说出关键细菌的名称：固氮细菌（例如豆科植物根瘤中的根瘤菌）、硝化细菌（亚硝化单胞菌、硝化杆菌）和反硝化细菌。
Both cycles appear frequently in IB and AQA exam questions, often with diagrams to label or gaps to fill.
这两个循环经常出现在 IB 和 AQA 试题中，通常需要标注图表或填写空缺。
6. Biotic Interactions: Competition, Predation and Symbiosis | 生物相互作用：竞争、捕食和共生
Organisms do not exist in isolation; they are connected through various interactions. Competition occurs when two or more individuals require the same limited resource—this can be intraspecific (within the same species) or interspecific (between different species). Competition reduces the fitness of all involved and can drive natural selection.
生物并非孤立存在；它们通过多种相互作用联系在一起。当两个或更多个体需要相同的有限资源时，就会发生竞争——这可以是种内竞争（同一物种内）或种间竞争（不同物种间）。竞争降低了所有参与者的适合度，并可以推动自然选择。
Predation is a feeding relationship where one organism (the predator) kills and eats another (the prey). Predator-prey cycles often show oscillations, which can be examined through graphical data. Symbiosis refers to close and long-term interactions: mutualism (both benefit, e.g. coral and zooxanthellae), commensalism (one benefits, the other unaffected) and parasitism (one benefits, the other harmed).
捕食是一种取食关系，其中一个生物（捕食者）杀死并吃掉另一个生物（猎物）。捕食者-猎物循环常呈现振荡，这可以通过图表数据来研究。共生指密切而长期的相互作用：互利共生（双方受益，如珊瑚和虫黄藻）、偏利共生（一方受益，另一方不受影响）和寄生（一方受益，另一方受害）。
7. Population Growth and Carrying Capacity | 种群增长与环境容纳量
Populations change size over time depending on birth rate, death rate, immigration and emigration. In ideal conditions with unlimited resources, populations grow exponentially, producing a J-shaped curve. However, in reality, limiting factors such as food, space, disease and predation cause growth to slow and eventually stabilise. This results in a sigmoid (S-shaped) growth curve approaching the carrying capacity (K) of the environment.
种群大小随时间变化，取决于出生率、死亡率、迁入和迁出。在理想条件下资源无限时，种群呈指数增长，产生“J”形曲线。然而在现实中，食物、空间、疾病和捕食等限制因素导致增长减慢并最终稳定。这形成了接近环境容纳量（K）的“S”形（S型）增长曲线。
Carrying capacity is the maximum population size that can be sustained indefinitely in a given environment. Students must be able to interpret population growth graphs and identify phases: lag, exponential (log) growth, transitional and plateau. In IB, the concept of density-dependent and density-independent factors is also required.
环境容纳量是在给定环境中可以无限期维持的最大种群大小。学生必须能够解读种群增长图并识别各个阶段：滞缓期、指数增长期、过渡期和平稳期。在 IB 课程中，还需要掌握密度制约因素和非密度制约因素的概念。
8. Ecological Succession | 生态演替
Ecological succession is the gradual, directional change in the species structure of an ecological community over time. Primary succession occurs in lifeless areas where no soil exists, such as bare rock after a volcanic eruption. Pioneer species like lichens and mosses colonise first, breaking down rock and forming soil. This allows grasses, shrubs and eventually trees to establish, leading to a climax community.
生态演替是生态群落物种结构随时间发生的渐进的、有方向的变化。原生演替发生在没有土壤的无生命区域，例如火山喷发后的裸岩。地衣和苔藓等先锋物种首先定植，分解岩石并形成土壤。这使草本植物、灌木并最终使树木得以生长，形成顶极群落。
Secondary succession happens where an existing community has been disturbed (e.g. by fire or farming) but soil remains intact. This process is faster because seeds, roots and soil organisms are already present. Both types of succession are examinable, and students should be able to describe the changes in biodiversity, biomass and soil depth over time.
次生演替发生在现有群落受到干扰（如火灾或耕作）但土壤保持完整的地方。这一过程较快，因为种子、根系和土壤生物已经存在。两种演替类型都在考试范围内，学生应能够描述生物多样性、生物量和土壤深度随时间的变化。
9. Biodiversity and Its Measurement | 生物多样性及其测量
Biodiversity encompasses the variety of life at all levels: genetic diversity within a species, species diversity within a community, and ecosystem diversity across the planet. High biodiversity often indicates a healthy, stable ecosystem. Key ways to measure species diversity include species richness (number of different species) and species evenness (relative abundance of each species).
