IB CIE Biology: Key Points in Ecology | IB CIE 生物：生态学考点精讲

📚 IB CIE Biology: Key Points in Ecology | IB CIE 生物：生态学考点精讲

Ecology is the branch of biology that studies the interactions among living organisms and between organisms and their physical environment. It seeks to understand the distribution and abundance of organisms, the flow of energy, and the cycling of matter through ecosystems. This revision guide consolidates the essential examination topics for both IB and CIE Biology, including ecosystem structure, energy flow, nutrient cycles, population dynamics, and human impacts.

生态学是研究生物之间以及生物与其物理环境之间相互作用的生物学分支。它致力于理解生物的分布与多度、能量流动以及物质在生态系统中的循环。这份复习指南整合了 IB 与 CIE 生物考试的核心考点，涵盖生态系统结构、能量流动、营养物质循环、种群动态及人类影响等主题。

1. Ecosystems: Definitions and Components | 生态系统：定义与组成

An ecosystem consists of all the living organisms (biotic factors) in a given area interacting with each other and with the non-living (abiotic) components such as sunlight, temperature, water, soil, and pH. The boundaries of an ecosystem may be large, like a forest, or small, like a pond.

生态系统由某一区域内所有生物（生物因素）彼此之间以及与非生物因素（如阳光、温度、水分、土壤、pH）的相互作用组成。生态系统的边界可以很大，如一片森林，也可以很小，如一个池塘。

A population is a group of individuals of the same species living in the same area at the same time and capable of interbreeding. The community refers to all the populations of different species living and interacting in an ecosystem.

种群是同一时期生活在同一区域、能够相互交配的同种生物个体的集合。群落则指生活在同一生态系统中所有不同物种种群的集合，它们彼此相互作用。

The habitat is the specific place where an organism lives, characterised by its abiotic conditions. The niche is the role of an organism in its ecosystem, encompassing all its interactions with biotic and abiotic factors, including its feeding relationships, activity patterns, and reproductive strategies. No two species can occupy exactly the same niche indefinitely (competitive exclusion principle).

栖息地是生物生活的具体地点，由非生物条件决定。生态位是生物在生态系统中的角色，涵盖它与所有生物和非生物因素的相互作用，包括摄食关系、活动模式以及繁殖策略。两个物种不能无限期占据完全相同的生态位（竞争排斥原理）。

2. Trophic Levels, Food Chains and Food Webs | 营养级、食物链与食物网

Energy flows through an ecosystem via feeding relationships. Organisms are grouped into trophic levels according to their primary energy source. Producers (autotrophs) convert light energy into chemical energy via photosynthesis. Consumers (heterotrophs) obtain energy by feeding on other organisms: primary consumers (herbivores), secondary consumers (carnivores that eat herbivores), and tertiary consumers (carnivores that eat other carnivores). Decomposers (saprotrophs) break down dead organic matter, releasing nutrients back into the soil.

能量通过摄食关系在生态系统中流动。根据主要能量来源，生物被划分为不同营养级。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）通过取食其他生物获取能量：初级消费者（食草动物）、次级消费者（以食草动物为食的食肉动物）、三级消费者（以其他食肉动物为食的食肉动物）。分解者（腐生生物）分解死亡的有机物质，将养分释放回土壤。

A food chain is a linear sequence showing the transfer of energy from one trophic level to the next, e.g. grass → rabbit → fox. A food web is a network of interconnected food chains that more accurately represents the feeding relationships in an ecosystem, as most organisms consume or are consumed by more than one species.

食物链是一条线性序列，显示能量从一个营养级传递到下一个营养级，例如：草 → 兔 → 狐狸。食物网是由相互连接的食物链组成的网络，能更真实地反映生态系统的摄食关系，因为大多数生物会取食多种生物或被多种生物取食。

3. Energy Flow and Ecological Efficiency | 能量流动与生态效率

Energy transfer between trophic levels is highly inefficient. On average, only about 10% of the energy in one trophic level is converted into new biomass in the next level. The remaining 90% is lost through metabolic heat (respiration), undigested materials (egestion), uneaten parts, and excretion (urine).

营养级之间的能量传递效率极低。平均而言，某一营养级的能量仅有约10%转化为下一营养级的新生物量。其余90%通过代谢产热（呼吸作用）、未消化物质（排遗）、未被取食的部分以及排泄（尿液）等途径散失。

Ecological efficiency can be calculated as: Energy incorporated into new biomass at trophic level n+1 divided by Energy consumed at trophic level n, expressed as a percentage. This low efficiency limits the length of food chains, typically to four or five trophic levels.

