IB生物 生态学 样方 标记重捕 能量流动
IB 生物的生态学部分经常被当成背得最多的一章，实际考题集中在几个能算、能画、能判断的模型上。种群怎么估数、两个物种为什么不能长期共处、能量为什么只够支撑四到五个营养级，这些问题在 Paper 1 的选择题和 Paper 2 的数据题里年复一年出现。下面按 IBO 官方 subject guide 的顺序，把 B4.2、C4.1、C4.2 与 A4.2 四条线里的高频模型拆开，重点放在公式的适用条件与判断陷阱上，不堆结论。
Ecology in IB Biology carries a reputation for pure memorising, yet most marks sit on models you can count, draw or test. Estimating a population, explaining why two species cannot share one niche for long, and working out why food chains rarely run past four or five levels are the same questions that reappear in Paper 1 multiple choice and Paper 2 data analysis. What follows tracks the IBO subject guide and sticks to the conditions under which each model actually holds.
生态内容在新版考纲里的位置
IB DP 生物从 2023 年 8 月起改用新版考纲，2025 年 5 月第一次评估。原来独立的 Options 章节和 Paper 3 被取消，内容拆进 A 到 D 四个主题。生态学落在 Theme B 的 B4.1 适应环境与 B4.2 生态位，以及 Theme C 的 C4.1 种群与群落、C4.2 能量与物质转移。B4.2 占四小时，C4.1 与 C4.2 各五小时。考纲在这几条表述后面写明没有额外的 HL 内容，意思是 SL 与 HL 共用同一批知识点，差别落在总时数上: SL 150 小时，HL 240 小时。卷面上 SL 的 Paper 1 是一小时 30 分，其中 1A 为 30 道选择题，1B 为四道数据题共 25 分。Paper 2 一小时半 50 分，Section A 34 分的数据与短答在前，Section B 16 分长答二选一在后。
Since August 2023 the DP Biology guide has been taught in its current form, with first assessment in May 2025; the standalone Options chapters and Paper 3 disappeared, and their content moved into Themes A to D. Ecology now sits across B4.1 adaptation to environment and B4.2 ecological niches in Theme B, then C4.1 populations and communities with C4.2 transfers of energy and matter in Theme C, which together carry fourteen teaching hours. The syllabus states that these statements carry no additional higher level content, so HL candidates meet the same ideas with more hours (240 against 150) rather than extra sub-topics to learn.
生态位: 基础生态位与实际生态位
生态位描述一个物种在群落里怎么生活: 吃什么、在哪里取食、什么时候活动、能忍受什么温度与湿度。基础生态位是理论上能够占据的全部范围，实际生态位是有竞争者在场时真正占住的那一块。B4.2 要求用具体例子说明这两者的差距，实验室里把竞争者移走、看存活范围是否扩大，是最直接的证据形式。很多学生以为生态位就是栖息地，其实栖息地只是空间坐标，生态位还包括取食时间、食物颗粒大小、筑巢高度这类维度。同一片树林里三种莺可以在同一棵树的不同高度取食，视觉上共存，资源上并不重叠。写简答题时把维度写出来，比只写"它们在同一个地方生活"更容易拿到满分。
A niche describes how a species makes its living: what it eats, where it forages, when it is active, and which temperature and humidity range it tolerates. The fundamental niche is the full range available without rivals, while the realised niche is the smaller slice a species actually holds once competitors are present. Removing a competitor and watching whether the range widens is the cleanest evidence for that gap, and habitat alone is only the spatial coordinate, not the niche.
种群、群落与生态系统的层级
种群的考纲定义是同一物种、同一区域、能够正常繁殖的一群个体。区分同种的不同种群靠繁殖隔离，不必是地理隔离: 同一座山两侧的两个群体如果季节错开、无法交配，就是两个种群。群落是同一区域内所有种群的集合，生态系统则把群落与非生物环境一起算进来。C4.2.1 明确要求知道生态系统是开放系统，能量和物质都能进出；封闭系统只有能量能进出，这个对比句在选择题里出现过多次。学生最常把生态系统的边界画错，把一块草地的土壤和阳光漏掉，只画了草和兔子。
A population is defined as a group of organisms of the same species living in the same area and able to breed normally, and reproductive isolation, not geography, is what separates one population from another. A community gathers all the populations in an area, and an ecosystem adds the non-living surroundings to that community. The guide is explicit that ecosystems are open systems with both energy and matter crossing the boundary, which is exactly the contrast tested against a closed system.
随机样方与抽样误差
随机样方用于固着生物，比如草、苔藓、藤壶，因为它们跑不掉。取样点必须用随机数或网格坐标生成，不能随手挑"看起来典型"的地方，这一点直接决定数据能不能用。计数方式有两种: 体形较大、能分辨个体的直接数株数；覆盖成片、分不清个体的用百分覆盖率估计。抽样误差的定义是估计值与真实值之差，属于 Nature of Science 的考点，考纲不要求背标准差的公式，但要求会解释标准差大意味着样本间差异大、估计的可靠性低。常见的错误是只取一个样方就算平均值，标准差根本无从计算。
Quadrats suit sessile organisms such as grass, moss and barnacles, precisely because they cannot move away from the frame. Sampling points have to come from random numbers or a grid, never from a spot that simply looks typical, and large individuals are counted while dense mats are estimated as percentage cover. Sampling error is the gap between an estimate and the true value, and the standard deviation is there to be interpreted, not calculated from memory.
