📚 A-Level Edexcel Biology: Ecology Revision Notes | 生态学考点精讲
Ecology is the branch of biology that studies the interactions between organisms and their biotic and abiotic environment. The Edexcel A-Level Biology specification requires you to understand key ecological concepts, from population dynamics and energy flow to nutrient cycles and conservation. Mastering practical techniques such as sampling and the use of statistical indices is equally vital. This revision guide distils the essential content into clear, bilingual explanations to help you tackle exam questions with confidence.
生态学是研究生物与其生物和非生物环境之间相互作用的生物学分支。Edexcel A-Level 生物考纲要求你掌握关键生态概念，从种群动态、能量流动到营养物循环和保护。同样重要的是熟练掌握采样技术和统计指数的使用。这份考点精讲将核心内容提炼成清晰的双语解析，帮助你自信应对考题。
1. Key Ecological Terms | 生态学关键词
A population is a group of individuals of the same species living in a specific area at the same time, capable of interbreeding.
种群是指同一时间生活在某一特定区域内的同种所有个体，能够相互交配。
A community consists of all the populations of different species that inhabit a shared habitat and interact with one another.
群落由共享同一栖息地并相互作用的各种不同物种种群构成。
An ecosystem encompasses the community and its abiotic environment, functioning as a dynamic system through energy flow and nutrient cycling.
生态系统包含群落及其非生物环境，通过能量流动和营养物循环作为一个动态系统运转。
A niche describes the role of a species within its ecosystem, including its habitat, feeding relationships and interactions with other organisms. The competitive exclusion principle states that two species cannot occupy the exact same niche indefinitely.
生态位描述一个物种在其生态系统中的角色，包括它的栖息地、摄食关系以及与其他生物的相互作用。竞争排斥原理指出，两个物种不可能无限期地占据完全相同的生态位。
2. Sampling Techniques | 采样技术
Random sampling is used to avoid bias when estimating species distribution or abundance in a uniform habitat. Quadrats are placed using randomly generated coordinates, and the abundance of each species is recorded.
随机采样用于在均匀生境中估计物种分布或多度时避免偏差。样方按照随机生成的坐标放置，并记录每个物种的多度。
Systematic sampling is employed where an environmental gradient exists, such as across a sand dune or a rocky shore. A line transect or belt transect is laid out, and data are collected at regular intervals along the line.
当存在环境梯度时（如沙丘或岩质海岸），采用系统采样。布设一条样线或样带，并沿线每隔一定距离收集数据。
A quadrat is typically a square frame, often 0.5 m × 0.5 m or 1 m × 1 m. For plants or slow-moving animals, percentage cover or direct counts are recorded. Replicates are essential to ensure reliability.
样方通常是一个方形框架，常见尺寸为 0.5 m × 0.5 m 或 1 m × 1 m。对植物或移动缓慢的动物，记录覆盖百分比或直接计数。重复样方是确保可靠性的关键。
3. Estimating Population Size Using Capture-Mark-Recapture | 标志重捕法估算种群数量
For mobile animals, the Lincoln index (capture-mark-recapture) estimates population size (N). A sample is captured, marked and released. After reintegration, a second sample is captured, and the number of marked individuals is recorded.
对于活动性强的动物，林肯指数（标志重捕法）用于估算种群数量（N）。先捕获一组个体，标记后放回。待重新混合后，再次捕获一组样本并记录其中带标记的个体数。
N = (M × C) / R
M = number marked in first capture; C = total number in second capture; R = number of marked recaptures. This method assumes a closed population, that marks are not lost, and that marking does not affect survival or catchability.
M = 首次捕获并标记的数量；C = 第二次捕获的总数；R = 第二次捕获中带标记的数量。该方法假设种群封闭、标记不会丢失且标记不影响生存或可捕性。
4. Ecological Succession | 生态演替
Primary succession begins on bare, lifeless surfaces such as lava flows or bare rock. Pioneer species like lichens and mosses colonise first, weathering the rock to form a thin soil. Over time, grasses, shrubs and finally trees establish, forming a climax community.
