Ecology Key Points for AQA Biology | IB AQA 生物：生态学考点精讲

📚 Ecology Key Points for AQA Biology | IB AQA 生物：生态学考点精讲

Ecology is a core topic in AQA A-level Biology, exploring the interactions between organisms and their environment at population, community and ecosystem levels. It integrates quantitative skills with fundamental concepts such as energy flow, nutrient cycling and succession. This revision guide distils key AQA exam points into bilingual sections, covering everything from sampling methods to the nitrogen cycle, and will help you build confidence for both data-handling and extended-response questions.

生态学是 AQA A-level 生物学的核心主题，探讨生物与环境在种群、群落和生态系统层面的相互作用。它把定量技能与能量流动、物质循环和演替等基本概念有机结合起来。这份复习指南提炼了 AQA 的考试要点，用中英双语分节讲解，涵盖从取样方法到氮循环的所有重点，助你从容应对数据分析与长篇论述题。

1. Introduction to Ecosystems | 生态系统简介

An ecosystem consists of all the living organisms (biotic factors) in a particular area, together with the non-living (abiotic) components such as temperature, light, water and soil pH. The key ecological levels are individual, population, community and ecosystem. A population is a group of individuals of the same species living in the same area at the same time. A community comprises all the populations of different species in a habitat. The habitat is the place where an organism lives, while its niche describes its role in the ecosystem, including its interactions with other organisms and its use of resources.

生态系统由特定区域内的所有生物（生物因子）和非生物环境（非生物因子，如温度、光照、水分和土壤 pH）共同构成。生态学研究的重点层次包括个体、种群、群落和生态系统。种群是同一时期生活在同一区域的同种个体的集合；群落则是一个栖息地中所有不同物种种群的总和。栖息地是生物生活的地点，而生态位则描述了生物在生态系统中的角色，包括它与其他生物的相互作用以及对资源的利用方式。

2. Energy Flow and Trophic Levels | 能量流动与营养级

Energy enters most ecosystems as sunlight and is captured by producers (photoautotrophs) during photosynthesis. This chemical energy is then transferred along food chains via feeding relationships. A trophic level describes the position an organism occupies in a food chain. Producers form the first trophic level, primary consumers the second, secondary consumers the third, and so on. Energy transfer between trophic levels is inefficient — typically only about 10% of the energy is passed on, while the rest is lost as heat from respiration, excreted as waste, or remains uneaten.

大多数生态系统的能量以阳光的形式进入，由生产者（光合自养生物）通过光合作用固定。化学能随后沿食物链通过取食关系传递。营养级描述了生物在食物链中所处的位置：生产者构成第一营养级，初级消费者为第二级，次级消费者为第三级，依此类推。营养级之间的能量传递效率很低——通常只有约 10% 的能量进入下一个营养级，其余能量则通过呼吸作用以热的形式散失、作为废物排出或被遗留在未取食的部分。

Students must be able to calculate the efficiency of energy transfer between trophic levels using the formula:

考生需掌握营养级间能量传递效率的计算：

Efficiency (%) = (energy in new biomass after transfer ÷ energy available before transfer) × 100

In exam questions, you are often given data on gross primary production (GPP), net primary production (NPP) and respiration (R). Remember the relationship: NPP = GPP − R. NPP represents the energy available to the next trophic level as plant biomass. Similar calculations apply to consumers using gross secondary production and net secondary production.

考试题中常给出总初级生产量（GPP）、净初级生产量（NPP）和呼吸消耗（R）。需牢记：NPP = GPP − R。NPP 代表可供下一个营养级利用的植物生物量中的能量。消费者的能量传递也可类似地通过总次级生产量和净次级生产量计算。

3. Ecological Pyramids and Production Efficiency | 生态金字塔与生产效率

Ecological pyramids are graphical representations of the structure of an ecosystem. There are three common types: pyramids of numbers, pyramids of biomass, and pyramids of energy. Pyramids of energy are always upright, because energy is always lost between trophic levels; they display the rate of energy flow over time, usually in kJ m⁻² year⁻¹. Pyramids of numbers can be inverted, for example, when one large tree supports many insects. Pyramids of biomass can also be inverted in aquatic ecosystems, where phytoplankton have a small standing biomass but reproduce very rapidly.