标记重捕法的四个假设
Lincoln 指数的形式是 M 乘 N 除以 R: M 是第一次捕捉并标记的个体数，N 是第二次重捕的总数，R 是其中带标记的个体数。公式简单，考点全在四个假设上。种群必须封闭，期间没有迁入迁出与出生死亡；标记不能脱落、不能被忽略；标记本身不能改变个体的存活率或被捕捉的概率；带标记的个体必须随机混回种群。这四个条件里任何一条破了，算出来的数字就系统性地偏大或偏小，讨论题往往只给一个场景让你判断哪条被破坏。取整方式也要注意，估算出小数点后的个体数没有生物学意义，写整数并说明是估计值。
The Lincoln index multiplies the number marked on the first visit by the total caught on the second, then divides by the number of marked individuals recaught. Its four assumptions carry the marks: a closed population, marks that neither fall off nor get overlooked, marks that do not alter survival or catchability, and marked individuals that mix back randomly. Break any one of them and the estimate drifts in a predictable direction, which is usually the whole point of the question.
环境容纳量与密度制约因素
环境容纳量是给定条件下环境能长期维持的种群规模上限，写成 K。密度无关因素比如霜冻、洪水、干旱，让种群数量上下波动，与个体密度无关。密度制约因素把种群推回 K: 资源竞争随个体增多而加剧，捕食者在猎物密集时更容易找到目标，病原体或害虫在拥挤种群中传播更快。这三个机制都属于负反馈，写简答时用"密度升高导致出生率下降或死亡率上升"这样的因果句最稳。很多学生会把"密度制约"直接等同于"食物不够"，其实捕食压力上升和疾病传播加快同样算密度制约，只写食物容易丢分。
Carrying capacity is the population size an environment can sustain over the long run, written as K. Density-independent factors such as frost, flooding or drought move numbers around regardless of how crowded the population is, whereas density-dependent factors push numbers back towards K. Competition for resources, rising predation pressure and faster spread of pathogens in crowded populations all act as negative feedback.
指数增长与 S 形曲线的判断
种群在资源充足、没有天敌时按指数方式增长，用纵轴取对数、横轴用普通刻度画半对数图，如果得到一条直线就说明是指数增长。资源有限时曲线转成 S 形，增长速度先加快、在 K 的一半附近最快，然后放缓并停在 K 附近。考纲里最容易踩的一条是 C4.1.7 的原文: lag phase 不被认为是 S 形生长的一部分，考试里凡是给出一段明显的缓慢起步期再让你解释的题，答案不是"个体在适应环境"。很多学生以为曲线前面总有一段 lag phase，因为他们在旧教材或别的科目里见过这个词，IB 生物这一条不吃这个说法。建模实验推荐酵母与浮萍，两者繁殖快、几周内就能画出完整曲线。
Populations grow exponentially while resources are plentiful, and plotting the counts on a logarithmic axis turns that growth into a straight line. Once resources bind, the curve becomes sigmoid: growth accelerates, peaks near half of K, then slows and levels off. The guide states that a lag phase is not expected as part of sigmoid growth, so a slow start is explained by something specific in the data rather than by adaptation.
六类种间关系与互利共生的三个实例
C4.1.11 列出六类种间关系: 食草、捕食、种间竞争、互利共生、寄生、致病，每一类都要配一个真实例子。答题时先写双方得失方向，再写机制，顺序颠倒很容易被扣分。互利共生的三个实例考纲点名要求: 豆科植物与根瘤菌，植物得到含氮化合物、细菌得到糖类；兰科植物与菌根真菌，真菌帮植物吸收矿物质、植物提供有机物；硬珊瑚与虫黄藻，珊瑚提供庇护与二氧化碳，藻类提供光合产物。写这三例必须把双方收益写清楚，"互相帮助"这种表述拿不到分。化感作用与抗生素分泌也要各配一例，它们说明一个物种可以用化学物质改变邻居的生存条件。
Six interspecific relationships are examined: herbivory, predation, interspecific competition, mutualism, parasitism and pathogenicity, each with a named example. Every answer should state which partner gains and which loses before describing the mechanism, because the direction of benefit is part of the mark. Mutualism has three required examples, and each one needs both benefits spelled out rather than described vaguely as helping each other.
竞争只能被指示而不能被证明
考纲明确写竞争只能被 indicated，不能被 proved，因为两个物种数量此消彼长还可能由别的因素造成。研究竞争有三条路径: 做实验，把可能的原因隔离出来；在自然条件下随机取样观测分布与数量；把其中一个物种移走，看另一个是否扩张。第三条的证据力最强，但野外操作常涉及伦理与许可限制，写答案时可以提到这一点。学生最常把相关当因果，看到两个物种从不同时出现就直接下结论说它们竞争，其实还可能是捕食者偏向于吃其中一种，或两者的土壤湿度需求不同。
Competition can only be indicated, never proved, because a decline in one species alongside a rise in another has more than one possible cause. Three routes exist: controlled experiments that isolate a cause, random sampling of distributions in the field, and removal of one species to see whether the other expands. Removal trials give the strongest evidence, though they carry ethical and licensing constraints in the field.