生态效率可计算为：营养级 n+1 新生物量中所含的能量除以营养级 n 摄入的能量，以百分比表示。这种低效率限制了食物链的长度，通常不超过四到五个营养级。

The gross primary production (GPP) is the total energy fixed by producers in photosynthesis. Net primary production (NPP) is the energy remaining after plant respiration: NPP = GPP − respiration. NPP represents the energy available to the next trophic level.

总初级生产量 (GPP) 是生产者通过光合作用固定的总能量。净初级生产量 (NPP) 是植物呼吸消耗后剩余的能量：NPP = GPP − 呼吸消耗。NPP 代表可供下一营养级利用的能量。

4. Ecological Pyramids | 生态金字塔

Ecological pyramids are graphical representations of trophic structure. Pyramids of numbers show the number of individuals at each trophic level, but can be inverted (e.g. one tree supports many insects). Pyramids of biomass show the total dry mass of organisms; they are usually upright but may be inverted in aquatic ecosystems where phytoplankton biomass is low but reproduces rapidly.

生态金字塔是对营养结构的图形化表示。数量金字塔显示各营养级的个体数量，但可能发生倒置（例如一棵树支撑众多昆虫）。生物量金字塔显示生物的总干重；通常呈正置形，但在浮游植物生物量低而繁殖快速的水生生态系统中也可能倒置。

Pyramids of energy depict the rate of energy flow at each trophic level over a given time. They are always upright because energy is always lost at each transfer, never increasing up the chain. Examiners often ask students to draw and interpret pyramids accurately.

能量金字塔表示给定时间内各营养级的能量流动速率。它们始终为正置形，因为能量在每次传递中总是损耗，绝不可能沿食物链向上增加。考官常要求考生精确绘制并解读这些金字塔。

5. The Carbon Cycle and Climate Change | 碳循环与气候变化

Carbon is continuously cycled between the atmosphere, organisms, oceans, and fossil fuels. Key processes include:

碳在大气、生物、海洋和化石燃料之间不断循环。主要过程包括：

Photosynthesis: producers fix CO₂ from the atmosphere into organic compounds.
光合作用：生产者将大气中的 CO₂ 固定为有机化合物。
Respiration: all organisms release CO₂ back into the atmosphere through aerobic respiration.
呼吸作用：所有生物通过有氧呼吸将 CO₂ 释放回大气。
Combustion: burning of fossil fuels and biomass releases stored carbon as CO₂.
燃烧：化石燃料和生物质燃烧将储存的碳以 CO₂ 形式释放。
Decomposition: decomposers break down dead matter, releasing CO₂ and returning nutrients to the soil.
分解作用：分解者分解死亡物质，释放 CO₂ 并将养分归还土壤。
Sedimentation and fossilisation: over millions of years, organic carbon can be converted into fossil fuels or limestone.
沉积与化石化：历经数百万年，有机碳可转化为化石燃料或石灰岩。

Increased atmospheric CO₂ from human activities enhances the greenhouse effect, leading to global warming and climate change. The melting of ice caps, rising sea levels, and extreme weather events are linked to this disruption of the carbon cycle.

人类活动导致大气 CO₂ 浓度升高，加剧温室效应，引发全球变暖和气候变化。冰盖融化、海平面上升以及极端天气事件均与碳循环的此扰动有关。

6. The Nitrogen Cycle | 氮循环

Nitrogen is essential for the synthesis of proteins and nucleic acids. Most organisms cannot use atmospheric N₂ directly; it must be converted into usable forms. The cycle involves several microbial-mediated steps:

氮是合成蛋白质和核酸的必需元素。多数生物无法直接利用大气中的 N₂，它必须转换为可被利用的形式。循环包含若干由微生物介导的步骤：

Nitrogen fixation: conversion of N₂ gas into ammonium (NH₄⁺) by free-living bacteria (e.g. Azotobacter) or symbiotic bacteria in root nodules of legumes (Rhizobium).
固氮作用：由自由生活的细菌（如固氮菌）或豆科植物根瘤中的共生细菌（根瘤菌）将 N₂ 转化为铵离子 (NH₄⁺)。
Nitrification: ammonium is oxidised to nitrite (NO₂⁻) by Nitrosomonas, then to nitrate (NO₃⁻) by Nitrobacter. This process requires oxygen.
硝化作用：铵盐被亚硝化单胞菌 (Nitrosomonas) 氧化为亚硝酸盐 (NO₂⁻)，再由硝化杆菌 (Nitrobacter) 氧化为硝酸盐 (NO₃⁻)。此过程需氧。
Assimilation: plants absorb nitrate and ammonium to build amino acids and proteins. Consumers obtain nitrogen by feeding on these plants.
同化作用：植物吸收硝酸盐和铵盐以构建氨基酸和蛋白质。消费者通过取食植物获得氮。
Ammonification: decomposers convert organic nitrogen in dead organisms and waste into ammonium, returning it to the soil.
氨化作用：分解者将死亡生物和排泄物中的有机氮转化为铵盐，归还土壤。
Denitrification: anaerobic bacteria (e.g. Pseudomonas) convert nitrate back to N₂ gas, releasing it into the atmosphere.
反硝化作用：厌氧细菌（如假单胞菌）将硝酸盐还原成 N₂ 气体，释放到大气中。

The nitrogen cycle is often a challenging topic; understanding the role of specific bacteria and the conditions required for each step is crucial for exams.

氮循环常是难点；理解特定细菌的作用以及每一步所需的条件对考试至关重要。

7. Population Growth Curves | 种群增长曲线

In an environment with unlimited resources, a population can grow exponentially. This J-shaped curve is described by the differential equation:

在资源无限的环境中，种群可呈指数增长。这种 J 型曲线可用微分方程描述：

ΔN/Δt = rN

where ΔN/Δt is the rate of population growth, N is the population size, and r is the intrinsic rate of increase.

其中 ΔN/Δt 是种群增长率，N 是种群大小，r 为内禀增长率。

In nature, resources become limiting, and populations follow a logistic (sigmoidal) growth curve, which eventually levels off at the carrying capacity (K) of the environment. The logistic equation is:

在自然界，资源会受限，种群遵循逻辑斯谛（S 型）增长曲线，最终在环境容纳量 (K) 处趋于平稳。逻辑斯谛方程为：

ΔN/Δt = rN((K − N)/K)

The phases of logistic growth are: lag phase, exponential (log) phase, deceleration phase, and stationary phase. At the stationary phase, birth rate equals death rate, and the population fluctuates around K.

逻辑斯谛增长的阶段包括：延缓期、指数（对数）期、减速期和平稳期。在平稳期，出生率等于死亡率，种群数量在 K 附近波动。

Factors regulating population size can be density-dependent (e.g. competition, predation, disease) or density-independent (e.g. natural disasters, climate extremes). Both sets shape real growth patterns.

调节种群数量的因素可分为密度制约因素（如竞争、捕食、疾病）和非密度制约因素（如自然灾害、极端气候）。两者共同塑造了真实的增长模式。

8. Interspecific and Intraspecific Interactions | 种间与种内相互作用

Organisms interact within and between species, affecting population dynamics. Intraspecific competition occurs among individuals of the same species for limited resources; it is a key driver of natural selection and regulates population size.

生物在种内和种间发生相互作用，影响种群动态。种内竞争发生在同种个体间，争夺有限资源；它是自然选择的关键驱动力，并调节种群数量。

Interspecific competition arises when different species compete for the same resources. According to the competitive exclusion principle, if two species occupy exactly the same niche, one will eventually outcompete the other. Resource partitioning reduces competition.

种间竞争指不同物种争夺相同资源。根据竞争排斥原理，若两个物种占据完全相同的生态位，其中一个终将竞争胜出。资源分割可减少竞争。

Other interactions include:

其他相互作用包括：

Predation: one organism (predator) kills and eats another (prey). Predator-prey cycles often show oscillating populations.
捕食：一个生物（捕食者）杀死并吃掉另一生物（猎物）。捕食者-猎物关系常呈现周期性振荡。
Herbivory: an animal feeds on plants, affecting plant growth and distribution.
植食作用：动物取食植物，影响植物生长和分布。
Parasitism: the parasite benefits at the expense of the host, but usually does not kill it immediately.
寄生：寄生物获益而宿主受损，但通常不会立即导致宿主死亡。
Mutualism: both species benefit (e.g. bees and flowering plants, nitrogen-fixing bacteria and legumes).
互利共生：两个物种均受益（如蜜蜂与开花植物、固氮菌与豆科植物）。
Commensalism: one species benefits and the other is unaffected (e.g. barnacles on whales).
偏利共生：一方受益，另一方不受影响（如鲸身上的藤壶）。

9. Ecological Succession | 群落演替

Ecological succession is the directional change in the species composition of a community over time. Primary succession begins on bare, lifeless surfaces such as volcanic rock or sand dunes. Pioneer species like lichens and mosses colonise first, weathering the rock and forming soil. Over time, larger plants such as grasses, shrubs, and eventually trees establish, leading to a climax community.