生物多样性涵盖各个层次的生命多样性：物种内的遗传多样性、群落内的物种多样性，以及全球范围的生态系统多样性。高生物多样性通常表示一个健康、稳定的生态系统。衡量物种多样性的关键方法包括物种丰富度（不同物种的数量）和物种均匀度（每个物种的相对丰度）。
A commonly used index in IB Biology is Simpson’s diversity index:
IB 生物学中常用的指数是辛普森多样性指数：
D = N(N – 1) / Σ n(n – 1)
where N is the total number of organisms and n is the number of individuals of each species. A higher D value indicates greater diversity. Students should be able to calculate this and compare different communities. AQA specifications also expect students to understand the importance of biodiversity for ecosystem services and human well-being.
其中 N 是生物总数，n 是每个物种的个体数。D 值越高表示多样性越大。学生应能计算并比较不同群落。AQA 大纲也要求学生理解生物多样性对生态系统服务和人类福祉的重要性。
10. Human Impacts on Ecosystems | 人类对生态系统的影响
Human activities can drastically alter ecosystems. Deforestation, urbanisation, agriculture and pollution reduce biodiversity, fragment habitats and disrupt nutrient cycles. The release of excess nitrates and phosphates from fertilisers can cause eutrophication in water bodies, leading to algal blooms, oxygen depletion and fish death. Acid rain, resulting from SO₂ and NOₓ emissions, damages forests and aquatic life.
人类活动可以极大地改变生态系统。砍伐森林、城市化、农业和污染减少了生物多样性，使栖息地破碎化，并扰乱了养分循环。化肥中过量硝酸盐和磷酸盐的释放可引起水体富营养化，导致藻华、缺氧和鱼类死亡。由 SO₂ 和 NOₓ 排放引起的酸雨会损害森林和水生生物。
Climate change, driven by greenhouse gas emissions, is altering temperature and precipitation patterns, forcing species to migrate, adapt or face extinction. In both IB and AQA, students must evaluate the evidence for human-induced environmental change and discuss conservation strategies such as setting up nature reserves, captive breeding programmes and international agreements.
由温室气体排放驱动的气候变化正在改变温度和降水模式，迫使物种迁徙、适应或面临灭绝。在 IB 和 AQA 课程中，学生必须评估人类引起环境变化的证据，并讨论保护策略，如建立自然保护区、圈养繁殖计划和国际协议。
11. Conservation and Sustainable Management | 保护与可持续管理
Conservation aims to maintain biodiversity and ecosystem functions for future generations. Approaches range from in situ conservation (protecting species within their natural habitat, e.g. national parks) to ex situ conservation (protecting species outside their habitat, e.g. seed banks, zoos). Sustainable management uses resources in ways that meet current needs without compromising the ability of future generations to meet theirs.
保护旨在为后代维持生物多样性和生态系统功能。方法包括就地保护（在自然栖息地内保护物种，如国家公园）和迁地保护（在栖息地外保护物种，如种子库、动物园）。可持续管理以既满足当前需求又不损害后代满足其自身需求的能力的方式利用资源。
Examples of sustainable practices include sustainable forestry (selective logging, replanting), sustainable fisheries (quotas, mesh size limits) and integrated pest management. Students should be able to apply the principles of conservation to specific case studies, such as the preservation of tropical rainforests or coral reefs.
可持续实践的实例包括可持续林业（择伐、重新种植）、可持续渔业（配额、网目尺寸限制）和综合害虫管理。学生应能将保护原则应用于具体案例研究，例如热带雨林或珊瑚礁的保护。
12. Fieldwork and Sampling Techniques | 野外调查与取样技术
Investigating ecosystems often requires fieldwork. Common sampling methods include quadrats (for estimating the abundance and distribution of plants or slow-moving animals) and transects (for studying changes along a gradient). A belt transect uses a series of quadrats at regular intervals to show zonation, for example on a rocky shore.
研究生态系统常常需要野外调查。常见的取样方法包括样方（用于估计植物或缓慢移动动物的丰度和分布）和样带（用于研究沿梯度的变化）。带状样带以规则间隔使用一系列样方来显示带状分布，例如在岩石海岸上。
Animals can be sampled using pitfall traps, sweep nets, pooters and mark-release-recapture techniques for mobile species. The Lincoln index estimates population size:
动物可以使用陷阱、扫网、吸虫器以及对移动物种使用标记重捕技术进行取样。林肯指数用于估计种群大小：
N = (M × C) / R
where N = population size, M = number marked and released, C = total caught in second sample, R = number of marked individuals recaptured. Ethical considerations and minimising disturbance are also part of the IB and AQA practical skills requirements.
其中 N = 种群大小，M = 标记并释放的数量，C = 第二次取样中捕获的总数，R = 重新捕获的标记个体数。伦理考量与减少干扰也是 IB 和 AQA 实验技能要求的一部分。
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