生态金字塔是生态系统结构的图示表示，常见类型有数量金字塔、生物量金字塔和能量金字塔。能量金字塔始终呈正立形，因为能量在营养级之间总会损耗；它以 kJ m⁻² year⁻¹ 为单位显示能量流动速率。数量金字塔可能出现倒置，例如一棵大树承载许多昆虫。生物量金字塔在水生生态系统中也可能倒置，因为浮游植物现存生物量虽小，但繁殖极为迅速。

AQA expects students to interpret pyramid diagrams and explain why energy pyramids are the most accurate representation of energy flow. You should also link the shape of pyramids to production efficiency and the length of food chains — limited energy transfer usually restricts food chains to about 4–5 trophic levels.

AQA 考试要求学生解读金字塔示意图，并能解释为何能量金字塔能最准确地反映能量流动。同时，还需将金字塔的形状与生产效率和食物链长度联系起来——有限的能量传递通常使食物链限制在约 4–5 个营养级。

4. Sampling Techniques for Populations | 种群取样技术

To study the distribution and abundance of organisms, ecologists use sampling methods. Random sampling with quadrats is used for sessile or slow-moving organisms in a uniform habitat. A quadrat is a square frame of known area (e.g. 1 m²), laid randomly using random number coordinates. Systematic sampling along a transect is employed when there is an environmental gradient, such as a change from a shaded area to an open field. A belt transect involves placing quadrats at regular intervals along a line and recording species presence, abundance or percentage cover.

为了研究生物的分布和丰度，生态学家使用取样方法。在均一栖息地中对营固着或缓慢移动生活的生物采用随机样方取样。样方是已知面积（如 1 m²）的方框，用随机数字坐标随机放置。当存在环境梯度（如从遮阴地带到开阔地的变化）时，则沿样线进行系统取样。带型样带（belt transect）是指沿一条线每隔固定间隔放置样方，记录物种的存在、多度或盖度百分比。

For mobile animals, mark-release-recapture is used. To obtain reliable estimates, it is essential that the marking does not affect the animal’s survival or behaviour, that marks are not lost, and that the released sample has time to mix randomly with the population. The Lincoln index is the standard calculation.

对活动性较强的动物，则采用标记重捕法。要获得可靠的估算，必须确保标记不影响动物的存活或行为、标记不会丢失，并且释放的样本有时间与种群随机混合。林肯指数是标准的计算方式。

5. Mark-Release-Recapture Method | 标记重捕法

The Lincoln index equation estimates population size:

林肯指数公式用于估算种群大小：

N = (n₁ × n₂) / m

where N = estimated total population, n₁ = number of individuals caught and marked in the first sample, n₂ = number of individuals caught in the second sample, m = number of marked individuals recaptured in the second sample. The method assumes that the population is closed, that marking does not affect survival, and that marked and unmarked individuals mix completely.

式中 N = 估算的种群总数，n₁ = 第一次捕捉并标记的个体数，n₂ = 第二次捕捉的个体数，m = 第二次捕捉中已标记的个体数。该方法假设种群是封闭的，标记不影响存活，且标记和未标记个体充分混合。

Examiners frequently ask students to evaluate the assumptions and suggest why real estimates might be inaccurate — for example, migration, births and deaths, or loss of marks. You may also need to calculate percentage error or compare estimates obtained under different conditions.

考官常要求学生评价假设条件，并分析为何实际估算可能不准确——例如迁移、出生和死亡，或标记脱落。也可能要求计算百分误差，或比较不同条件下的估算结果。

6. Population Growth Models | 种群增长模型

Populations in ideal conditions grow exponentially: this J-shaped curve can be described by dN/dt = rN, where r is the intrinsic rate of increase. Exponential growth cannot continue indefinitely because resources become limiting. Logistic growth introduces a carrying capacity (K), producing an S-shaped (sigmoid) curve. The logistic equation includes a factor (K − N)/K, which slows growth as N approaches K.

在理想条件下，种群呈指数增长，形成 J 形曲线，可用 dN/dt = rN 描述，其中 r 是内禀增长率。然而指数增长不可能无限持续，因为资源会变得有限。逻辑斯谛增长引入了环境容纳量（K），产生 S 形（sigmoid）曲线。逻辑斯谛方程包含 (K − N)/K 这一因子，当 N 接近 K 时增长减缓。

AQA exam questions often present a graph of bacterial or yeast population growth, or data on reindeer or other introduced species. You must be able to identify the lag phase, log (exponential) phase, stationary phase and, where relevant, death phase, and link each phase to environmental resistance factors such as nutrient depletion, waste accumulation and disease.