生态演替是群落物种组成随时间发生的定向变化。原生演替始于裸露无生命的表面，如火山岩或沙丘。地衣和苔藓等先锋物种率先定殖，风化岩石并形成土壤。随时间推移，草本、灌木乃至树木相继建立，最终形成顶极群落。

Secondary succession occurs in areas where an existing community has been disturbed but soil remains (e.g. after a fire or farming). It is generally faster because the soil already contains seeds and nutrients. During succession, species diversity increases, biomass accumulates, and the environment becomes more stable.

次生演替发生在原有群落遭到干扰但土壤仍然保留的区域（如火灾或耕作后）。由于土壤中已存有种子和养分，演替通常更快。演替过程中，物种多样性增加，生物量积累，环境变得更稳定。

Climax communities are relatively stable and support a complex food web. However, continuous disturbances such as grazing, fire, or human activity can maintain a plagioclimax, preventing the development of the theoretical climax.

顶极群落相对稳定，支撑复杂的食物网。然而，持续的干扰（如放牧、火或人类活动）可维持偏途顶极，阻止理论顶极的发育。

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

Biodiversity encompasses genetic diversity (variation within a species), species diversity (number of species and their relative abundance), and ecosystem diversity (variety of habitats). High biodiversity enhances ecosystem stability, resilience, and productivity.

生物多样性包括遗传多样性（物种内变异）、物种多样性（物种数目及其相对多度）以及生态系统多样性（栖息地的多样性）。高生物多样性增强生态系统的稳定性、恢复力和生产力。

Simpson’s Diversity Index (D) is used to quantify species diversity:

D = 1 − (Σ n(n−1) / N(N−1))

where n is the number of individuals of a particular species, and N is the total number of individuals. Values closer to 1 indicate high diversity.

其中 n 为某一特定物种的个体数，N 为总个体数。值越接近 1 表示多样性越高。

Conservation strategies include in situ conservation (protecting species in their natural habitat, e.g. nature reserves) and ex situ conservation (protecting species outside their habitat, e.g. seed banks, zoos). CITES and other international agreements regulate trade in endangered species.

保护策略包括就地保护（在自然栖息地保护物种，如自然保护区）和迁地保护（在栖息地外保护物种，如种子库、动物园）。CITES 等国际协议管制濒危物种的贸易。

11. Human Impacts on Ecosystems | 人类活动对生态系统的影响

Human activities profoundly alter ecosystems. Deforestation reduces carbon sequestration, destroys habitats, and disrupts the water cycle. Intensive agriculture leads to soil degradation, eutrophication from fertiliser runoff, and loss of hedgerows and biodiversity.

人类活动深刻地改变着生态系统。森林砍伐减少碳封存、破坏栖息地并扰乱水循环。集约农业导致土壤退化、化肥径流引发的富营养化，以及树篱和生物多样性的丧失。

Pollution includes air pollution (SO₂ causing acid rain), water pollution (sewage, chemicals), and plastic pollution harming marine life. Overfishing depletes fish stocks and disrupts marine food webs.

污染包括空气污染（SO₂ 导致酸雨）、水污染（污水、化学品）以及危害海洋生物的塑料污染。过度捕捞耗尽鱼类资源并破坏海洋食物网。

Introducing alien species can cause native species to decline by competition, predation, or disease. Climate change, driven by greenhouse gas emissions, leads to rising temperatures, shifting species distributions, and phenological mismatches. Sustainable practices such as reforestation, integrated pest management, and renewable energy use are critical to mitigating these impacts.

引入外来物种可通过竞争、捕食或疾病导致本地物种衰退。温室气体排放驱动的气候变化导致气温上升、物种分布迁移及物候错配。植树造林、综合虫害管理和可再生能源使用等可持续实践对缓解这些影响至关重要。

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IB CIE Biology: Key Points in Ecology | IB CIE 生物：生态学考点精讲