📚 Biodiversity, Classification and Conservation | 生物多样性、分类与保护
Biodiversity, classification and conservation form a core topic in Cambridge A-Level Biology. This unit links field ecology, molecular biology and global policy, requiring you to understand both conceptual definitions and practical methods for measuring and protecting biodiversity.
生物多样性、分类与保护是剑桥 A-Level 生物的核心主题。本单元将野外生态学、分子生物学和全球政策联系起来，要求你既理解概念定义，也掌握测量和保护生物多样性的实用方法。
1. Defining Biodiversity: Species, Genetic and Ecosystem Diversity | 生物多样性的定义：物种、遗传与生态系统多样性
Biodiversity is the variety of living organisms on Earth, including the variation within species, between species and between ecosystems. It is usually divided into three levels: species diversity, genetic diversity and ecosystem diversity.
生物多样性是指地球上生物体的多样性，包括物种内、物种间以及生态系统间的变异。它通常分为三个层次：物种多样性、遗传多样性和生态系统多样性。
Species diversity is the number of different species in a community and how evenly individuals are distributed among those species. A community dominated by one or two species has lower species diversity than one with many equally abundant species.
物种多样性指群落中不同物种的数量以及个体在这些物种间的分布均匀程度。由一两个物种主导的群落，其物种多样性低于拥有许多数量相近物种的群落。
Genetic diversity is the range of alleles present in a species or population. It determines the ability of a population to adapt to environmental change, resist disease and survive long-term, so small isolated populations with low genetic diversity are particularly vulnerable.
遗传多样性指一个物种或种群中等位基因的范围。它决定种群适应环境变化、抵抗疾病和长期存活的能力，因此遗传多样性低的小型隔离种群尤其脆弱。
Ecosystem diversity refers to the variety of habitats, biotic communities and ecological processes in the biosphere. Different ecosystems such as rainforests, coral reefs and peat bogs each provide distinct niches and services.
生态系统多样性指生物圈中栖息地、生物群落和生态过程的多样性。雨林、珊瑚礁和泥炭沼泽等不同生态系统各自提供独特的生态位和服务。
2. Measuring Species Diversity: Richness, Evenness and Simpson’s Index | 物种多样性的测量：丰富度、均匀度与辛普森指数
Species richness is simply the total number of different species recorded in a given sample or habitat. Although easy to obtain, richness ignores how many individuals belong to each species.
物种丰富度只是在一个给定样本或栖息地中记录到的不同物种的总数。虽然容易获得，但丰富度忽略了每个物种有多少个体。
Species evenness describes the relative abundance of species. If one species has 95 individuals and four others have only one each, richness is 5 but evenness is very low, so the community is not considered diverse.
物种均匀度描述各物种的相对丰度。如果一个物种有95个个体，而另外四个物种各只有1个个体，丰富度为5，但均匀度很低，因此该群落不被认为是多样的。
Simpson’s index of diversity combines richness and evenness into one value between 0 and 1. The formula is:
辛普森多样性指数将丰富度和均匀度合并为一个0到1之间的数值。公式为：
D = 1 − Σ(n ÷ N)²
Here n is the total number of individuals of a particular species, N is the total number of individuals of all species, and Σ means ‘sum of’. A higher D value indicates greater biodiversity because no single species dominates the sample.
其中 n 是某一特定物种的个体总数，N 是所有物种的个体总数，Σ 表示“求和”。D 值越高表示生物多样性越大，因为没有单一物种主导样本。
For example, a pond sample contains 20 frogs, 30 newts and 50 fish, so N = 100. The calculation is D = 1 − [(20/100)² + (30/100)² + (50/100)²] = 1 − (0.04 + 0.09 + 0.25) = 0.62.
例如，一个池塘样本含有20只蛙、30只蝾螈和50条鱼，因此 N = 100。计算为 D = 1 − [(20/100)² + (30/100)² + (50/100)²] = 1 − (0.04 + 0.09 + 0.25) = 0.62。
In exam questions, you may be given species abundance data and asked to calculate D. Always show each fraction, square it, sum all squares, and then subtract from 1 to gain full method marks.
在考试题中，可能会给出物种丰度数据并要求计算 D。务必展示每个分数、将其平方、将所有平方相加，然后用 1 减去，以获得完整的方法分。
3. Sampling Biodiversity: Random and Systematic Techniques | 生物多样性取样：随机与系统方法
Because it is usually impossible to count every individual in a habitat, ecologists estimate biodiversity using sampling techniques. The method must be repeatable and minimise bias to give valid results.
