📚 Biodiversity | 生物多样性
Biodiversity, or biological diversity, describes the variety of life on Earth at all levels, from genes to ecosystems. It is fundamental to the resilience of life-support systems, providing essential services such as clean air, water, pollination and climate regulation. In A-Level Biology, understanding biodiversity involves not only recognising the richness of species but also quantifying it, analysing threats and evaluating conservation strategies.
生物多样性指地球上从基因到生态系统等各个层次的生命多样性。它对生命支持系统的恢复力至关重要，提供着清洁空气、水、授粉和气候调节等基础服务。在 A-Level 生物学中，理解生物多样性不仅要认识物种的丰富程度，还要加以量化、分析威胁因素并评估保护策略。
1. What is Biodiversity? | 什么是生物多样性？
Biodiversity is usually considered at three interconnected levels: ecosystem diversity, species diversity and genetic diversity.
生物多样性通常从三个相互关联的层次加以考量：生态系统多样性、物种多样性和遗传多样性。
Ecosystem diversity refers to the variety of habitats, biological communities and ecological processes in the living world. A landscape containing woodlands, wetlands, grasslands and rivers has high ecosystem diversity.
生态系统多样性指生物世界中栖息地、生物群落和生态过程的多样性。同时包含林地、湿地、草原与河流的景观便具有很高的生态系统多样性。
Species diversity combines species richness — the number of different species present — and species evenness, which is the relative abundance of each species. A community with many species all in similar numbers is more diverse than one dominated by a single species.
物种多样性结合了物种丰富度（即存在的不同物种数量）与物种均匀度（各物种的相对丰度）。一个拥有许多物种且数量相近的群落，远比单一物种占优势的群落更具多样性。
Genetic diversity is the total number of different alleles in a gene pool. Populations with higher genetic diversity have a wider range of phenotypes, increasing the chance that some individuals will survive environmental changes.
遗传多样性指基因库中所有不同等位基因的总和。遗传多样性越高的种群拥有越广的表型范围，从而增大某些个体在环境变化中存活下来的机会。
2. Species Concepts and Classification | 物种概念与分类
The biological species concept defines a species as a group of organisms that can interbreed to produce fertile offspring. This definition has limitations, particularly for asexual organisms and ring species, so morphological and phylogenetic species concepts are also used.
生物种概念将一个物种定义为能够相互交配并产生可育后代的一群生物。这一定义对无性繁殖生物及环种存在局限性，因此也会使用形态学种概念和系统发生种概念。
Classification organises biodiversity into a hierarchical system. The three-domain system proposed by Carl Woese divides life into Bacteria, Archaea and Eukarya based on differences in ribosomal RNA sequences. Within Eukarya, organisms are further grouped into kingdoms: Animalia, Plantae, Fungi and Protoctista.
分类将生物多样性纳入等级体系中。卡尔·乌斯提出的三域系统依据核糖体 RNA 序列的差异，将生物分为细菌域、古菌域和真核域。在真核域内，生物又进一步划分到动物界、植物界、真菌界和原生生物界等。
Each species is given a unique binomial name consisting of its genus and species, such as Homo sapiens. This standardised naming allows scientists worldwide to communicate unambiguously about biodiversity.
每个物种拥有一个由属名和种加词组成的独特双名，如 Homo sapiens。这一标准化命名使全球科学家能够清晰地交流生物多样性信息。
3. Species Richness and Evenness | 物种丰富度与均匀度
Species richness (S) is simply a count of the number of different species in a habitat. A coral reef has far greater richness than a polar ice sheet. However, richness alone does not reflect the full picture of diversity because it ignores how individuals are distributed among species.
物种丰富度 (S) 仅仅是栖息地中不同物种的数量统计。珊瑚礁的丰富度远高于极地冰盖。然而，丰富度本身不能反映多样性的全貌，因为它忽略了各物种间的个体分布状况。
Species evenness describes the balance of relative abundances. Two communities may have the same richness, but the one in which individuals are spread more evenly across species is considered more diverse. Low evenness often indicates that one or a few species dominate, perhaps due to disturbance or invasive species.
物种均匀度描述相对丰度的均衡程度。两个群落的丰富度可能相同，但个体在各物种间分布更均匀的那个被视为更多样。低均匀度往往表明一个或少数物种占主导地位，这可能是干扰或入侵物种所致。
Conservation ecologists use both richness and evenness to monitor ecosystem health. A sudden decline in evenness can serve as an early warning of environmental stress, even before species are lost.
