CIE A-Level Biology: Levels of Biodiversity | CIE A-Level 生物：生物多样性的层次

📚 CIE A-Level Biology: Levels of Biodiversity | CIE A-Level 生物：生物多样性的层次

Biodiversity, short for biological diversity, refers to the variety of life on Earth at all its levels, from genes to entire ecosystems. In the CIE A-Level Biology syllabus, understanding the levels of biodiversity is fundamental to appreciating ecological relationships, evolution, and conservation biology. This article systematically unpacks these levels as required by the Cambridge International examination framework.

生物多样性，即生物学多样性的简称，是指地球上从基因到整个生态系统所有层次的生命变异。在 CIE A-Level 生物考纲中，理解生物多样性的层次是掌握生态关系、进化与保护生物学的基石。本文将按照剑桥国际考试要求，系统地解析这些层次。

1. Defining Biodiversity | 生物多样性的定义

Biodiversity encompasses the variety and variability among living organisms and the ecological complexes in which they occur. It includes diversity within species, between species, and of ecosystems. The term was coined by Walter Rosen in 1985 and popularised by E.O. Wilson, but the concept now forms a cornerstone of modern ecology and conservation science.

生物多样性涵盖生物有机体之间及其所存在的生态复合体中的差异与可变性。它包括物种内部的多样性、物种之间的多样性以及生态系统的多样性。该术语由沃尔特·罗森于1985年提出，并经E.O.威尔逊推广，但这一概念如今已成为现代生态学与保护科学的基石。

For A-Level purposes, you must distinguish three principal levels: genetic diversity, species diversity, and ecosystem (habitat) diversity. Each level provides a different lens for measuring and interpreting the richness of life, and each demands different conservation strategies.

就 A-Level 考试而言，必须区分三个主要层次：遗传多样性、物种多样性和生态系统（栖息地）多样性。每个层次为衡量和解读生命丰富度提供了不同视角，也需要不同的保护策略。

2. Genetic Diversity | 遗传多样性

Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species. It arises from variation in the DNA sequences — including alleles, genes, and chromosomes — within and among populations of a species. It is the raw material for natural selection and adaptive evolution.

遗传多样性是指一个物种遗传组成中遗传特征的总和。它源于物种种群内部及种群之间 DNA 序列的变异，包括等位基因、基因和染色体层面的差异。它是自然选择和适应性进化的原材料。

High genetic diversity allows populations to adapt to changing environments, resist diseases, and survive demographic fluctuations. Low genetic diversity, by contrast, increases the risk of inbreeding depression and extinction, as famously observed in cheetahs and the Mauritius kestrel.

高遗传多样性使种群能够适应环境变化、抵抗疾病并在种群数量波动中存活。相比之下，低遗传多样性会增加近交衰退和灭绝的风险，正如在猎豹和毛里求斯隼中著名的观察结果所示。

A key quantitative measure in CIE is the number of different alleles of a gene in a population. The allele frequency, conventionally denoted by p and q in Hardy-Weinberg equations, reflects genetic diversity. A higher number of alleles per locus indicates greater genetic diversity.

CIE 考纲中的一个关键定量指标是一个种群中某个基因的不同等位基因数目。通常用 Hardy-Weinberg 方程中的 p 和 q 表示等位基因频率，较高的每基因座等位基因数目意味着更大的遗传多样性。

Allele frequency = (number of copies of an allele) / (total number of alleles in the population)

等位基因频率 = （某等位基因拷贝数）/（种群中该基因位点的总等位基因数）

3. Sources of Genetic Variation | 遗传变异的来源

Genetic variation arises primarily from three mechanisms: mutation, meiosis (including crossing over and independent assortment), and random fertilisation. Mutations are the ultimate source of new alleles; without them, evolution cannot proceed.

遗传变异主要来源于三种机制：突变、减数分裂（包括交叉互换和自由组合）以及随机受精。突变是新等位基因的最终来源；没有突变，进化便无法进行。

Mutation: changes in DNA base sequences, e.g. substitution, insertion, deletion. These create new alleles.
突变：DNA 碱基序列的变化，如替换、插入、缺失，从而产生新等位基因。
Crossing over: exchange of genetic material between non-sister chromatids during prophase I, producing recombinant chromosomes.
交叉互换：在减数第一次分裂前期，非姐妹染色单体之间交换遗传物质，产生重组染色体。
Independent assortment: random alignment of homologous chromosomes at the metaphase plate, generating new combinations of maternal and paternal chromosomes.
自由组合：同源染色体在赤道板上的随机排列，产生母源和父源染色体的新组合。
Random fertilisation: any sperm can fuse with any egg, greatly increasing genotypic variation.
随机受精：任意精子可与任意卵子融合，极大地增加了基因型变异。

For example, in humans, independent assortment alone can produce 2²³ possible gamete combinations, and fertilisation multiplies this to over 64 trillion possible zygotic genotypes — ignoring crossing over. This staggering number illustrates the enormous genetic diversity that is possible within a single species.

