📚 IB OCR Biology: Ecology Key Points | IB OCR 生物：生态学考点精讲
Ecology is the scientific study of how organisms interact with each other and with their physical environment. It provides critical insights into the functioning of ecosystems, biodiversity maintenance, and the impacts of human activities. Mastering ecology is essential for both IB and OCR A-level Biology exams.
生态学是研究生物体之间以及与其物理环境如何相互作用的科学。它为生态系统的运作、生物多样性的维持以及人类活动的影响提供了关键见解。掌握生态学是IB和OCR A-level生物学考试的重点。
1. What is Ecology? | 什么是生态学？
Ecology examines the relationships between living organisms (biotic components) and their non-living surroundings (abiotic components). It can be studied at various hierarchical levels: organism, population, community, ecosystem, and biosphere. An organism is a single living individual; a population is a group of individuals of the same species living in a specific area; a community includes all populations of different species interacting in an area; an ecosystem encompasses the community and its abiotic environment; the biosphere is the global sum of all ecosystems.
生态学研究生物（生物成分）与其非生物环境（非生物成分）之间的关系。它可以在不同层次上进行研究：个体、种群、群落、生态系统和生物圈。个体是单个生物；种群是生活在特定区域的同一物种个体群；群落包括一个区域内相互作用的全部不同物种种群；生态系统包含群落及其非生物环境；生物圈是所有生态系统的全球总和。
2. Abiotic and Biotic Factors | 非生物因素与生物因素
Abiotic factors are non-living physical and chemical conditions such as temperature, light, water, pH, and soil minerals. Biotic factors are living components including competition, predation, and disease. Both types of factors determine the distribution and abundance of organisms. For example, plant growth is limited by water availability (abiotic) and herbivory (biotic).
非生物因素是非生物理化条件，如温度、光照、水分、pH和土壤矿物质。生物因素是生物成分，包括竞争、捕食和疾病。两类因素共同决定生物的分布和数量。例如，植物生长受水分可用性（非生物）和食草动物（生物）的限制。
3. Populations and Carrying Capacity | 种群与承载量
A population is defined by its size, density, and distribution. Population growth is influenced by birth rate, death rate, immigration, and emigration. The carrying capacity (K) is the maximum population size that an environment can sustain indefinitely. When resources become limiting, growth slows and stabilizes around K, producing an S-shaped (sigmoid) logistic curve. In contrast, exponential growth occurs only temporarily when resources are abundant.
种群由其大小、密度和分布定义。种群增长受出生率、死亡率、迁入和迁出的影响。承载量（K）是环境能持续维持的最大种群规模。当资源成为限制因素时，增长减缓并稳定在K附近，形成S型（逻辑斯谛）曲线。相反，指数增长仅在资源丰富时暂时出现。
4. Community Interactions: Competition, Predation, Symbiosis | 群落相互作用：竞争、捕食、共生
Species interact in several ways: competition (-/-) where both species suffer due to shared limited resources; predation (+/-) where one benefits and the other is harmed; herbivory; and symbiosis, which includes mutualism (+/+), commensalism (+/0), and parasitism (+/-). The competitive exclusion principle states that two species competing for the exact same resources cannot coexist indefinitely – one will outcompete the other. Resource partitioning allows coexistence.
物种之间存在多种相互作用：竞争（-/-），即双方因争夺有限资源而受损；捕食（+/-），一方受益一方受害；食草；以及共生，包括互利共生（+/+）、偏利共生（+/0）和寄生（+/-）。竞争排斥原理指出，两个竞争完全相同资源的物种无法无限期共存——一方会战胜另一方。资源分割使共存成为可能。
5. Energy Flow in Ecosystems | 生态系统中的能量流动
The sun is the primary source of energy for most ecosystems. Producers (autotrophs) convert light energy into chemical energy via photosynthesis. Consumers (heterotrophs) obtain energy by feeding on other organisms. Decomposers break down dead organic matter, recycling nutrients. Energy flows through an ecosystem in a one-way direction and is lost as heat at each trophic level due to respiration, excretion, and incomplete digestion. On average, only about 10% of energy is transferred from one trophic level to the next.
太阳是大多数生态系统的主要能源。生产者（自养生物）通过光合作用将光能转化为化学能。消费者（异养生物）通过摄食其他生物获取能量。分解者分解死亡的有机物，循环养分。能量在生态系统中单向流动，并在每个营养级通过呼吸、排泄和不完全消化以热的形式散失。平均而言，只有约10%的能量从一个营养级传递到下一个营养级。
6. Food Chains, Food Webs, and Trophic Levels | 食物链、食物网与营养级
A food chain illustrates a single linear pathway of energy transfer, e.g., grass → rabbit → fox. A food web is a more realistic representation of interconnected food chains. Trophic levels include producers (1st trophic level), primary consumers (2nd), secondary consumers (3rd), tertiary consumers (4th), and so on. Organisms that feed at multiple trophic levels are omnivores.
食物链展示能量传递的单一线性路径，例如草 → 兔 → 狐狸。食物网是相互连接的食物链的更真实表示。营养级包括生产者（第一营养级）、初级消费者（第二）、次级消费者（第三）、三级消费者（第四）等。以多个营养级为食的生物是杂食动物。
7. Ecological Pyramids | 生态金字塔
Ecological pyramids provide a graphical representation of the relationship between organisms at different trophic levels. The pyramid of numbers shows the count of individuals; the pyramid of biomass shows the total dry mass; and the pyramid of energy shows the energy content, which is always upright because energy decreases at higher levels. Some pyramids of numbers or biomass can be inverted (e.g., a single tree supporting many insects).