保护生态学家利用丰富度和均匀度来监测生态系统健康。均匀度的突然下降可作为环境压力的早期预警，甚至出现在物种消失之前。
4. Simpson's Index of Diversity | 辛普森多样性指数
Simpson's Index of Diversity (D) is a quantitative measure that considers both species richness and evenness. The formula produces a value between 0 and 1, where values closer to 1 indicate higher diversity.
辛普森多样性指数 (D) 是一种综合了物种丰富度与均匀度的量化指标。该公式得出 0 到 1 之间的数值，越接近 1 表示多样性越高。
D = 1 – [ Σ n(n–1) ] / [ N(N–1) ]
er of individuals of a particular species, N = total number of individuals of all species.
式中 n 为特定物种的个体数，N 为所有物种的个体总数。
For example, consider two small woodland plots. Plot A contains three species with individual counts 5, 5, 5. Plot B also contains three species but with counts 13, 1, 1.
例如，考虑两块小林地。样地 A 包含三个物种，个体数分别为 5, 5, 5。样地 B 同样包含三个物种，但个体数为 13, 1, 1。
| Plot A | Species: n=5,5,5; N=15; Σ n(n–1) = 5×4 + 5×4 + 5×4 = 60; D = 1 – 60/(15×14) = 1 – 60/210 ≈ 0.714 |
| Plot B | Species: n=13,1,1; N=15; Σ n(n–1) = 13×12 + 1×0 + 1×0 = 156; D = 1 – 156/(15×14) = 1 – 156/210 ≈ 0.257 |
The much lower D in Plot B reflects that one species dominates, reducing overall diversity despite equal richness.
样地 B 的 D 值低得多，反映出一个物种占优势，尽管物种丰富度相同，整体多样性却被拉低。
5. Sampling Biodiversity | 生物多样性取样
Assessing biodiversity in the field requires reliable sampling techniques. For stationary organisms such as plants, quadrats — square frames placed randomly or along a transect — are used to estimate species frequency, density and percentage cover. Transect lines help reveal zonation patterns across environmental gradients, like changes in vegetation from a shoreline inland.
野外评估生物多样性需要可靠的取样技术。对于植物等固着生物，可使用样方（方形框架）随机或沿样线放置，来估算物种频度、密度和覆盖度百分比。样线有助于揭示沿环境梯度的带状分布格局，如从湖岸向内陆的植被变化。
For mobile animals, the mark-release-recapture method estimates population size using the Lincoln index:
对于活动动物，标记-释放-重捕法利用林肯指数估算种群大小：
N = (M × C) / R
individuals recaptured in the second sample. The method assumes marks are not lost, marked individuals mix evenly with the population, and the population is closed between samples.
其中 M 为第一次捕获、标记并释放的个体数，C 为第二次捕获的总数，R 为第二次捕获中已标记个体的数量。该方法假设标记不丢失、标记个体与种群均匀混合，且取样期间种群封闭。
All sampling methods rely on randomness to avoid bias, and repeated samples increase the reliability of diversity estimates.
所有取样方法都依赖随机性以避免偏差，且重复取样能提高多样性估算的可靠性。
6. Genetic Diversity within Species | 物种内的遗传多样性
Genetic diversity within a species can be measured by the proportion of heterozygous loci or the number of alleles per locus in a population. It forms the raw material for natural selection and adaptation. Low genetic diversity, often caused by small population size, bottlenecks or inbreeding, reduces a population's ability to survive disease outbreaks or climate shifts.
物种内的遗传多样性可通过杂合位点比例或每个位点的等位基因数量来衡量。它为自然选择和适应提供了原始材料。低遗传多样性通常由小种群规模、瓶颈效应或近交造成，削弱了种群抵御疾病暴发或气候变化的能力。
For example, the cheetah (Acinonyx jubatus) underwent a severe genetic bottleneck around 10,000 years ago, resulting in extremely limited allelic diversity. This makes contemporary cheetahs highly susceptible to infectious diseases and reproductive problems.
例如，猎豹在大约 10,000 年前经历了严重的遗传瓶颈，导致等位基因多样性极低。这使得当代猎豹极易受传染病和繁殖问题的困扰。
Maintaining genetic diversity is a key goal of conservation biology, achieved by protecting large, interconnected habitats that permit gene flow between populations.
维持遗传多样性是保护生物学的核心目标，通过保护大型且相互连通的栖息地来实现种群间的基因流动。
7. Ecosystem Biodiversity and Niches | 生态系统多样性与生态位
Ecosystem biodiversity refers to the range of different ecosystems within a region, including the physical conditions and the species that inhabit them. Greater habitat heterogeneity creates more ecological niches — the specific role of a species in its community — and thus supports higher biodiversity.