由于通常不可能计数栖息地中的每个个体，生态学家使用取样技术来估算生物多样性。方法必须可重复并尽量减少偏差，才能给出有效结果。
Random sampling uses randomly placed quadrats to avoid sampling bias. A larger number of samples gives a more reliable estimate, but the time and effort required must be balanced against accuracy.
随机取样使用随机放置的样方来避免取样偏差。样本数量越多，估算越可靠，但必须在准确性与所需时间和精力之间取得平衡。
Systematic sampling, such as a belt transect or line transect, places quadrats at regular intervals along a line. This is useful when investigating changes in species distribution along an environmental gradient, such as from a seashore to sand dunes.
系统取样（如样带取样）沿一条线以固定间隔放置样方。这在研究物种分布沿环境梯度变化时很有用，例如从海岸到沙丘的变化。
When sampling, it is important to record the same variables each time: species present, number of individuals, percentage cover, and abiotic factors such as light intensity, soil pH or water content. Repeating samples helps identify anomalies and calculate mean values.
取样时，每次记录相同的变量很重要：存在的物种、个体数量、覆盖百分比，以及光照强度、土壤 pH 或含水量等非生物因素。重复取样有助于识别异常值并计算平均值。
4. The Five Kingdoms and Three Domains | 五界系统与三域系统
Historically, organisms were classified into five kingdoms: Prokaryotae, Protoctista, Fungi, Plantae and Animalia. This system is based mainly on cell structure, body organisation and mode of nutrition.
传统上，生物被分为五界：原核生物界、原生生物界、真菌界、植物界和动物界。该系统主要基于细胞结构、身体组织和营养方式。
Molecular biology and genetic analysis led to the three-domain system proposed by Carl Woese: Bacteria, Archaea and Eukarya. This system reflects fundamental differences in ribosomal RNA sequences and cell biochemistry.
分子生物学和遗传分析促使 Carl Woese 提出了三域系统：细菌域、古菌域和真核生物域。该系统反映了核糖体 RNA 序列和细胞生化方面的根本差异。
Bacteria and Archaea are both prokaryotic, meaning they lack a membrane-bound nucleus and membrane-bound organelles. However, Archaea have distinct membrane lipids, RNA polymerase, and cell wall composition; many archaea are extremophiles living in hot springs, salt lakes or anaerobic environments.
细菌和古菌都是原核生物，意味着它们缺乏膜包被的细胞核和膜包被的细胞器。然而，古菌具有独特的膜脂、RNA 聚合酶和细胞壁组成；许多古菌是生活在温泉、盐湖或厌氧环境中的嗜极生物。
The domain Eukarya includes all organisms whose cells contain a true nucleus and membrane-bound organelles. It contains the kingdoms Protoctista, Fungi, Plantae and Animalia. Viruses are not classified in any domain because they are not cellular organisms.
真核生物域包括所有细胞含有真正细胞核和膜包被细胞器的生物。它包含原生生物界、真菌界、植物界和动物界。病毒不属于任何域，因为它们不是细胞生物。
5. Binomial Nomenclature and Taxonomic Hierarchy | 双名法与分类等级
Binomial nomenclature is the formal system of naming species using two Latin words: the genus name followed by the species epithet. For example, humans are Homo sapiens and the domestic dog is Canis familiaris.
双名法是用两个拉丁词正式命名物种的系统：属名后接种加词。例如，人类是 Homo sapiens，家犬是 Canis familiaris。
The scientific name is written in italics when typed or underlined when handwritten. The genus always starts with a capital letter, while the species epithet starts with a lower-case letter, even if it is derived from a person’s name.
学名在打印时用斜体，手写时用下划线。属名首字母始终大写，而种加词首字母小写，即使它来自人名也不例外。
The taxonomic hierarchy is a series of increasingly inclusive groups used to classify organisms. From broadest to most specific, the levels are: domain, kingdom, phylum, class, order, family, genus, species.
分类等级是一系列包含范围逐渐缩小的类群，用于对生物进行分类。从最广泛到最具体，层级为：域、界、门、纲、目、科、属、种。
A common mnemonic to remember the order is ‘Dear King Phillip Came Over For Good Soup’. In a classification question, always move from the broadest category to the most specific and use correct scientific formatting.
