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

📚 IB WJEC Biology: Ecology Key Points | IB WJEC 生物：生态学 考点精讲

Ecology is a central topic in both IB and WJEC Biology specifications, encompassing the study of organisms and their interactions with the environment. This revision guide distils the essential concepts you need to master, from population dynamics to energy flow and nutrient cycles.

生态学是 IB 和 WJEC 生物学大纲中的核心话题，涵盖生物体及其与环境的相互作用。本考点精讲浓缩了你需要掌握的关键概念，从种群动态到能量流动和营养物质循环。

1. Populations and Population Growth | 种群与种群增长

A population is a group of organisms of the same species living in the same area at the same time. Key factors influencing population size are birth rate, death rate, immigration and emigration.

种群是指同一物种在同一时间生活在同一区域的一群生物。影响种群大小的关键因素是出生率、死亡率、迁入率和迁出率。

When resources are unlimited, a population grows exponentially. This is described by the equation dN/dt = rN, where dN/dt is the rate of population change, N is population size, and r is the intrinsic rate of increase.

当资源不受限制时，种群呈指数增长。这由方程 dN/dt = rN 描述，其中 dN/dt 为种群变化率，N 为种群大小，r 为内禀增长率。

dN/dt = rN

In nature, exponential growth cannot continue indefinitely. A more realistic model is logistic growth, which incorporates carrying capacity (K), the maximum population size that an environment can sustain.

在自然界中，指数增长不可能无限持续。更现实的模型是逻辑斯蒂增长，它包含了环境容纳量 (K)，即环境所能维持的最大种群数量。

dN/dt = rN × (K – N) / K

When N is small, growth is nearly exponential. As N approaches K, the growth rate slows to zero. Factors that regulate population size can be density-dependent (e.g. competition, predation, disease) or density-independent (e.g. natural disasters, climate extremes).

当 N 很小时，增长接近指数式。随着 N 接近 K，增长率逐渐减缓至零。调节种群大小的因素可以是密度制约的（如竞争、捕食、疾病）或非密度制约的（如自然灾害、极端气候）。

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2. r-Strategists and K-Strategists | r-对策与 K-对策

Species can be broadly categorised by their reproductive strategies. r-strategists thrive in unstable environments, producing many offspring with little parental care. K-strategists live in stable environments and invest heavily in a few offspring.

物种可根据繁殖策略大致分为两类。r-对策者在不稳定环境中繁盛，产生大量后代而极少亲代抚育。K-对策者生活在稳定环境中，对少量后代投入大量抚育。

Feature | 特征	r-strategist | r-对策者	K-strategist | K-对策者
Lifespan | 寿命	Short | 短	Long | 长
Number of offspring | 后代数量	Many | 多	Few | 少
Parental care | 亲代抚育	Little or none | 很少或无	Extensive | 广泛的
Population growth | 种群增长	Exponential, boom-bust | 指数型，繁荣-崩溃	Near K, stable | 接近 K，稳定
Examples | 实例	Bacteria, insects, weeds | 细菌、昆虫、杂草	Elephants, whales, humans | 大象、鲸、人类

Survivorship curves further illustrate these strategies: Type I (K-selected, high survival until old age), Type II (constant mortality rate), and Type III (r-selected, very high early mortality).

存活曲线进一步说明了这些策略：I 型（K-选择，直至老年才出现高死亡率），II 型（恒定死亡率），以及 III 型（r-选择，早期死亡率极高）。

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3. Community Interactions: Competition and Predation | 群落互动：竞争与捕食

Interspecific competition occurs when different species compete for the same limited resources, reducing the fitness of both. Predation involves one organism (predator) killing and eating another (prey).

种间竞争发生在不同物种为相同有限资源而竞争时，降低双方的适合度。捕食关系涉及一种生物（捕食者）杀死并吃掉另一种（猎物）。

Predator-prey cycles often show time-lagged oscillations. A classic example is the lynx and snowshoe hare, where rises in hare numbers are followed by increases in lynx numbers, leading to a crash in the hare population, then a decline in lynxes.

捕食者-猎物循环通常呈现时滞振荡。经典例子是猞猁和雪鞋兔，野兔数量上升后猞猁数量增加，导致野兔种群崩溃，接着猞猁数量下降。

Herbivory is a form of predation where animals consume plants. Symbiotic relationships include mutualism (+/+), commensalism (+/0) and parasitism (+/-). In mutualism, both species benefit, e.g. nitrogen-fixing bacteria in legume root nodules. Parasitism benefits the parasite at the host’s expense.

植食是动物消耗植物的一种捕食形式。共生关系包括互利共生 (+/+)、偏利共生 (+/0) 和寄生 (+/-)。在互利共生中，双方都受益，例如豆科植物根瘤中的固氮菌。寄生则是寄生物以牺牲宿主为代价获益。

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4. Ecological Niche and Competitive Exclusion | 生态位与竞争排斥

A species’ ecological niche is its role within the ecosystem, including its habitat, resource use and interactions. The fundamental niche is the full range of conditions a species can potentially occupy; the realised niche is the narrower set it actually uses due to biotic interactions.