生态系统多样性指一个区域内不同生态系统的范围，包括物理条件与栖居其中的物种。较高的栖息地异质性创造出更多的生态位（物种在群落中的特定角色），从而支撑更高的生物多样性。
A species' fundamental niche is the full set of environmental conditions under which it can potentially survive, while its realised niche is the narrower set it actually occupies due to competition and other biotic interactions. The coexistence of many species in habitats such as tropical rainforests is partly explained by niche differentiation, which reduces direct competition.
一个物种的基础生态位是它理论上能生存的全部环境条件集合，而实际生态位则因竞争和其他生物互作而更窄。热带雨林等栖息地中众多物种的共存，部分可用减少直接竞争的生态位分化来解释。
Loss of ecosystem diversity, such as the draining of wetlands, not only reduces habitat area but also eliminates entire suites of niches, driving species extinction.
生态系统多样性的丧失，例如湿地排干，不仅缩小了栖息地面积，还消除了整套生态位，促使物种灭绝。
8. Threats to Biodiversity | 生物多样性面临的威胁
Habitat loss is the single greatest threat to biodiversity, driven by deforestation, agriculture, urbanisation and dam construction. Fragmentation reduces population sizes and disrupts migration routes, making species more vulnerable to extinction.
栖息地丧失是对生物多样性最大的单一威胁，毁林、农业扩张、城市化和水坝建设是其驱动因素。片段化导致种群规模缩小、迁徙路线中断，使物种更易灭绝。
Over-exploitation, such as overfishing and the illegal wildlife trade, removes individuals faster than populations can replenish. The collapse of the Newfoundland cod fishery illustrates the devastating impact of unsustainable harvest.
过度开发，如过度捕捞和非法野生动物贸易，以快于种群恢复的速度攫取个体。纽芬兰鳕鱼渔业的崩溃便是不持续捕猎灾难性后果的例证。
Invasive species outcompete native organisms, introduce diseases and alter habitats. The introduction of the brown tree snake to Guam led to the extinction of several endemic bird species.
入侵物种竞争排挤本土生物、传播疾病并改变栖息地。褐树蛇被引入关岛后，已导致数种特有鸟类的灭绝。
Pollution — including eutrophication caused by agricultural run-off, plastic debris and chemical contaminants — degrades habitats and poisons food webs. Climate change compounds all these threats by altering temperature and precipitation patterns, forcing species to shift ranges or face extinction.
污染——包括农业径流引起的富营养化、塑料碎片和化学污染物——使栖息地退化并毒害食物网。气候变化通过改变气温与降水格局，加剧了所有这些威胁，迫使物种转移分布区或面临灭绝。
9. Reasons for Conservation | 保护生物多样性的理由
Ethical reasons argue that species have an intrinsic right to exist, independent of their usefulness to humans. Many cultures and religions view humanity as stewards of nature.
伦理理由主张物种具有内禀的存在权利，不论其对人类是否有用。许多文化和宗教将人类视为自然的管理者。
Ecological reasons centre on ecosystem services: pollination of crops, purification of water, nutrient cycling, soil formation and climate regulation. The loss of a keystone species can disrupt these services and trigger cascading extinctions.
生态理由聚焦于生态系统服务：作物授粉、水体净化、养分循环、土壤形成与气候调节。关键种的消失会打乱这些服务，并引发级联灭绝。
Economic benefits include direct sources of food, fibres, medicines and ecotourism. Approximately 25% of modern medicines are derived from rainforest plants, yet only a small fraction of plant species have been screened for pharmaceutical potential. Conserving biodiversity preserves future options.
经济效益包括食物、纤维、医药和生态旅游的直接来源。现代药物中约有 25% 源自雨林植物，然而仅有极小部分植物物种被筛选过药物潜力。保护生物多样性就是保留未来的选择。
Aesthetic and cultural reasons recognise that natural landscapes and charismatic species inspire art, recreation and spiritual well-being. The loss of biodiversity impoverishes human experience.
美学与文化理由承认，自然景观与魅力物种能够启发艺术、休闲和精神福祉。生物多样性的丧失会使人类体验趋于贫瘠。
10. Conservation Methods: In Situ and Ex Situ | 保护方法：就地保护与迁地保护
In situ conservation protects species within their natural habitats. Establishing national parks, nature reserves and marine protected areas allows evolutionary processes to continue and preserves entire communities, not just target species. The Serengeti National Park in Tanzania protects vast savanna ecosystems and the annual wildebeest migration.