卡方检验判断两物种是否共现
判断两个物种是否倾向出现在同一批样方里，用卡方检验。数据排成 2 乘 2 的表格: 两行是两个物种出现与不出现，两列同样是出现与不出现，自由度是 1。5% 显著性水平的临界值是 3.84，算出的卡方值高于它就拒绝"出现与否相互独立"的假设，说明两者要么互相吸引要么互相排斥。这一步最容易出错的地方是期望频数不能太小，某些格子的期望值低于 5 时检验结果不可靠，需要扩大样本或合并分类。写结论要把方向说清楚: 共现倾向还是回避倾向，卡方值本身只说"有关联"。
A chi-squared test asks whether two species turn up in the same quadrats more or less often than chance would predict. The data go into a two by two table of presence and absence, giving one degree of freedom, and the 5 per cent critical value is 3.84. A calculated value above that rejects independence, but the test by itself never tells you whether the association is attraction or avoidance, so the direction has to come from the counts.
能量的单向流动与营养级数目
能量在生态系统里单向流动，物质则循环使用，这个区别是 C4.2 的核心。太阳能是主要能量来源，洞穴生态系统与超过光线穿透深度的深海是明确列出的例外。能量每经过一个营养级都递减，呼吸作用产生的热无法被下一级再利用，所以食物链通常不超过四到五个营养级。往上走，个体数量或个体体积下降，总生物量下降，但单位质量的能量含量并不降低，这个细节常出现在判断题里。初级生产的单位是每平方米每年多少克碳，次级生产一定低于初级生产。
Energy flows one way through an ecosystem while matter cycles, and that distinction is the spine of C4.2. Sunlight is the main energy source, with cave ecosystems and deep water below the light penetration depth listed as exceptions. Each transfer loses energy as heat from respiration, which caps food chains at four or five levels, and biomass falls towards the top even though the energy content per unit mass does not.
初级生产、次级生产与碳源碳汇
碳循环图在考纲里只需要三条通路: 光合作用把二氧化碳固定成有机物，摄食把碳沿着食物链传递，呼吸把碳放回大气。分解者同样关键，只是考纲写明不需要知道氮循环的细节，这一条可以省下不少背书时间。光合速率大于呼吸速率时，该生态系统净吸收碳，就是碳汇；反过来是碳源。基林曲线记录的是大气二氧化碳浓度的长期变化，由 Mauna Loa 观测站记录、NOAA 与 Scripps 两家机构维护，曲线有年度锯齿: 北半球生长季在 5 月前后把浓度压到低点，9 到 10 月呼吸占上风时回到高点。锯齿之上是持续上升的长期趋势。
Only three pathways are required on the carbon cycle diagram: photosynthesis fixing carbon dioxide, feeding moving carbon along food chains, and respiration returning it to the atmosphere. Decomposers matter throughout, yet the guide states that details of the nitrogen cycle are not needed. When photosynthesis outruns respiration an ecosystem is a net carbon sink, and the Keeling curve from Mauna Loa, maintained by NOAA and Scripps, shows the annual sawtooth riding on a long upward trend.
生物多样性三层与保育手段
生物多样性分生态系统、物种与遗传三个层次，三者都要能在题目里各举一例。判断生物多样性下降必须有可核查的重复调查证据，IPBES 这类评估机构的作用就是把长期数据汇总起来。人为原因包括过度捕猎与开采、城市化、为农业清林导致的栖息地丧失，以及随全球运输扩散的污染、病虫害与入侵种。保育手段要分就地与迁地: 就地保护是保护区管理与退化生态系统恢复，迁地保护是动物园、植物园、种子库与组织库，EDGE 项目的排序逻辑是把演化独特性与濒危程度一起考虑。Simpson 倒数指数、Lincoln 指数、卡方检验与 t 检验并列在技能清单里，只要求会用，不要求背公式细节。复习安排上，三周足够: 第一周把 C4.1 的抽样与估算题刷熟，第二周攻 C4.2 的能量与碳循环，第三周用真题把简答的因果句练成固定表达。
Biodiversity has three levels, ecosystem, species and genetic, and each needs its own example. Claims about decline require repeatable survey evidence of the kind bodies such as IPBES assemble from long-term data. Conservation splits into protecting habitats in place and maintaining breeding populations away from them, including zoos, botanic gardens, seed banks and tissue banks, while the EDGE approach ranks species by evolutionary distinctiveness together with extinction risk.
牛津AQA国际GCSE生物?OxfordAQA International GCSE Biology (9201): Onl?进口原版¥399.0📱 去京东购买京东精选
需要一对一辅导？Need One-on-One Tutoring?
A-Level / GCSE / IB / KS2-KS3 全科辅导
16621398022 同微信
Visit aleveler.com
或截图后用「扫一扫 → 相册」选择本图