以人类为例，仅自由组合一项就能产生 2²³ 种可能的配子组合，而受精将这一数字放大至超过 64 万亿种可能的合子基因型——这还未考虑交叉互换。这一惊人的数字说明单一物种内部可能存在多么巨大的遗传多样性。

4. Species Diversity | 物种多样性

Species diversity refers to the variety of species within a particular habitat or ecosystem. It has two components: species richness (the number of different species) and species evenness (the relative abundance of each species). Both components are essential for a complete understanding of an ecosystem’s biodiversity.

物种多样性是指特定栖息地或生态系统中物种的多样性。它包含两个组成部分：物种丰富度（不同物种的数量）和物种均匀度（各物种的相对丰度）。这两个组成部分对于全面理解生态系统的生物多样性都是必不可少的。

Consider two forests: Forest A has 10 species, each with 100 individuals. Forest B has 10 species, but one species has 901 individuals while the other nine have only 11 each. Both have the same species richness (10), but Forest A has much higher evenness and therefore, by most indices, greater species diversity.

考虑两片森林：森林 A 有 10 个物种，每个物种有 100 个个体。森林 B 也有 10 个物种，但其中一个物种有 901 个个体，而其余九个物种各只有 11 个个体。两者的物种丰富度相同（均为10），但森林 A 的均匀度要高得多，因此根据大多数指数，其物种多样性也更高。

Species diversity can be measured using indices such as Simpson’s Diversity Index and the Shannon-Wiener Index. Simpson’s Index, given below, is particularly favoured in CIE past papers because it accounts for both richness and evenness.

物种多样性可以用辛普森多样性指数和香农-维纳指数等指数来衡量。辛普森指数（如下所示）在 CIE 历年真题中特别受青睐，因为它同时考虑了丰富度和均匀度。

D = 1 − Σ (nᵢ/N)²

where nᵢ is the number of individuals of species i and N is the total number of individuals of all species. D ranges from 0 (no diversity) to 1 (infinite diversity). A higher D value indicates greater species diversity.

其中 nᵢ 是物种 i 的个体数，N 是所有物种的总个体数。D 的取值范围从 0（无多样性）到 1（无限多样性）。D 值越高表明物种多样性越大。

5. Ecosystem Diversity | 生态系统多样性

Ecosystem (or habitat) diversity refers to the variety of habitats, communities, and ecological processes in the biosphere. It encompasses the range of different ecosystems — tropical rainforests, coral reefs, grasslands, tundra, mangroves, and so forth — each with its own characteristic species assemblage and physical environment.

生态系统（或栖息地）多样性是指生物圈中栖息地、群落和生态过程的多样性。它涵盖不同生态系统的范围——热带雨林、珊瑚礁、草原、苔原、红树林等等——每个生态系统都有其特有的物种组合和物理环境。

Ecosystem diversity is the broadest level of biodiversity. It focuses not just on the number of species but on the variety of niches, trophic levels, energy flows, and nutrient cycling patterns. A landscape with many different ecosystem types generally supports higher overall biodiversity.

生态系统多样性是生物多样性最宽泛的层次。它不仅关注物种数量，还关注生态位、营养级、能量流动和养分循环模式的多样性。拥有多种不同类型生态系统的景观通常能支持更高的总体生物多样性。

For instance, an area containing a river, a forest, and a meadow supports more species overall than an area equal in size covered entirely by uniform grassland. The river provides aquatic niches, the forest provides vertical strata for arboreal species, and the meadow supports open-country specialists.

例如，一个包含河流、森林和草甸的区域，其总体支持的物种数量要多于同等面积完全被单一草地覆盖的区域。河流提供水生生态位，森林为树栖物种提供垂直层次，草甸则支持开阔地带的特化物种。

6. Comparing the Three Levels | 三个层次的比较

Level	Scale	Key Measure	Example
Genetic	Within a species	Number of alleles per locus	Wheat cultivars with different disease-resistance alleles
Species	Within a community	Species richness and evenness	A coral reef with 300 fish species
Ecosystem	Across a landscape	Number and extent of habitats	A national park containing forest, wetland, and savanna
层次	尺度	主要度量指标	实例
遗传	物种内部	每个基因座的等位基因数目	具有不同抗病等位基因的小麦品种
物种	群落内部	物种丰富度和均匀度	拥有300种鱼类的珊瑚礁
生态系统	景观尺度	栖息地的数量和范围	包含森林、湿地和热带草原的国家公园

It is essential to recognise that these levels are interdependent. Loss of ecosystem diversity often reduces species diversity, which in turn shrinks the genetic pool available for adaptation. Conversely, conserving genetic diversity within a species supports the persistence of that species within its ecosystem.