记住顺序的常用助记口诀是 ‘Dear King Phillip Came Over For Good Soup’。在分类题中，始终从最广泛的类别到最具体的类别，并使用正确的科学格式。
6. Phylogeny and Molecular Classification | 系统发育与分子分类
Phylogeny is the evolutionary history and relationships among species or groups. It is often represented as a branching diagram called a phylogenetic tree, where branch points indicate common ancestors.
系统发育是指物种或类群之间的进化历史和关系。它通常用称为系统发育树的分支图表示，分支点表示共同祖先。
Traditionally, classification relied on observable morphology and anatomy, but analogous structures can be misleading because they arise from convergent evolution rather than shared ancestry.
传统分类依赖可观察的形态和解剖特征，但同功结构可能产生误导，因为它们来自趋同进化而非共同祖先。
Molecular classification compares biological molecules such as DNA, RNA and proteins. The more similar the sequences between two species, the more recently they shared a common ancestor. This provides objective evidence for evolutionary relationships.
分子分类比较 DNA、RNA 和蛋白质等生物分子。两个物种之间的序列越相似，它们拥有共同祖先的时间越近。这为进化关系提供了客观证据。
Conserved sequences, such as ribosomal RNA genes, are particularly useful because they change very slowly and can be compared across distantly related organisms. Molecular data have revealed, for example, that fungi are more closely related to animals than to plants.
核糖体 RNA 基因等保守序列特别有用，因为它们变化非常缓慢，可以用于远缘生物之间的比较。例如，分子数据揭示真菌与动物的亲缘关系比与植物更近。
7. Conservation: Why Biodiversity Matters | 保护：生物多样性为何重要
Conservation is the protection, management and restoration of biodiversity to ensure its sustainable use for present and future generations. It includes in situ conservation in natural habitats and ex situ conservation outside natural habitats.
保护是对生物多样性的保护、管理和恢复，以确保其为当代和后代可持续利用。它包括在自然栖息地进行的就地保护，以及在自然栖息地之外进行的迁地保护。
Biodiversity provides essential ecosystem services: pollination of crops, nutrient cycling, climate regulation, water purification, soil formation and flood control. Without these services, food production and human health would collapse.
生物多样性提供基本的生态系统服务：作物授粉、养分循环、气候调节、水体净化、土壤形成和防洪。如果没有这些服务，粮食生产和人类健康将会崩溃。
Biodiversity also has direct economic value through agriculture, fisheries, timber, medicine and tourism. Many pharmaceuticals are derived from plant or microbial compounds, so losing species may mean losing potential treatments.
生物多样性还通过农业、渔业、木材、医药和旅游具有直接经济价值。许多药物来自植物或微生物化合物，因此物种丧失可能意味着失去潜在的治疗方法。
In addition, biodiversity has aesthetic, cultural, recreational and ethical value. Many people believe species have a right to exist independent of their usefulness to humans, and indigenous cultures depend on local biodiversity for identity and tradition.
此外，生物多样性具有美学、文化、娱乐和伦理价值。许多人认为物种有权独立于其对人类的有用性而存在，而土著文化依赖当地生物多样性来维持身份和传统。
8. Threats to Biodiversity: Habitat Loss, Invasive Species and Overexploitation | 生物多样性面临的威胁：栖息地丧失、入侵物种与过度开发
The major threats to biodiversity are habitat destruction, overexploitation, pollution, invasive species and climate change. These pressures often interact, causing rapid declines in populations and species extinctions.
生物多样性面临的主要威胁是栖息地破坏、过度开发、污染、入侵物种和气候变化。这些压力常常相互作用，导致种群迅速下降和物种灭绝。
Habitat loss is the biggest threat globally. Deforestation for timber and agriculture, wetland drainage, urban expansion and mining fragment or destroy the places species need to feed, breed and shelter.
栖息地丧失是全球最大的威胁。为获取木材和农业用地而砍伐森林、排干湿地、城市扩张和采矿，使物种觅食、繁殖和栖息的场所被碎片化或破坏。
Overexploitation occurs when organisms are removed from the wild at a faster rate than they can reproduce. Examples include overfishing, illegal poaching of elephants for ivory and tigers for body parts, and unsustainable logging of tropical hardwoods.
过度开发是指生物从野外被移除的速度超过其繁殖速度。例子包括过度捕捞、为获取象牙而非法偷猎大象、为获取身体部位而偷猎老虎，以及不可持续地采伐热带硬木。
Invasive alien species are introduced, often by human activity, into ecosystems where they have no natural predators. They compete with native species for resources,
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