Why Does Biodiversity Matter? | 为什么生物多样性至关重要

📚 Why Does Biodiversity Matter? | 为什么生物多样性至关重要

Biodiversity describes the variety of living organisms on Earth, from genes within a population to species within a community and ecosystems across a landscape. It is not a luxury but a functional requirement of healthy ecosystems; losing biodiversity destabilises food webs, nutrient cycles and the services that human societies depend on. In A-level Biology, biodiversity is both a measurable concept and a basis for evaluating conservation decisions.

生物多样性描述地球上生物的多样性，涵盖种群内的基因、群落中的物种以及景观中的生态系统。它并非可有可无，而是健康生态系统正常运作的必要条件；丧失生物多样性会破坏食物网、养分循环以及人类社会所依赖的生态服务。在A-level生物中，生物多样性既是一个可测量的概念，也是评估保护决策的基础。

1. Defining Biodiversity | 生物多样性的定义

Biodiversity, or biological diversity, is the variety of living organisms in a given area. It is usually described at three levels: genetic diversity within a species, species diversity within a community and ecosystem diversity across a landscape. In the Cambridge A-level specification, biodiversity is often quantified by species richness and species diversity indices.

生物多样性指某一地区内生物的多样性。通常从三个层次描述：物种内的遗传多样性、群落内的物种多样性以及景观范围内的生态系统多样性。在剑桥A-level大纲中，生物多样性常用物种丰富度和物种多样性指数来量化。

High biodiversity does not simply mean a large number of species. A community in which one species dominates has lower diversity than a community with the same number of species but similar abundances. This distinction matters because evenness influences ecosystem functions and stability.

高生物多样性并不只意味着物种数量多。如果一个群落中某一物种占绝对优势，其多样性低于物种数量相同但各物种数量相近的群落。这种区别很重要，因为均匀度会影响生态系统功能和稳定性。

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2. Levels of Biodiversity: Genes, Species and Ecosystems | 生物多样性的层次：基因、物种与生态系统

Genetic diversity is the total number of different alleles in all individuals of a species or population. It provides the raw material for adaptation and evolution. Species diversity combines species richness and species evenness. Ecosystem diversity refers to the variety of habitats, communities and ecological processes in the biosphere.

遗传多样性指一个物种或种群所有个体中不同等位基因的总数，为适应和进化提供原材料。物种多样性包括物种丰富度和物种均匀度。生态系统多样性指生物圈中栖息地、群落和生态过程的多样性。

All three levels are interconnected. For example, habitat loss reduces ecosystem diversity, which fragments populations, reduces gene flow and lowers genetic diversity. Conservation therefore must operate at multiple levels.

这三个层次相互关联。例如，栖息地丧失会降低生态系统多样性，使种群片段化，减少基因流动并降低遗传多样性。因此保护工作必须在多个层次上进行。

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3. Measuring Species Diversity: Species Richness and Simpson’s Index | 物种多样性的测量：物种丰富度与辛普森指数

Species richness (S) is the simplest measure: the number of different species present in a sample. It is easy to obtain but ignores population sizes and therefore can be misleading.

物种丰富度（S）是最简单的指标，即样本中存在的不同物种数量。它易于获得，但忽略了种群大小，因此可能具有误导性。

Simpson’s index of diversity (D) accounts for both richness and evenness.

D = 1 – Σ (n/N)²

Here n is the total number of organisms of a particular species and N is the total number of organisms of all species. D varies from 0 (very low diversity) to 1 (very high diversity).

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。D 值从 0（多样性极低）到 1（多样性极高）变化。

For example, if a sample contains 20 individuals of species A and 5 of species B, N = 25. Then Σ (n/N)² = (20/25)² + (5/25)² = 0.64 + 0.04 = 0.68, so D = 1 – 0.68 = 0.32.

例如，如果样本包含物种 A 20 个个体和物种 B 5 个个体，则 N = 25。那么 Σ (n/N)² = (20/25)² + (5/25)² = 0.64 + 0.04 = 0.68，因此 D = 1 – 0.68 = 0.32。

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4. Ecosystem Services Provided by Biodiversity | 生物多样性提供的生态系统服务

Biodiversity underpins ecosystem services, the benefits humans obtain from ecosystems. These are often grouped into provisioning services (food, fresh water, timber, fibre, medicines), regulating services (climate, flood, disease and water purification), supporting services (nutrient cycling, soil formation, primary production) and cultural services (recreation, education, aesthetics).

生物多样性支撑着生态系统服务，即人类从生态系统中获得的惠益。这些服务通常分为供给服务（食物、淡水、木材、纤维、药物）、调节服务（气候、洪水、疾病和水质净化）、支持服务（养分循环、土壤形成、初级生产）和文化服务（娱乐、教育、美学）。

A loss of biodiversity does not merely remove a few species; it weakens the entire delivery of these services. For example, overfishing can collapse fish stocks, reducing food provision and damaging coastal livelihoods.

生物多样性的丧失不仅仅是消失几个物种，它会削弱整个生态系统服务的提供。例如，过度捕捞可能导致鱼类种群崩溃，减少食物供给并损害沿海生计。

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5. Nutrient Cycling and Soil Formation | 养分循环与土壤形成

Decomposers such as saprobionts, including bacteria and fungi, secrete enzymes to break down dead organic matter, releasing ammonium ions, phosphate and other minerals into the soil. Detritivores such as earthworms and woodlice fragment organic material, increasing the surface area for microbial action.

腐生细菌和真菌等分解者分泌酶来分解死亡的有机物，将铵离子、磷酸盐和其他矿物质释放到土壤中。蚯蚓和木虱等食碎屑动物将有机物质破碎，增加微生物作用的表面积。

Nitrogen-fixing bacteria convert atmospheric nitrogen (N₂) into ammonia, while nitrifying bacteria oxidise ammonium to nitrate. A diverse soil community ensures that nutrients are recycled efficiently, maintaining soil fertility for primary producers.

固氮细菌将大气中的氮（N₂）转化为氨，硝化细菌则将铵氧化为硝酸盐。多样的土壤群落确保养分高效循环，维持初级生产者的土壤肥力。

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6. Pollination and Seed Dispersal | 传粉与种子传播

Around 75% of globally important food crops depend at least partly on animal pollination by bees, flies, butterflies, birds and bats. Declines in wild pollinator diversity reduce fruit set, seed quality and crop yield, especially in plants that cannot self-pollinate.

全球约75%的重要粮食作物至少部分依赖蜜蜂、蝇类、蝴蝶、鸟类和蝙蝠等动物传粉。野生传粉者多样性的下降会降低坐果率、种子质量和作物产量，尤其是无法自花授粉的植物。

Seed dispersal by animals also maintains plant population structure and enables colonisation of new habitats. When large fruit-eating animals disappear, tree species may fail to regenerate, altering forest composition and reducing biodiversity further.

动物传播种子还能维持植物种群结构并使其能够在新栖息地定殖。当大型食果动物消失时，树木可能无法更新，改变森林组成并进一步降低生物多样性。

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7. Climate Regulation and Carbon Storage | 气候调节与碳储存

Forests, peatlands, grasslands and oceans store carbon in living biomass and soil organic matter. Photosynthesis by producers removes carbon dioxide from the atmosphere, converting it into carbohydrates. Ecosystems with high plant diversity often show higher carbon sequestration because different species use resources in complementary

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