就地保护在物种自然栖息地内加以保护。建立国家公园、自然保护区和海洋保护区使得演化过程得以延续，并保护整个群落，而不仅仅是目标物种。坦桑尼亚的塞伦盖蒂国家公园就保护着广袤的稀树草原生态系统和年度角马迁徙。
However, in situ approaches can suffer from illegal poaching, encroachment and underfunding. Effective management requires community involvement and sustainable livelihoods for local people.
然而，就地保护可能遭遇偷猎、侵占和资金不足等困难。有效管理需要社区参与以及为当地居民提供可持续的生计。
Ex situ conservation involves protecting species outside their natural environment. Seed banks store seeds under cold, dry conditions to safeguard plant genetic resources; the Svalbard Global Seed Vault acts as a back-up for the world's crop diversity. Zoological gardens and aquariums maintain captive breeding programmes for endangered animals, with the long-term aim of reintroduction.
迁地保护涉及在自然生境之外保护物种。种子库在干冷条件下储存种子，以守卫植物遗传资源；斯瓦尔巴全球种子库为世界作物多样性提供备份。动物园和水族馆为濒危动物实施圈养繁殖计划，并以长期重引入为目标。
Ex situ methods provide an insurance against extinction but are costly and cannot replicate the full selective pressures of a natural environment. A combination of in situ and ex situ strategies is often the most robust conservation plan.
迁地方法为灭绝风险提供了一份保险，但成本高昂，且无法复制自然环境中的全部选择压力。就地与迁地策略相结合，往往是最为稳健的保护方案。
11. International Cooperation and Legislation | 国际合作与立法
The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) regulates cross-border trade in over 38,000 species through a system of permits. It aims to ensure that international trade does not threaten the survival of wild populations.
《濒危野生动植物种国际贸易公约》(CITES) 通过许可证制度管制着 38,000 多种物种的跨境贸易，旨在确保国际贸易不威胁野生种群的存续。
The Convention on Biological Diversity (CBD), signed at the 1992 Rio Earth Summit, commits signatory countries to conservation, sustainable use of biodiversity and fair sharing of benefits arising from genetic resources. The IUCN Red List of Threatened Species assesses the extinction risk of species and guides conservation prioritisation.
1992 年里约地球峰会签署的《生物多样性公约》(CBD) 要求缔约国致力于保护、可持续利用生物多样性，以及公平分享遗传资源产生的惠益。世界自然保护联盟 (IUCN) 濒危物种红色名录评估物种的灭绝风险，为确定保护优先顺序提供指导。
Despite these frameworks, enforcement remains challenging. Illegal wildlife trade and habitat destruction continue, underscoring the need for international collaboration, monitoring and public education.
尽管有这些框架，执法仍然充满挑战。非法野生动植物贸易和栖息地破坏依旧持续，这凸显了国际合作、监测与公众教育的必要性。
12. The Role of Biodiversity in Ecosystem Stability | 生物多样性在生态系统稳定性中的作用
A central hypothesis in ecology is that higher biodiversity increases ecosystem stability. Stability has two components: resistance — the ability to withstand disturbance — and resilience — the speed of recovery after a disturbance. Species-rich communities often show greater resistance to invasive species and can maintain functions like productivity during drought, because diverse assemblages contain a wider range of functional traits.
生态学的一个核心假说认为，更高的生物多样性会增强生态系统稳定性。稳定性包含两个部分：抵抗力（抵御干扰的能力）与恢复力（干扰后恢复的速度）。物种丰富的群落通常对入侵物种表现出更强的抵抗力，并能在干旱期间维持生产力等功能，因为多样化的组合包含了更广的功能性状谱。
The 'insurance hypothesis' suggests that redundancy among species with similar ecological roles buffers the ecosystem. If one species declines due to disease, another can compensate, maintaining nutrient cycles and energy flow. Controlled grassland experiments have demonstrated that plots with more plant species maintain more stable biomass from year to year.
‘保险假说’认为，具有相似生态角色的物种之间存在功能冗余，可为生态系统提供缓冲。若某个物种因病衰退，另一个物种可以弥补，从而维持养分循环和能量流动。受控的草原实验已证明，植物物种更多的样地，其年际生物量更为稳定。
Thus, the erosion of biodiversity not only represents a loss of life forms but also threatens the very life-support systems upon which humans depend. Sustaining biodiversity is therefore an investment in the long-term resilience of our planet.
因此，生物多样性的侵蚀不仅意味着生命形式的损失，更威胁到人类赖以生存的生命支持系统本身。维持生物多样性，就是对地球长期恢复力的一种投资。
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