📚 Experimental Design for Biodiversity Index | 生物多样性指数实验设计
Measuring biodiversity is one of the core practical skills in A-level biology and environmental science. Without a standardised method, counts taken in two different places cannot be compared fairly, and any conclusion about ecosystem health becomes unreliable. This guide sets out a complete, exam-ready experimental design for estimating species diversity in a terrestrial or aquatic habitat using quadrat sampling and Simpson's Index of Diversity. It covers the background theory, hypotheses, sampling strategy, apparatus, data recording, the calculation itself, statistical testing, control of variables, risk assessment, ethical issues and a final evaluation with the mistakes examiners see most often.
测量生物多样性是 A-level 生物与环境科学的核心实践技能之一。如果没有标准化的方法，两个地点的计数结果就无法公平比较，任何关于生态系统健康的结论都会变得不可靠。本指南提供一套完整、可直接用于考试的实验设计，用样方取样与辛普森多样性指数估算陆地或水生栖息地的物种多样性，内容涵盖背景理论、假设、取样策略、器材、数据记录、指数计算、统计检验、变量控制、风险评估、伦理问题，以及最后的调查评估与考试中最常见的失分点。
1. Background Concepts | 背景概念
Biodiversity is the variety of life forms within a given area, and it can be quantified at three levels: genetic diversity within a species, species diversity within a community, and ecosystem diversity across a whole landscape. Field investigations almost always measure species diversity, because it can be sampled within a reasonable time using standard apparatus and a repeatable protocol.
生物多样性是指特定区域内生命形式的多样性，可以在三个层次上量化：物种内部的遗传多样性、群落内部的物种多样性，以及整个景观层面的生态系统多样性。野外调查几乎总是测量物种多样性，因为它可以在合理时间内用标准器材和可重复的操作流程完成取样。
Species diversity has two components. Species richness is simply the number of different species present. Species evenness describes how similar the abundances of those species are. A lawn containing 20 species, where one grass makes up 95% of the cover, is ecologically less diverse than a meadow containing 15 species that are all present in similar numbers, even though the lawn has greater richness.
物种多样性由两个部分组成。物种丰富度就是出现的不同物种的数量。物种均匀度则描述这些物种个体数量的相似程度。一块含有 20 个物种、但其中一个禾草物种占 95% 覆盖度的草坪，在生态学意义上比一块含有 15 个物种、且各物种数量相近的草甸多样性更低，尽管草坪的丰富度更高。
A diversity index combines richness and evenness into a single number, which is why indices such as Simpson's and Shannon's are preferred to a bare species list when two habitats are compared. A single index value can be averaged, tested statistically and plotted against environmental variables.
多样性指数把丰富度与均匀度合并为一个数值，这正是比较两个栖息地时辛普森指数、香农指数等指数比单纯列出物种名录更受青睐的原因。一个指数值可以求平均、做统计检验，也可以与环境变量作图分析。
2. Hypotheses and Research Questions | 假设与研究问题
A well-designed investigation starts with a clear research question that names both the habitat and the comparison being made. Examples include: does species diversity differ between a grazed field and an ungrazed field? Does Simpson's Index of Diversity decrease with distance from a stream? Is diversity higher in the upper shore or the lower shore of a rocky beach? The question must be answerable with the apparatus and time available.
设计良好的调查从明确的研究问题开始，问题中要同时写明栖息地和所要进行的比较。例如：放牧地与未放牧地的物种多样性是否存在差异？辛普森多样性指数是否随距溪流距离的增加而下降？岩岸的高潮带与低潮带哪个多样性更高？研究问题必须能在现有器材和时间条件下得到回答。
ifference is due to chance. The alternative hypothesis (H₁) states that a significant difference does exist. The word significant refers strictly to the outcome of a statistical test at a chosen probability level, normally p = 0.05, meaning there is a less than 5% probability that the result arose by chance alone.
零假设（H₀）认为两个样点的平均多样性指数之间没有显著差异，观察到的任何差异都由随机因素造成。备择假设（H₁）认为确实存在显著差异。显著一词严格指在选定概率水平（通常 p = 0.05）下统计检验的结果，即结果仅由随机因素造成的概率低于 5%。
In this design the independent variable is the site or habitat type (for example grazed versus ungrazed, or upper versus lower shore), and the dependent variable is Simpson's Index of Diversity calculated from the quadrat data. Everything else that could change the measurement - quadrat size, time of day, season, observer, tidal state - is treated as a controlled variable.
在本设计中，自变量是地点或栖息地类型（例如放牧地与未放牧地，或高潮带与低潮带），因变量是由样方数据计算出的辛普森多样性指数。其他所有可能影响测量结果的因素——样方面积、一天中的时间、季节、观察者、潮位——都属于控制变量。
3. Habitat Choice and Sampling Strategy | 栖息地选择与取样策略
Choose a habitat that is safe, legally accessible and large enough to hold at least 10 to 20 quadrats. Terrestrial options include grassland, woodland floor, a hedgerow, a lawn or a rocky shore; aquatic options include a pond margin, a stream riffle or a rocky pool. Sampling one single 0.25 m² patch tells you almost nothing about the habitat as a whole, so a sampling strategy is needed to make the data representative.