必须认识到这些层次是相互依存的。生态系统多样性的丧失往往会减少物种多样性，进而缩小可用于适应的基因库。反之，保护物种内部的遗传多样性有助于该物种在其生态系统中的持续存在。

7. Biodiversity and Evolution | 生物多样性与进化

Biodiversity is both a product and a driver of evolution. Over geological time, speciation generates new species, increasing species diversity, while extinction removes species, decreasing it. The balance between these rates determines present-day biodiversity patterns.

生物多样性既是进化的产物，也是进化的驱动力。在地质时间尺度上，物种形成产生新物种，增加物种多样性；而灭绝则移除物种，减少物种多样性。这两者之间的平衡决定了当今的生物多样性格局。

The process of natural selection acts on genetic diversity: individuals with advantageous alleles are more likely to survive and reproduce, thereby increasing the frequency of those alleles in the next generation. This adaptive evolution is only possible because genetic diversity provides the raw material.

自然选择作用于遗传多样性：具有有利等位基因的个体更有可能存活和繁殖，从而增加这些等位基因在后代中的频率。这种适应性进化只有在遗传多样性提供原材料的情况下才可能发生。

Island biogeography provides a classic illustration. Islands typically have lower species diversity than equivalent mainland areas due to isolation and limited area. However, islands often exhibit high endemism — species found nowhere else — because isolated populations evolve independently, as seen in Darwin’s finches of the Galápagos.

岛屿生物地理学提供了一个经典例证。由于隔离和面积有限，岛屿的物种多样性通常低于同等面积的大陆地区。然而，岛屿常常表现出高度的特有性——即其他地方找不到的物种——因为隔离的种群独立进化，正如加拉帕戈斯群岛的达尔文雀。

8. Measuring Species Diversity: Simpson’s Index Worked Example | 物种多样性的测量：辛普森指数计算示例

Let us work through a CIE-style calculation. Suppose a student samples a grassland and records the following counts: daisy (40), clover (30), buttercup (20), grass (10). Total N = 100.

让我们完成一道 CIE 风格的计算。假设一名学生取样一片草地并记录如下数量：雏菊 40，三叶草 30，毛茛 20，禾草 10。总数 N = 100。

Calculate Σ(nᵢ/N)² = (40/100)² + (30/100)² + (20/100)² + (10/100)² = 0.16 + 0.09 + 0.04 + 0.01 = 0.30.

计算 Σ(nᵢ/N)² = (40/100)² + (30/100)² + (20/100)² + (10/100)² = 0.16 + 0.09 + 0.04 + 0.01 = 0.30。

D = 1 − 0.30 = 0.70

If all four species were equally abundant (25 each), then Σ(nᵢ/N)² = 4 × (0.25)² = 0.25, and D = 0.75. The even community has a higher diversity index, demonstrating why evenness matters. In the exam, always show your substitution step and round your final answer appropriately.

如果四个物种都等丰度（各25），则 Σ(nᵢ/N)² = 4 × (0.25)² = 0.25，D = 0.75。均匀的群落具有更高的多样性指数，说明均匀度为何重要。在考试中，务必写出代入步骤并适当四舍五入最终答案。

9. Human Impact on Biodiversity | 人类活动对生物多样性的影响

Anthropogenic activities are currently reducing biodiversity at all three levels at an unprecedented rate. The major threats include habitat destruction, overexploitation, pollution, invasive species, and climate change — often remembered by the mnemonic HIPPO.

人类活动正以前所未有的速度在这三个层次上降低生物多样性。主要威胁包括栖息地破坏、过度开发、污染、入侵物种和气候变化——通常用助记符 HIPPO 来记忆。

Habitat loss: deforestation, drainage of wetlands, and urbanisation fragment and eliminate habitats, reducing ecosystem diversity.
栖息地丧失：森林砍伐、湿地排水和城市化使栖息地破碎化甚至消失，从而降低生态系统多样性。
Overexploitation: overfishing, hunting, and illegal wildlife trade reduce species populations and even drive species extinct.
过度开发：过度捕捞、狩猎和非法野生动物贸易减少物种种群，甚至导致物种灭绝。
Pollution: eutrophication from fertiliser runoff, oil spills, and plastic waste poison organisms and disrupt food webs.
污染：化肥径流导致的富营养化、石油泄漏和塑料废物毒害生物并干扰食物网。
Invasive species: non-native species outcompete, prey on, or hybridise with native species, eroding species and genetic diversity.
入侵物种：外来物种与本地物种竞争、捕食或杂交，侵蚀物种和遗传多样性。
Climate change: shifting temperature and precipitation patterns alter habitats faster than species can adapt or disperse.
气候变化：温度和降水格局的变化使栖息地改变的速度超过物种适应或迁移的速度。

Genetic diversity is also eroded when populations become small and isolated. Genetic drift, inbreeding, and the founder effect reduce allelic diversity, compromising the long-term evolutionary potential of species.