一个物种的生态位是其在生态系统中的角色，包括栖息地、资源利用及相互作用。基础生态位是物种潜在可占据的全部条件范围；实际生态位则是由于生物相互作用而实际利用的更窄的部分。

The competitive exclusion principle states that two species cannot coexist indefinitely if they have identical niches. One will outcompete the other, leading to extinction or niche differentiation. Gause’s experiments with Paramecium species illustrated this.

竞争排斥原理指出，如果两个物种具有完全相同的生态位，则无法无限共存。一个物种会在竞争中胜过另一个，导致灭绝或生态位分化。高斯对草履虫种的实验证明了这一点。

Resource partitioning often evolves, where species divide a resource by using different parts (e.g. different feeding zones in a tree canopy) or being active at different times, reducing direct competition.

资源分割常常通过进化产生，物种通过利用不同部分（如树冠不同取食区域）或在不同时间活动来划分资源，从而减少直接竞争。

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

Energy enters most ecosystems as sunlight, which is captured by autotrophs (producers) via photosynthesis. Heterotrophs (consumers) obtain energy by feeding on other organisms, and decomposers break down dead organic matter, returning nutrients to the soil.

能量以阳光的形式进入大多数生态系统，由自养生物（生产者）通过光合作用捕获。异养生物（消费者）通过取食其他生物获得能量，分解者则分解死有机物质，将养分返还土壤。

Organisms are grouped into trophic levels: primary producers, primary consumers (herbivores), secondary consumers (carnivores that eat herbivores), tertiary consumers and so on. A food chain is a single linear pathway, while a food web shows interconnected feeding relationships.

生物被归入营养级：初级生产者、初级消费者（植食动物）、次级消费者（食植食动物的肉食动物）、三级消费者等。食物链是单一线性路径，而食物网展示相互关联的取食关系。

At each trophic level, energy is lost as heat through respiration, and not all biomass is consumed or assimilated. Typically, only about 10% of energy is transferred from one trophic level to the next, limiting the length of food chains.

在每一营养级，能量通过呼吸以热的形式散失，且并非所有生物质都被消耗或同化。通常只有约 10% 的能量从一营养级传递到下一级，这限制了食物链的长度。

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6. Ecological Pyramids | 生态金字塔

Ecological pyramids visually represent the structure of an ecosystem. Pyramid of numbers shows the count of organisms at each trophic level. Pyramid of biomass shows the total dry mass, and pyramid of energy illustrates the energy content.

生态金字塔直观地展示生态系统结构。数量金字塔显示各营养级的生物个体数量。生物量金字塔显示总干质量，而能量金字塔展示能量含量。

Energy pyramids are always upright because energy decreases at higher trophic levels. Pyramids of numbers and biomass can sometimes be inverted. For example, a pyramid of biomass in an aquatic ecosystem may show a small producer biomass (phytoplankton) supporting a larger consumer biomass (zooplankton) at a given moment, though over a whole year it is usually upright.

能量金字塔总是正立的，因为高营养级能量减少。数量金字塔和生物量金字塔有时会倒置。例如，在水生生态系统中，某一时刻的生物量金字塔可能显示较小的生产者生物量（浮游植物）支撑着较大的消费者生物量（浮游动物），尽管按全年来看通常是正立的。

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7. Productivity and Efficiency | 生产力与效率

Primary productivity is the rate at which producers convert light energy into chemical energy. Gross primary productivity (GPP) is the total energy fixed by photosynthesis, while net primary productivity (NPP) is the energy remaining after plant respiration (R).

初级生产力是生产者将光能转化为化学能的速率。总初级生产力 (GPP) 是光合作用固定的总能量，而净初级生产力 (NPP) 是植物呼吸作用 (R) 后剩余的能量。

NPP = GPP – R

NPP represents the energy available to the next trophic level. Secondary productivity is the rate at which consumers convert chemical energy in their food into their own biomass.

NPP 代表可供下一营养级利用的能量。次级生产力是消费者将食物中的化学能转化为自身生物量的速率。

The efficiency of energy transfer between trophic levels can be calculated. Ecological efficiency is often around 10%, but varies. Human food chains are more efficient when based on plants directly, due to reduced energy loss.

营养级之间的能量传递效率可以计算。生态效率通常在 10% 左右，但有所变化。当人类食物链直接基于植物时更高效，因为减少了能量损失。

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8. Biogeochemical Cycles: Carbon and Nitrogen | 生物地球化学循环：碳与氮

The carbon cycle involves pools in the atmosphere (CO₂), living organisms, fossil fuels and oceans. Processes include photosynthesis (CO₂ fixation), respiration (release of CO₂), decomposition, combustion and sedimentation.