AQA 考题常给出细菌或酵母种群增长图，或关于驯鹿等引入物种的数据。考生需学会识别延滞期、对数（指数）增长期、稳定期，以及可能出现的死亡期，并将各阶段与营养耗尽、废物积累和疾病等环境阻力因素联系起来。

7. Succession: Primary and Secondary | 生态演替：原生与次生

Succession is the directional change in a community of organisms over time. Primary succession begins on lifeless terrain where no soil exists, such as bare rock after a volcanic eruption. Pioneer species such as lichens and mosses colonise first, breaking down the rock and beginning soil formation. Over time, herbs, shrubs and finally climax vegetation such as woodland develop, accompanied by increasing biodiversity, deeper soil and greater biomass. Secondary succession occurs on previously inhabited land where soil is already present, for example, after a forest fire or land abandonment; it typically proceeds much faster.

演替是指生物群落随时间发生的有方向性的变化。原生演替起始于不存在土壤的无生命地面，如火山喷发后的裸岩。地衣和苔藓等先锋物种首先定居，分解岩石并开始形成土壤。随着时间推移，草本植物、灌木，最后是顶极植被（如林地）依次发展，生物多样性增加，土壤层变厚，生物量增大。次生演替发生在已存在土壤的原有生境上，例如森林火灾后或弃耕地，其进程通常快得多。

You should know the terms sere, seral stages, pioneer community, climax community, and plagioclimax (a community prevented from reaching climatic climax by human activity such as grazing or burning). Data analysis may involve interpreting line graphs of species richness or soil depth over time.

应掌握的术语包括：演替系列（sere）、演替阶段、先锋群落、顶极群落和偏途顶极（因放牧或焚烧等人为活动阻止气候顶极达到的群落）。数据分析可能涉及解读物种丰富度或土壤深度随时间变化的折线图。

8. Carbon Cycle | 碳循环

The carbon cycle is a key nutrient cycle that circulates carbon between the atmosphere, oceans, living organisms and geological stores. Carbon dioxide in the atmosphere is fixed by photosynthesis in plants and phytoplankton. Carbon is passed along food chains and returned to the atmosphere through respiration by all organisms. Decomposers (bacteria and fungi) break down dead organic matter and respire, releasing CO₂. Combustion of fossil fuels and wood releases stored carbon. In the oceans, CO₂ dissolves and enters solution, forming carbonate ions that can be used by marine organisms to build shells and coral, eventually forming limestone rock.

碳循环是重要的物质循环，碳在大气、海洋、生物和地质储存库间循环。大气中的二氧化碳通过植物和浮游植物的光合作用被固定。碳沿食物链传递，并通过所有生物的呼吸作用返回大气。分解者（细菌和真菌）分解死亡有机质并呼吸，释放 CO₂。化石燃料和木材的燃烧会释放储存的碳。在海洋中，CO₂ 溶解并形成碳酸根离子，海洋生物利用它们构建贝壳和珊瑚，最终形成石灰岩。

Exam questions often ask you to sketch the carbon cycle or label diagrams showing processes such as photosynthesis, respiration, decomposition, combustion, fossilisation and sedimentation. Be ready to discuss how deforestation and increased burning of fossil fuels disrupt the carbon cycle and contribute to climate change.

考题常要求绘制碳循环简图，或标出光合作用、呼吸作用、分解、燃烧、化石化和沉积等过程。要准备好探讨砍伐森林和化石燃料燃烧加剧如何干扰碳循环并加速气候变化。

9. Nitrogen Cycle | 氮循环

Nitrogen is essential for the synthesis of proteins and nucleic acids. The nitrogen cycle involves four main processes: nitrogen fixation, ammonification, nitrification and denitrification. Nitrogen fixation converts atmospheric N₂ into ammonia (NH₃) or ammonium ions (NH₄⁺); this can be carried out by free-living bacteria such as Azotobacter or by Rhizobium bacteria in root nodules of legumes. Lightning and the Haber process also fix a small amount.