当种群变得小而孤立时，遗传多样性也会被侵蚀。遗传漂变、近交和奠基者效应会减少等位基因多样性，损害物种长期进化的潜力。

10. Conservation Strategies | 保护策略

Conservation biology aims to preserve biodiversity at all levels. In situ conservation protects species and habitats in their natural environment, whereas ex situ conservation removes species from their natural habitats for managed breeding or storage.

保护生物学的目标是在所有层次上保存生物多样性。就地保护是在自然环境中保护物种和栖息地，而异地保护则是将物种从其自然栖息地移出进行人工繁殖或保存。

In Situ \| 就地保护	Ex Situ \| 异地保护
National parks and nature reserves	Zoos and botanic gardens
国家公园和自然保护区	动物园和植物园
Marine protected areas	Seed banks and gene banks
海洋保护区	种子库和基因库
Wildlife corridors linking fragmented habitats	Captive breeding and reintroduction programmes
连接破碎化栖息地的野生动物廊道	人工繁殖和再引入计划

In situ conservation is generally preferred because it maintains evolutionary processes and ecological interactions. However, ex situ measures are vital for critically endangered species that cannot survive in the wild due to threats such as disease or poaching.

就地保护通常更受青睐，因为它维持了进化过程和生态相互作用。然而，对于因疾病或盗猎等威胁而无法在野外存活的极度濒危物种，异地保护措施至关重要。

Genetic diversity preservation often relies on gene banks. For crops, seed banks store dormant seeds under controlled conditions; for animals, sperm, eggs, and embryos may be cryopreserved. The Svalbard Global Seed Vault in Norway is a famous example, holding over one million seed samples.

遗传多样性的保存通常依赖基因库。对于农作物，种子库在受控条件下储存休眠种子；对于动物，精液、卵子和胚胎可被冷冻保存。挪威的斯瓦尔巴全球种子库便是一个著名例子，保存着超过一百万份种子样本。

11. Biodiversity in the CIE Examination | CIE 考试中的生物多样性考点

Past papers reveal that CIE commonly tests biodiversity in three ways: (1) defining the three levels and giving examples; (2) calculating Simpson’s Index from data provided; and (3) evaluating conservation strategies with reference to biodiversity levels. You should be able to answer all three with confidence.

历年真题显示，CIE 通常从三个方面考查生物多样性：（1）定义三个层次并举例；（2）根据提供的数据计算辛普森指数；（3）联系生物多样性层次评价保护策略。你应当能够自信地回答这三类问题。

For definition questions, never confuse species richness with species diversity. Species richness is a simple count of species, whereas species diversity incorporates both richness and evenness. This distinction frequently appears in multiple-choice questions.

对于定义题，切勿混淆物种丰富度与物种多样性。物种丰富度只是物种数量的简单计数，而物种多样性综合了丰富度和均匀度。这一区分经常出现在选择题中。

For data-response questions, show all working. The examiner awards method marks even if your final calculation is slightly off. For essay questions, always frame your answer around all three levels of biodiversity — genetic, species, and ecosystem — to demonstrate syllabus coverage.

对于数据回应题，务必展示全部计算过程。即使最终计算略有偏差，考官也会给予方法分。对于论述题，始终围绕生物多样性的三个层次——遗传、物种和生态系统——组织答案，以显示对考纲的全面覆盖。

12. Conclusion | 结语

Biodiversity operates at three interconnected levels: genetic, species, and ecosystem. Each level contributes uniquely to the resilience and functioning of life on Earth. Genetic diversity fuels adaptation; species diversity stabilises communities; ecosystem diversity sustains the biosphere’s life-support systems.

生物多样性在三个相互关联的层次上运作：遗传、物种和生态系统。每个层次都独特地贡献于地球生命的韧性和功能。遗传多样性驱动适应；物种多样性稳定群落；生态系统多样性维持生物圈的生命支持系统。

As the CIE syllabus emphasises, a thorough grasp of these levels — their definitions, measurement, interdependence, threats, and conservation — is essential not only for examination success but also for informed global citizenship in an era of unprecedented biodiversity loss.

正如 CIE 考纲所强调的，深入掌握这些层次的定义、测量、相互依存、威胁和保护，不仅对考试成功至关重要，也是在这个生物多样性空前丧失的时代做一个有知识的全球公民所必需的。

We hope this structured guide strengthens your revision. Remember to practise past-paper questions on Simpson’s Index and conservation strategies to consolidate your understanding.

我们希望这篇结构化指南能强化你的复习。记得练习关于辛普森指数和保护策略的真题，以巩固你的理解。

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CIE A-Level Biology: Levels of Biodiversity | CIE A-Level 生物：生物多样性的层次