碳循环涉及大气（CO₂）、生物体、化石燃料和海洋中的碳库。过程包括光合作用（固定 CO₂）、呼吸作用（释放 CO₂）、分解、燃烧和沉积作用。

Human activities, especially burning fossil fuels and deforestation, have increased atmospheric CO₂, enhancing the greenhouse effect and contributing to global climate change.

人类活动，特别是燃烧化石燃料和毁林，增加了大气 CO₂，加剧了温室效应，导致全球气候变化。

The nitrogen cycle is crucial because nitrogen is a component of proteins and nucleic acids. Key forms include atmospheric N₂, ammonium ions (NH₄⁺), nitrite ions (NO₂⁻) and nitrate ions (NO₃⁻). Nitrogen fixation converts N₂ into ammonia (NH₃) or NH₄⁺, carried out by free-living and symbiotic bacteria.

氮循环至关重要，因为氮是蛋白质和核酸的成分。关键形态包括大气 N₂、铵离子 (NH₄⁺)、亚硝酸根离子 (NO₂⁻) 和硝酸根离子 (NO₃⁻)。固氮作用将 N₂ 转化为氨 (NH₃) 或 NH₄⁺，由自由生活和共生细菌完成。

Nitrification is the oxidation of NH₄⁺ to NO₂⁻ (by Nitrosomonas) and then to NO₃⁻ (by Nitrobacter). Denitrification returns N₂ to the atmosphere under anaerobic conditions. Ammonification releases NH₄⁺ from organic nitrogen during decomposition. Excessive fertiliser use can lead to eutrophication, depleting oxygen in water bodies.

硝化作用是将 NH₄⁺ 氧化为 NO₂⁻（由亚硝酸菌属完成）然后 NO₃⁻（由硝酸菌属完成）。反硝化作用在厌氧条件下将 N₂ 送回大气。氨化作用在分解过程中从有机氮释放 NH₄⁺。过量使用化肥会导致富营养化，耗尽水体中的氧气。

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9. Succession: Primary and Secondary | 演替：初生与次生

Ecological succession is the gradual, directional change in species composition of a community over time. Primary succession begins on bare, lifeless substrate such as volcanic rock or glacial moraine. Pioneer species like lichens and mosses colonise first, breaking down rock and forming soil.

生态演替是一个群落物种组成随时间发生的渐进、方向性变化。初生演替始于裸露、无生命的基质，如火山岩或冰碛。地衣和苔藓等先锋物种首先定居，分解岩石并形成土壤。

As soil deepens, grasses, shrubs and eventually trees appear, leading to a climax community – a stable, self-perpetuating assemblage of species suited to the local climate. Secondary succession occurs in areas where soil remains after a disturbance, such as after a forest fire or abandoned farmland, proceeding faster because of the existing seed bank and soil.

随着土壤变厚，草本植物、灌木乃至乔木相继出现，最终形成顶级群落——一个适应本地气候的稳定、自我维持的物种组合。次生演替发生在扰动后土壤仍保留的区域，例如森林火灾后或废弃农田，由于已有种子库和土壤，进程更快。

Sometimes human intervention prevents succession from reaching the climatic climax, creating a plagioclimax, e.g. moorland maintained by grazing and burning.

有时人类干预阻止演替达到气候顶级，形成偏途顶级，例如通过放牧和焚烧维持的沼泽地。

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10. Biodiversity and Conservation | 生物多样性与保护

Biodiversity includes species richness (the number of different species) and evenness (the relative abundance of each species). A community with high evenness is considered more diverse. Simpson’s diversity index (D) is commonly used to quantify biodiversity.

生物多样性包括物种丰富度（不同物种的数量）和均匀度（各物种的相对丰度）。均匀度高的群落被认为多样性更高。辛普森多样性指数 (D) 常用于量化生物多样性。

D = 1 – ∑(n⁄N)²

Here n is the total number of organisms of a particular species, and N is the total number of organisms of all species. A value of D close to 1 indicates high diversity; close to 0 indicates low diversity.

这里 n 是某一物种的个体总数，N 是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。

Threats to biodiversity include habitat destruction, invasive species, overexploitation, pollution and climate change. Conservation strategies involve in-situ methods (protected areas, wildlife reserves) and ex-situ methods (botanic gardens, seed banks, captive breeding). International agreements like CITES regulate trade in endangered species.

生物多样性面临的威胁包括栖息地破坏、入侵物种、过度开发、污染和气候变化。保护策略涉及就地保护（保护区、野生动物保留地）和迁地保护（植物园、种子库、人工繁殖）。类似 CITES 的国际协议管制濒危物种贸易。

Effective conservation requires maintaining genetic diversity within populations, species diversity within communities, and ecosystem diversity across landscapes. Habitat corridors can counteract fragmentation by connecting isolated patches.

有效的保护需要维持种群内的遗传多样性、群落内的物种多样性，以及景观尺度的生态系统多样性。栖息地廊道可以通过连接孤立的斑块来抵消破碎化。

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Published by TutorHao | Biology Revision Series | aleveler.com

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