原生演替始于裸露无生命的表面，如熔岩流或裸岩。先锋物种（如地衣和苔藓）首先定殖，风化岩石形成薄薄的土壤。随时间推移，草本、灌木直至乔木立足，形成顶极群落。
Secondary succession occurs where an existing community has been cleared but soil remains, for example after a forest fire. Recovery is generally faster than primary succession.
次生演替发生在原有群落被清除但土壤保留的区域，例如森林火灾之后。恢复速度通常比原生演替更快。
Deflected succession refers to a climax community that is prevented from developing naturally due to persistent human intervention, such as mowing, grazing or controlled burning. The final community is a plagioclimax, different from the natural climax.
偏途演替指由于持续的人为干预（如割草、放牧或控制火烧），顶极群落无法自然发育。最终形成的群落为偏途顶极，与自然顶极不同。
5. Energy Flow and Productivity | 能量流动与生产力
Energy enters ecosystems through photosynthesis. Gross primary production (GPP) is the total light energy absorbed by producers and converted to chemical energy. Net primary production (NPP) is the energy remaining in plant biomass after respiratory losses (R).
能量通过光合作用进入生态系统。总初级生产力（GPP）是生产者吸收并转化为化学能的总光能。净初级生产力（NPP）是扣除呼吸损耗（R）后留在植物生物量中的能量。
NPP = GPP − R
Only a small percentage of the energy at one trophic level (approximately 10%) is transferred to the next. The rest is lost through respiration, excretion, uneaten parts and heat. This limits the length of food chains.
从一个营养级传递到下一营养级的能量通常只有约10%。其余能量以呼吸、排泄、未被取食的部分和热量形式散失。这限制了食物链的长度。
6. Ecological Pyramids | 生态金字塔
Pyramids of number represent the count of organisms at each trophic level. They can be inverted, for example when numerous small herbivores feed on one large tree.
数量金字塔表示各营养级的生物数量。它们可能是倒置的，例如大量小型植食动物取食一棵大树。
Pyramids of biomass show the total dry mass of organisms at each level. They are rarely inverted, though some aquatic ecosystems can show an inverted pyramid during a seasonal bloom. Biomass is measured in g m⁻² (or kg m⁻²).
生物量金字塔显示每一营养级生物的总干重。它很少倒置，尽管某些水生生态系在季节性水华期间可能出现倒金字塔。生物量用 g m⁻² 或 kg m⁻² 计量。
Pyramids of energy display the total energy present at each trophic level over a given time period (kJ m⁻² yr⁻¹). They are never inverted because energy transfer is always accompanied by losses. This makes energy pyramids the most accurate representation of ecosystem structure.
能量金字塔表示给定时间段内各营养级所含的总能量（kJ m⁻² yr⁻¹）。它永不会倒置，因为能量传递始终伴随损耗。这使能量金字塔成为生态系统结构最精确的表征。
7. Nutrient Cycles: Carbon and Nitrogen | 营养物循环：碳和氮
The carbon cycle involves photosynthesis, respiration, decomposition, combustion and feeding. CO₂ is fixed by plants, passed along food chains, returned to the atmosphere by respiration, and released from fossil fuel combustion. Carbonate rocks and oceans act as long-term stores.
碳循环涉及光合作用、呼吸作用、分解作用、燃烧和摄食。CO₂ 被植物固定，沿食物链传递，通过呼吸返回大气，并由化石燃料燃烧释放。碳酸盐岩石和海洋作为长期碳库。
In the nitrogen cycle, nitrogen gas (N₂) is converted to ammonia (NH₃) or ammonium ions (NH₄⁺) by nitrogen-fixing bacteria, either free-living in soil or symbiotic in root nodules of legumes. Nitrifying bacteria then oxidise ammonium to nitrites (NO₂⁻) and then to nitrates (NO₃⁻) in a process called nitrification.
