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

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

Ecology is a central topic in IB Biology, covering interactions from individuals to the biosphere. Understanding energy flow, nutrient cycling, population dynamics, and community structure is essential for exams and for appreciating environmental issues.

生态学是IB生物学的核心主题，涵盖从个体到生物圈的相互作用。理解能量流动、物质循环、种群动态和群落结构对于考试和理解环境问题至关重要。

1. What is Ecology? | 什么是生态学？

Ecology is the scientific study of how organisms interact with one another and with their physical environment. It explains the distribution and abundance of organisms, as well as the structure and function of ecosystems.

生态学是研究生物彼此之间以及与其物理环境相互作用的科学。它解释生物的分布与数量，以及生态系统的结构和功能。

Key terms include species, population, community, ecosystem, biome, and biosphere. A species is a group of organisms that can interbreed to produce fertile offspring. A population is a group of individuals of the same species living in a particular area.

关键术语包括物种、种群、群落、生态系统、生物群落和生物圈。物种是一群能够相互交配并产生能育后代的生物。种群是生活在特定区域的同种个体的集合。

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2. Ecological Hierarchy: From Organism to Biosphere | 生态学层次：从个体到生物圈

Ecological organization follows a hierarchy: organism → population → community → ecosystem → biome → biosphere. A community consists of all interacting populations in an area. An ecosystem includes the community plus the abiotic factors such as soil, water, and climate. Biomes are large regions with characteristic climate and organism types.

生态组织遵循层次：个体 → 种群 → 群落 → 生态系统 → 生物群落 → 生物圈。群落包括一个区域内所有相互作用的种群。生态系统包括群落加上土壤、水和气候等非生物因素。生物群落是具有典型气候和生物类型的大区域。

Abiotic factors (temperature, light, pH, salinity, nutrients) influence where organisms can live. Ecologists measure these factors to understand organismal distribution.

非生物因素（温度、光照、pH、盐度、养分）影响生物的栖息。生态学家测量这些因素以了解生物的分布。

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3. Trophic Levels and Food Chains/Webs | 营养级与食物链/网

Organisms are grouped into trophic levels based on their source of energy. Producers (autotrophs) convert light energy into chemical energy through photosynthesis. Primary consumers (herbivores) eat producers. Secondary and tertiary consumers are carnivores that eat other consumers. Decomposers (bacteria, fungi) break down dead organic matter, recycling nutrients.

生物根据能量来源分为营养级。生产者（自养生物）通过光合作用将光能转化为化学能。初级消费者（食草动物）吃生产者。次级和三级消费者是以其他消费者为食的食肉动物。分解者（细菌、真菌）分解死有机物，循环利用养分。

A food chain shows a single linear pathway of energy transfer, while a food web consists of many interconnected food chains, giving a more realistic picture of feeding relationships.

食物链显示能量传递的单一路路径，而食物网由许多相互连接的食物链组成，更真实地展现捕食关系。

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4. Energy Flow and Ecological Pyramids | 能量流动与生态金字塔

Energy enters ecosystems as sunlight and flows in one direction. At each trophic level, energy is lost as heat through respiration, excretion, and uneaten parts. Generally, only about 10% of the energy is transferred to the next level. This limits the length of food chains (usually no more than 4–5 trophic levels).

能量以阳光形式进入生态系统并单向流动。在每一营养级，能量通过呼吸、排泄和未被取食部分以热的形式散失。通常只有约10%的能量传递到下一营养级，这限制了食物链的长度（通常不超过4-5个营养级）。

Ecological pyramids represent trophic structure: pyramids of numbers, biomass, and energy. A pyramid of energy is always upright because energy decreases at higher levels. Pyramids of numbers and biomass may be inverted in some cases (e.g., a single tree supporting many insects).

生态金字塔表示营养结构：数量金字塔、生物量金字塔和能量金字塔。能量金字塔总是正立的，因为高营养级的能量减少。数量金字塔和生物量金字塔在某些情况下可能倒置（例如，一棵树支持许多昆虫）。

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5. Nutrient Cycles: Carbon and Nitrogen Cycles | 物质循环：碳循环与氮循环

Nutrients are recycled within and between ecosystems. The carbon cycle involves the movement of carbon among the atmosphere, organisms, oceans, and sediments. CO₂ is fixed by photosynthesis, released by respiration, decomposition, and combustion of fossil fuels. Oceans act as a large carbon sink.