氮是合成蛋白质和核酸所必需的元素。氮循环主要包括四个过程：固氮作用、氨化作用、硝化作用和反硝化作用。固氮作用将大气中的 N₂ 转化为氨（NH₃）或铵离子（NH₄⁺）；可由自由生活的固氮菌（如固氮菌属）或豆科植物根瘤中的根瘤菌完成。闪电和哈伯法也能固定少量氮。

Ammonification occurs when decomposers break down protein in dead matter and produce ammonium ions. Nitrification is a two-step aerobic process: nitrifying bacteria first oxidise ammonium to nitrite (NO₂⁻), e.g. Nitrosomonas, and then oxidise nitrite to nitrate (NO₃⁻), e.g. Nitrobacter. Denitrification, carried out by anaerobic bacteria such as Pseudomonas, reduces nitrates back to N₂ gas, returning nitrogen to the atmosphere. AQA expects you to know the roles of these named bacteria and the conditions that favour each process.

氨化作用由分解者分解死亡有机体中的蛋白质，产生铵离子。硝化作用是一个两步需氧过程：硝化细菌先将铵氧化为亚硝酸盐（NO₂⁻），如亚硝化单胞菌，再将其氧化为硝酸盐（NO₃⁻），如硝化杆菌。反硝化作用由厌氧细菌（如假单胞菌）将硝酸盐还原为氮气，使氮返回大气。AQA 考试要求记住这些具名细菌的作用以及有利于每一过程的条件。

10. Biodiversity and Simpson’s Index | 生物多样性与辛普森指数

Biodiversity can be measured at genetic, species and ecosystem levels. Species richness is the number of different species in a community, while species evenness reflects the relative abundance of each species. High biodiversity generally indicates a healthy, stable ecosystem. Simpson’s Index of Diversity (D) is a quantitative measure that takes both richness and evenness into account. The formula is:

生物多样性可从遗传、物种和生态系统三个层次衡量。物种丰富度指群落中不同物种的数目，物种均匀度则反映各物种的相对丰度。高生物多样性通常意味着一个健康、稳定的生态系统。辛普森多样性指数（D）是一种综合了丰富度和均匀度的定量指标，其公式为：

D = 1 − (Σ n(n−1) / N(N−1))

where n = number of individuals of each species, N = total number of individuals of all species. A high value of D (close to 1) indicates high diversity; a value close to 0 indicates low diversity. The nested calculation requires careful rounding to significant figures, as practised in AQA data questions.

式中 n = 每个物种的个体数，N = 所有物种的个体总数。D 值接近 1 表示多样性高，接近 0 表示多样性低。因为在 AQA 数据题中需要练习，嵌套计算时要仔细进行有效数字取舍。

Be prepared to interpret calculated Simpson’s Index values in the context of conservation or farming — for example, comparing a natural woodland (high D) with an intensively farmed wheat field (low D). Understand that monocultures reduce species diversity and make ecosystems more vulnerable to pests and disease.

要准备好结合保护或农业背景解读辛普森指数——例如，比较天然林地（高 D）与集约化麦田（低 D）。理解单一种植会降低物种多样性，使生态系统更易受病虫害威胁。

11. Agricultural Ecosystems and Sustainability | 农业生态系统与可持续性

Agricultural ecosystems are designed to maximise the yield of a desired product by manipulating energy flow and nutrient cycles. Practices such as the use of artificial fertilisers, pesticides, monoculture and selective breeding reduce the energy lost to pests and competing weeds, increasing net primary production available for human consumption. However, these practices often reduce biodiversity, cause eutrophication from fertiliser runoff, and deplete soil quality over time.

农业生态系统通过调控能量流动和养分循环，力求最大化目标产品的产量。使用人工化肥、农药、单一种植和选择育种等措施能减少流向害虫和竞争性杂草的能量损失，从而增加可供人类消费的净初级生产量。但这些做法常常降低生物多样性，导致化肥径流引发水体富营养化，并随时间损耗土壤质量。

Sustainable management strategies include crop rotation to maintain soil nitrogen, integrated pest management (IPM) to reduce chemical use, maintaining hedgerows and field margins to support pollinators and natural predators, and organic farming. AQA may provide data comparing the energy inputs and outputs of intensive and organic farming, requiring you to calculate efficiency and justify conservation measures.

可持续管理策略包括轮作以维持土壤氮素，综合病虫害管理（IPM）以减少化学品使用，保留树篱和田边带以支持传粉者和天敌，以及有机耕作。AQA 可能提供比较集约化农业和有机农业能量输入与输出的数据，要求计算效率并论证保护措施的合理性。

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Ecology Key Points for AQA Biology | IB AQA 生物：生态学 考点精讲