在氮循环中，氮气（N₂）被固氮细菌转化为氨（NH₃）或铵离子（NH₄⁺），这些细菌可自由生活在土壤中或与豆科植物根瘤共生。随后硝化细菌将铵氧化为亚硝酸盐（NO₂⁻）再氧化为硝酸盐（NO₃⁻），这一过程称为硝化作用。
Plants absorb nitrates and assimilate them into proteins and nucleic acids. Decomposers and ammonifying bacteria release ammonium from dead organisms and waste. Denitrifying bacteria convert nitrates back to atmospheric N₂ under anaerobic conditions, completing the cycle.
植物吸收硝酸盐并将其同化为蛋白质和核酸。分解者和氨化细菌从尸体和废物中释放铵离子。反硝化细菌在厌氧条件下将硝酸盐还原为大气 N₂，完成循环。
8. Population Dynamics and Predator-Prey Relationships | 种群动态与捕食关系
Predator and prey population sizes show cyclic fluctuations. An increase in prey leads to increased predator numbers after a time lag. High predation pressure reduces prey numbers, which subsequently causes the predator population to decline due to food shortage.
捕食者与猎物种群数量呈现周期性波动。猎物增多导致捕食者在经历时间滞后之后数量增加。较高的捕食压力使猎物数量下降，随后捕食者因食物短缺而数量减少。
Competition can be interspecific (between species) or intraspecific (within a species). Intraspecific competition is often a major driver of natural selection, as individuals compete for limited resources such as food, territory and mates.
竞争可以是种间的或种内的。种内竞争通常是自然选择的主要驱动力，因为个体间为食物、领域和配偶等有限资源而竞争。
Carrying capacity is the maximum population size that an environment can sustain indefinitely. Limiting factors include food supply, space, disease and accumulation of wastes.
环境容纳量是指环境能够持续支撑的最大种群规模。限制因素包括食物供应、空间、疾病和废物积累。
9. Biodiversity and Simpson’s Index | 生物多样性与辛普森指数
Species richness is simply the number of different species in a habitat. However, it does not account for the relative abundance of each species. Simpson’s Index of Diversity (D) combines species richness and evenness into one value between 0 and 1.
物种丰富度仅仅是一个生境中不同物种的数量。但它不考虑各物种的相对多度。辛普森多样性指数（D）将物种丰富度和均匀度结合为一个 0 到 1 之间的数值。
D = 1 − Σ (n / N)²
n = total number of individuals of a particular species; N = total number of all individuals across all species. A higher D value indicates greater biodiversity. The index is particularly useful for comparing different habitats or monitoring changes over time.
n = 某一特定物种的个体总数；N = 所有物种的个体总数。D 值越高表示生物多样性越高。该指数对于比较不同生境或监测随时间的变化尤其有用。
10. Human Impacts and Conservation | 人类影响与保护
Eutrophication occurs when excess nitrates and phosphates from fertilisers, sewage or detergents enter water bodies. This causes algal blooms that block light, killing aquatic plants. As decomposers break down the dead organic matter, oxygen is consumed, creating hypoxic zones where many organisms cannot survive.
富营养化发生在过量来自化肥、污水或洗涤剂的硝酸盐和磷酸盐进入水体时。这导致藻类水华，遮蔽光线，杀死水生植物。分解者分解死亡有机质时耗氧，形成缺氧区，许多生物无法生存。
Global warming is accelerated by increased greenhouse gas emissions (CO₂, methane, CH₄). This leads to rising sea levels, shifts in species distributions and more frequent extreme weather events. Deforestation exacerbates the problem by reducing carbon sequestration and destroying habitats.
全球变暖因温室气体排放（CO₂、甲烷）增加而加剧。这导致海平面上升、物种分布偏移以及更频繁的极端天气事件。森林砍伐通过减少碳汇和破坏栖息地使问题恶化。
Conservation strategies include in situ protection (e.g. national parks, marine reserves), ex situ measures (e.g. seed banks, captive breeding) and habitat restoration. Legislation and international agreements also play crucial roles in preserving biodiversity for future generations.
保护策略包括就地保护（如国家公园、海洋保护区）、迁地措施（如种子库、人工繁殖）以及栖息地恢复。立法和国际协定在为后代保存生物多样性方面也发挥着关键作用。
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