生态金字塔用图形表示不同营养级生物之间的关系。数量金字塔显示个体数量；生物量金字塔显示总干重；能量金字塔显示能量含量，它总是直立的，因为能量随营养级升高而减少。有些数量金字塔或生物量金字塔可以是倒置的（例如一棵树支持许多昆虫）。
8. Nutrient Cycles: Carbon and Nitrogen | 养分循环：碳循环与氮循环
Carbon cycle: Carbon dioxide (CO₂) in the atmosphere is fixed by photosynthesis into organic compounds. It returns via respiration, decomposition, and combustion of fossil fuels. Oceans act as a carbon sink. Nitrogen cycle: Atmospheric N₂ is fixed by nitrogen-fixing bacteria (e.g., Rhizobium) into ammonia (NH₃) or ammonium (NH₄⁺). Nitrification by nitrifying bacteria converts NH₄⁺ to nitrites (NO₂⁻) then to nitrates (NO₃⁻). Plants absorb nitrates and assimilate nitrogen into proteins. Decomposers perform ammonification. Denitrifying bacteria convert nitrates back to N₂ gas, completing the cycle.
碳循环：大气中的二氧化碳（CO₂）通过光合作用被固定为有机物。它通过呼吸作用、分解和化石燃料的燃烧返回。海洋是碳汇。氮循环：大气中的N₂被固氮细菌（如根瘤菌）固定为氨（NH₃）或铵（NH₄⁺）。硝化细菌通过硝化作用将NH₄⁺转化为亚硝酸盐（NO₂⁻）再转化为硝酸盐（NO₃⁻）。植物吸收硝酸盐，将氮同化为蛋白质。分解者进行氨化作用。反硝化细菌将硝酸盐还原为N₂气体，完成循环。
9. Population Growth Models: Exponential vs. Logistic | 种群增长模型：指数增长与逻辑斯谛增长
Exponential growth is described by the equation dN/dt = rN, where r is the intrinsic rate of increase. It yields a J-shaped curve and occurs in ideal conditions. Logistic growth incorporates environmental resistance with the equation dN/dt = rN (1 – N/K). As N approaches K, growth rate approaches zero. This produces a sigmoid curve. Density-dependent factors (disease, competition) regulate populations; density-independent factors (fires, storms) affect them regardless of size.
指数增长由方程 dN/dt = rN 描述，r 为内禀增长率。它形成J型曲线，发生在理想条件下。逻辑斯谛增长纳入环境阻力，方程为 dN/dt = rN (1 – N/K)。当N接近K时，增长率趋于零，产生S型曲线。密度制约因素（疾病、竞争）调节种群；非密度制约因素（火灾、风暴）无论规模大小均产生影响。
dN/dt = rN and dN/dt = rN (1 – N/K)
10. Ecological Succession | 生态演替
Ecological succession is the gradual change in species composition in an area over time. Primary succession occurs on bare, lifeless substrate (e.g., lava flow) with no soil; pioneer species like lichens and mosses colonize first, forming soil. Secondary succession occurs on disturbed soil that still contains seeds and organic matter (e.g., after a forest fire), and is generally faster. Succession leads to a climax community that is relatively stable and in equilibrium with the prevailing climate.
生态演替是物种组成在一段时间内逐渐变化的过程。原生演替发生在裸露无生命的基质（例如熔岩流）上，没有土壤；先锋物种如地衣和苔藓首先定居，形成土壤。次生演替发生在仍含有种子和有机物的受干扰土壤上（如森林火灾后），通常速度更快。演替最终形成与盛行气候平衡的相对稳定的顶极群落。
11. Biodiversity and Conservation | 生物多样性与保护
Biodiversity includes species diversity, genetic diversity, and ecosystem diversity. Species richness is the number of different species; evenness measures the relative abundance. Simpson’s Index of Diversity (D) is used to quantify diversity and is calculated as D = 1 – Σ (n/N)², where n is the number of individuals of a particular species and N is the total number of individuals. A high D indicates high diversity. Conservation efforts can be in-situ (within natural habitats, e.g., national parks) or ex-situ (outside habitats, e.g., seed banks, zoos). Biodiversity is threatened by habitat loss, invasive species, pollution, overexploitation, and climate change.
生物多样性包括物种多样性、遗传多样性和生态系统多样性。物种丰富度是不同物种的数量；均匀度衡量相对丰度。辛普森多样性指数（D）用于量化多样性，计算公式为 D = 1 – Σ (n/N)²，其中 n 是特定物种的个体数，N 是个体总数。高D值表示高多样性。保护措施可以是就地保护（在自然栖息地内，如国家公园）或迁地保护（栖息地之外，如种子库、动物园）。生物多样性受到栖息地丧失、入侵物种、污染、过度开发和气候变化的威胁。
D = 1 – Σ (n/N)²
12. Human Impact on Ecosystems | 人类对生态系统的影响
Humans alter ecosystems through deforestation, agriculture, urbanization, pollution, and introduction of non-native species. Eutrophication occurs when excess nitrates and phosphates from fertilizers run off into water bodies, causing algal blooms that deplete oxygen levels. Global warming, driven by greenhouse gas emissions, affects species distribution and ecosystem functioning. Sustainable management and conservation strategies are essential to mitigate these impacts and preserve ecological balance.
人类通过砍伐森林、农业、城市化、污染和引入外来物种改变生态系统。富营养化发生在过量硝酸盐和磷酸盐从肥料流入水体时，导致藻类大量繁殖，消耗氧气。由温室气体排放驱动的全球变暖影响物种分布和生态系统功能。可持续管理和保护策略对于减轻这些影响和维护生态平衡至关重要。
Published by TutorHao | Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导