OCR A-Level Biology Biodiversity考点全解析

OCR A-Level Biology Biodiversity考点全解析

Biodiversity complete guide: key concepts, Simpson's Index, sampling methods & exam tips | 生物多样性完整解析

What Is Biodiversity? 什么是生物多样性？

Biodiversity（生物多样性）refers to the variety of living organisms on Earth — from microorganisms to mammals. It is a core topic in OCR A-Level Biology Module 4: Biodiversity, Evolution and Disease. Students must understand biodiversity at different levels and learn to measure it quantitatively.

生物多样性指地球上生物体的多样性，是OCR A-Level生物学模块4的核心主题。学生需要理解不同层次的生物多样性，并学会定量测量。

Three Levels of Biodiversity 三个层次

Habitat biodiversity（栖息地多样性）: the range of different habitats within an ecosystem. A woodland contains canopy, shrub, field, ground, and soil layers — each supporting distinct communities. High habitat diversity correlates with high species diversity.

栖息地多样性指一个生态系统内不同栖息地的范围。林地包含冠层、灌木层、草本层、地面层和土壤层，各自支撑特有生物群落。

Species biodiversity（物种多样性）: combines species richness（物种丰富度，number of species）and species evenness（物种均匀度，distribution of individuals among species）. A community dominated by one species has high richness but low evenness.

物种多样性包含物种丰富度（物种数量）和物种均匀度（个体分布均匀程度）。一个物种主导的群落丰富度高但均匀度低。

Genetic biodiversity（遗传多样性）: the variety of alleles in a gene pool. Higher genetic diversity increases a population's ability to adapt and resist disease. Populations that have passed through a genetic bottleneck are more vulnerable to extinction.

遗传多样性指基因库中等位基因的多样性。遗传多样性越高，种群适应环境和抵御疾病的能力越强。经过遗传瓶颈的种群更易灭绝。

Simpson's Index of Diversity 辛普森多样性指数

OCR requires students to calculate Simpson's Index (D):

D = 1 − Σ[n(n − 1) / N(N − 1)]

Where n = individuals of a species, N = total individuals. D ranges from 0 (no diversity) to 1 (infinite diversity). A higher D reflects both greater richness and evenness.

OCR考试要求计算辛普森指数D = 1 − Σ[n(n − 1) / N(N − 1)]。D值从0到1，D越高表示多样性越大。它同时反映丰富度和均匀度。

Exam tip 考试技巧：When explaining a low D value, mention both low species count (richness) AND dominance by few species (evenness). For large samples, D ≈ 1 − Σ(n/N)².

Factors Threatening Biodiversity 威胁因素

Habitat destruction（栖息地破坏）: deforestation, urbanisation, and agriculture remove entire ecosystems. Tropical rainforests host over 50% of terrestrial species.

Climate change（气候变化）: rising temperatures shift geographic ranges. Coral bleaching caused by warming oceans destroys biodiverse marine habitats.

Overexploitation（过度开发）: unsustainable hunting and fishing — the collapse of North Atlantic cod stocks is a classic OCR case study.

Invasive species（入侵物种）: non-native organisms outcompete natives — grey squirrels displacing red squirrels in the UK is a key example.

Pollution（污染）: agricultural runoff causes eutrophication（富营养化）. Pesticides accumulate via bioaccumulation and biomagnification up food chains.

人类活动是生物多样性丧失的主要驱动力，包括栖息地破坏、气候变化、过度开发、入侵物种和污染五大因素。

Sampling Techniques 采样技术

Random sampling（随机采样）: uses random coordinates to eliminate observer bias — essential for statistically valid estimates.

Systematic sampling（系统采样）: samples at regular intervals along a transect, ideal for studying zonation across environmental gradients like sand dunes.

Quadrats（样方）: square frames (typically 0.5m×0.5m) for counting plants or slow-moving organisms. Provides data on percentage cover, frequency, or density.

Mark-release-recapture（标记-释放-重捕法）: for motile organisms. Lincoln Index: N = (n₁ × n₂) / n₃. Key assumptions: no migration, no births/deaths, marks remain, random mixing. 关键假设：无迁入迁出、无生死变化、标记不丢失、标记个体随机混合。

Conservation Strategies 保护策略

In-situ conservation（就地保护）: protects species in natural habitats — National Parks, SSSIs (Sites of Special Scientific Interest), Marine Protected Areas.

Ex-situ conservation（迁地保护）: removes organisms for protection — seed banks, zoos, botanical gardens, captive breeding programmes. 迁地保护包括种子库、动物园、植物园和圈养繁殖计划。

CITES（濒危野生动植物种国际贸易公约）regulates trade in endangered species. The IUCN Red List classifies extinction risk from Least Concern to Extinct.

The Rio Convention on Biological Diversity (1992) established three objectives: conservation, sustainable use, and fair benefit-sharing. 《里约生物多样性公约》确立了保护、可持续利用和公平分享惠益三大目标。

OCR Exam Focus 考试重点

Command words 指令词："Describe" → state observations. "Explain" → give biological reasons. "Evaluate" → discuss both sides and conclude. "Suggest" → apply knowledge to new contexts.

Common pitfalls 常见失分点：(1) Confusing species richness with evenness. (2) Forgetting Simpson's Index covers both. (3) Omitting Lincoln Index assumptions. (4) Mixing up bioaccumulation vs biomagnification. (5) Not linking conservation strategies to specific threats.

常见失分点：混淆丰富度与均匀度、忽略辛普森指数双重属性、遗漏林肯指数假设、混淆生物累积与生物放大、未将保护策略与威胁挂钩。

Practical endorsement 实验技能：Be ready to design ecological sampling investigations — risk assessment, apparatus selection, and statistical analysis (Spearman's rank, chi-squared). 准备好设计生态采样调查——风险评估、器材选择与统计分析。

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