选择安全、合法可进入且面积足够放置至少 10 至 20 个样方的栖息地。陆地选择包括草地、林地地被层、树篱、草坪或岩岸；水生选择包括池塘边缘、溪流浅滩或石质水潭。只取一个 0.25 m² 的小样方几乎无法代表整个栖息地，因此需要取样策略使数据具有代表性。
- Random sampling: quadrats are placed at randomly generated coordinates. This avoids bias, but may miss rare species or patchy features. 随机取样：样方放置在随机生成的坐标上，可避免偏差，但可能漏掉稀有物种或斑块状特征。
- Systematic sampling along a transect: quadrats are placed at regular intervals along a line, which is ideal for studying a gradient such as light intensity, moisture, altitude or trampling. 沿样线的系统取样：样方按固定间隔沿直线放置，最适合研究光照强度、湿度、海拔或践踏等梯度。
- Stratified sampling: the habitat is divided into recognisable zones (for example bare mud, mid shore and upper shore) and each zone is sampled randomly in proportion to its area. 分层取样：将栖息地划分为可识别的带（如裸泥带、中潮带、高潮带），按面积比例在各带内随机取样。
When two habitats are compared, use the same strategy, the same quadrat size, the same number of quadrats and, ideally, the same day and the same time of day at both sites. If a pilot survey shows that a quadrat contains fewer than about three species, either enlarge the quadrat or increase the number of quadrats.
比较两个栖息地时，应采用相同的取样策略、相同的样方面积、相同数量的样方，并尽量在同一天、同一时间进行。如果预调查发现一个样方中物种数少于约三种，则应扩大样方面积或增加样方数量。
4. Random Sampling in Practice | 随机取样的实际操作
True random sampling is harder than it looks. A reliable method is to lay two tape measures at right angles along the edges of the study area to form axes, then use a random number generator to produce pairs of coordinates. Place the quadrat with its bottom-left corner at each coordinate. Random numbers can be taken from a calculator, a spreadsheet function or printed random number tables.
真正的随机取样比看上去更难。可靠的方法是沿研究区边缘互相垂直地拉两条卷尺形成坐标轴，再用随机数生成器产生成对的坐标，把样方框的左下角放在每个坐标上。随机数可来自计算器、电子表格函数或印刷的随机数表。
Throwing a quadrat over the shoulder is sometimes used in school practicals, but it is not truly random because the throw itself is biased towards a particular distance and direction. Similarly, choosing patches that look typical introduces observer bias, since the observer unconsciously selects richer or tidier areas.
在学校实验中有时会把样方框从肩后抛出，但这并非真正随机，因为抛掷本身在距离和方向上带有偏差。同样，选择看起来典型的地块会引入观察者偏差，因为观察者会不自觉地挑选物种更丰富或更整齐的区域。
If a randomly generated point falls outside the habitat, on private land or on an unsafe surface, record the rejection, draw a new coordinate, and always report how many points were rejected. A high rejection rate is itself a limitation worth mentioning in the evaluation.
如果随机抽取的点落在栖息地之外、私人土地或不安全的位置，应记录该次弃用，重新抽取坐标，并报告一共弃用了多少个点。弃用率过高本身就是评估中值得提及的一项局限。
5. Apparatus and Materials | 器材与材料
The equipment list should be specific enough that another student could repeat the investigation exactly. For a terrestrial survey the standard kit includes the items below; aquatic and invertebrate surveys require additional equipment.
器材清单要足够具体，使另一位学生能够完全重复该调查。陆地调查的标准器材如下；水生与无脊椎动物调查还需要额外设备。
- quadrat for tall grassland; a point quadrat with 10 pins if percentage cover is required. 样方框，0.25 m²（50 cm × 50 cm），高草地可用 1 m² 样方框；若需测覆盖度可使用带 10 根探针的针点样方。
- Two tape measures, 20-30 m, for marking axes and transects. 两条 20–30 m 卷尺，用于标示坐标轴与样线。
- Random number generator, calculator or random number table. 随机数生成器、计算器或随机数表。
- dentification keys, hand lens (×10), camera or phone for photographs of unknown specimens. 检索表、手持放大镜（×10）、相机或手机，用于拍摄未知标本。
- Recording sheet on a clipboard, pencil, 30 cm ruler. 带夹板的记录表、铅笔、30 cm 直尺。
- Aquatic surveys: pond net or kick net (mesh 500-1000 µm), white sorting tray, plastic pipette, forceps, thermometer, pH meter or indicator paper, light meter. 水生调查：池塘网或踢网（网孔 500–1000 µm）、白色分拣盘、塑料滴管、镊子、温度计、pH 计或指示纸、光照计。
- Invertebrate surveys: pitfall traps with rain covers, sweep net, pooter. 无脊椎动物调查：带防雨盖的陷阱杯、扫网、吸虫管。
- Personal protective equipment: gloves, wellington boots, sun hat, first aid kit. 个人防护装备：手套、雨靴、遮阳帽、急救包。
If the same quadrats will be revisited in a later season, mark their corners with small pegs and record the coordinates so that the exact positions can be found again.
如果计划在另一个季节重访同样的样方，可用小木桩标记四角并记录坐标，以便再次找到完全相同的位置。
6. Recording Data and Species Identification
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