养分在生态系统内及之间循环。碳循环涉及碳在大气、生物、海洋和沉积物之间的移动。CO₂通过光合作用固定，通过呼吸、分解和化石燃料燃烧释放。海洋是一个巨大的碳库。

The nitrogen cycle includes several microbial processes: nitrogen fixation (N₂ → NH₃ / NH₄⁺) by free-living bacteria (e.g., Azotobacter) or symbiotic bacteria (Rhizobium in root nodules). Nitrification: NH₄⁺ → NO₂⁻ → NO₃⁻ by nitrifying bacteria. Assimilation: plants absorb NO₃⁻ (and NH₄⁺) to make proteins. Ammonification: decomposers convert organic nitrogen into NH₄⁺. Denitrification: NO₃⁻ → N₂ by denitrifying bacteria, returning nitrogen to the atmosphere.

氮循环包括多个微生物过程：固氮作用（N₂ → NH₃ / NH₄⁺）由自由生活的细菌（如固氮菌）或共生细菌（根瘤菌在根瘤中）完成。硝化作用：NH₄⁺ → NO₂⁻ → NO₃⁻ 由硝化细菌完成。同化作用：植物吸收 NO₃⁻（和 NH₄⁺）以制造蛋白质。氨化作用：分解者将有机氮转化为 NH₄⁺。反硝化作用：NO₃⁻ → N₂ 由反硝化细菌完成，将氮返还大气。

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6. Population Growth: Exponential vs Logistic | 种群增长：指数增长与逻辑斯蒂增长

Populations can grow exponentially (J-shaped curve) when resources are unlimited and there are no limiting factors. The growth rate is proportional to the current population size: dN/dt = rN, where r is the intrinsic rate of increase. However, exponential growth is unsustainable in nature.

当资源无限且没有限制因素时，种群可呈指数增长（J形曲线）。增长率与当前种群大小成正比：dN/dt = rN，其中 r 为内禀增长率。然而，自然界中指数增长不可持续。

Logistic growth (S-shaped curve) occurs when environmental resistance slows growth as the population approaches the carrying capacity (K) of the environment: dN/dt = rN(1 – N/K). Factors such as food shortage, disease, and predation increase mortality and decrease birth rates, creating a dynamic equilibrium around K.

逻辑斯蒂增长（S形曲线）在种群接近环境容纳量（K）时环境阻力减缓增长：dN/dt = rN(1 – N/K)。食物短缺、疾病和捕食等因素增加死亡率并降低出生率，在 K 附近形成动态平衡。

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7. Species Interactions and Community Structure | 物种间关系与群落结构

Interactions between species affect population sizes and community composition. Predation (+/–): one organism benefits while the other is harmed. Competition (–/–): both species suffer when competing for limited resources (interspecific competition) or within the same species (intraspecific). Mutualism (+/+): both species benefit (e.g., pollinators and flowers). Commensalism (+/0): one benefits, the other is unaffected. Parasitism (+/–): the parasite benefits at the host’s expense.

物种间的相互作用影响种群大小和群落组成。捕食（+/–）：一方受益，另一方受害。竞争（–/–）：两种物种争夺有限资源（种间竞争）或同种个体间竞争（种内竞争）时双方受损。互利共生（+/+）：双方受益（例如传粉者与花朵）。偏利共生（+/0）：一方受益，另一方不受影响。寄生（+/–）：寄生物受益，宿主受害。

Keystone species exert a disproportionate effect on community structure relative to their abundance. Their removal can cause a trophic cascade and loss of biodiversity.

关键物种相对于其数量对群落结构产生不成比例的影响。它们被移除会引发营养级联效应和生物多样性丧失。

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8. Ecological Succession | 生态演替

Succession is the predictable change in species composition over time in a given area. Primary succession begins on bare, lifeless surfaces such as lava flows or bare rock

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