IB生物 生态学 生态位 种群 能量流动
生态学在 IB 生物里不是靠背名词拿分的板块。2025 年 5 月首次评估的新版指南把旧版的 Options 与 Paper 3 一起取消，生态内容重新排进 Theme B 的 B4.1 适应环境、B4.2 生态位和 Theme C 的 C4.1 种群与群落、C4.2 能量与物质的传递，四节都归在生态系统这个组织层级下。C4.1 与 C4.2 各排 5 小时教学时间，条目末尾都注明没有额外的 HL 内容，SL 与 HL 学的是同一批知识点，差别在教学时数上，SL 的 Theme C 共 31 小时，HL 是 48 小时。技能清单把 Lincoln 指数、Simpson 倒数指数、卡方检验与 t 检验并列，处理野外数据的能力成了明确的拿分点。下面按考纲条目顺序把种群估计、种间关系、能量流动与物质循环串成一条线，每条都写清对应的习题形态与要做的动作。
Ecology in IB Biology rewards data handling far more than vocabulary recall. The guide first assessed in May 2025 removed the old Options and Paper 3, and placed the content in B4.1 adaptation to environment, B4.2 ecological niches, C4.1 populations and communities, and C4.2 transfers of energy and matter; C4.1 and C4.2 each carry five teaching hours and state that they contain no additional higher level material, so the difference between SL and HL is time rather than content. Work through this article in syllabus order, and check each point against the official IBO guide rather than a summary.
2025 版考纲里生态内容的位置
旧版指南把生态与保护放在 Paper 3 的一个 Option 里，学校在四个 Option 中选一个教。新版取消 Options 与 Paper 3 之后这部分内容没有消失，而是按组织层级重新排进四个主题。生态主题落在 Theme B 的 B4.1 与 B4.2，以及 Theme C 的 C4.1 与 C4.2，考点集中在四件事上：种群规模怎么估、物种之间怎么互相制约、能量怎么走、物质怎么循环。SL 的校外考试共 3 小时，Paper 1 满分 55 分（1A 30 分选择题加 1B 25 分数据题）占 36%，Paper 2 满分 50 分（A 部分 34 分加 B 部分 16 分）占 44%，其余 20% 是校内科学探究，HL 的卷面结构相同。生态题出现在 1B 与 2A 的数据位置上，纯记忆题比例不高，复习重心要放在读图表与算估计值上。
Under the older guide, ecology and conservation were taught as one optional Paper 3 unit chosen from four. The current guide keeps the same material but redistributes it across themes and organisation levels, with B4.1 and B4.2 inside Form and Function and C4.1 and C4.2 inside Interaction and Interdependence, covering population estimation, species interactions, energy flow and nutrient cycling. SL sits three hours of external papers, with Paper 1 worth 55 marks at 36 per cent and Paper 2 worth 50 marks at 44 per cent, while HL writes two hours for Paper 1 and two and a half hours for Paper 2; ecology tends to land in the data-based slots rather than in recall questions.
生态位是角色，不是住址
考纲把生态位定义为一个物种在生态系统中的角色，包含影响它生长、存活与繁殖的生物与非生物相互作用，也包含它怎样获得食物。很多学生以为生态位就是住在哪里，那是栖息地，栖息地只是生态位里的一小块。B4.2.12 把两个概念分开：基础生态位由适应特征与耐受极限决定，是理想条件下的潜力范围，实现生态位是与其他物种竞争之后实际占据的那一部分。两者的差距通常来自竞争，而不是来自温度、光照这类物理限制。B4.2.13 把竞争排斥的结果写得很具体，一种被淘汰出局，或者两个物种各自被限制在基础生态位的一部分内。
An ecological niche is the role a species plays in an ecosystem, defined by the biotic and abiotic interactions that shape its growth, survival and reproduction, including how it obtains food. Habitat is the place an organism lives, which is only one component of the niche, and conflating the two loses marks in extended answers. The fundamental niche is the potential range set by adaptations and tolerance limits, while the realized niche is the narrower part a species actually holds once competition is present; competitive exclusion then either removes one species or restricts both to part of their fundamental niche.
种群、群落与生态系统的分层
种群的定义包含三个条件：同一物种、同一区域、正常能够相互繁殖。考纲用繁殖隔离区分同一物种的不同种群，所以同一片林子里两个互不往来的同种群体算两个种群。学生最常把群落写成这一带的所有动物，考纲的口径是一个区域内全部相互作用的生物，植物、动物、真菌与细菌都算进去。生态系统在群落之外加上非生物环境，以及生物与环境之间的相互作用。生物圈是所有生态系统的总和，也就是地球上被生物占据的那一层。这类层级题在 Paper 1A 里通常给四个描述，判断依据是有几种物种、环境有没有被算进去，与区域面积无关。
A population is a group of organisms of the same species living in one area that normally interbreed, and reproductive isolation is the criterion the syllabus uses to separate one population from another. A community contains every interacting organism in that area, plants, animals, fungi and bacteria included, while an ecosystem adds the abiotic environment and the interactions between organisms and it. The biosphere is the sum of all ecosystems, and multiple-choice items on this chain are usually solved by asking whether the description covers more than one species and whether the physical environment is included.
随机取样、样方与标准差
C4.1.2 先解释为什么要估计而不是逐个计数：移动快、密度低、藏在土壤里或夜间活动的生物根本数不完。取样必须随机，考纲把随机取样的代价写得很直白，估计值与真实值之间的差就是抽样误差。C4.1.3 针对固着生活的生物，用随机样方数个体，或者用百分覆盖率记录草地、苔藓与地衣这类分不出个体的生物。常见的错误是沿着小路或林缘选点，那里的光照与人为干扰和林地内部不同，估计值会系统性偏高。估计总个体数的算法是每样方平均个体数乘以总面积再除以单个样方面积。技能部分要求说明平均数的标准差代表什么，它衡量数据的离散程度，也说明种群在区内分布得是否均匀。
Counting every individual is impractical for organisms that move quickly, live at low density or hide in soil, and the guide states plainly that random sampling produces a sampling error, the gap between the estimate and the true population size. Random quadrats suit sessile organisms and can be used either to count individuals or to record percentage cover for grasses, mosses and lichens, while sampling along a path or at a woodland edge biases the estimate upwards because light and disturbance differ from the interior. Total population size is estimated as the mean per quadrat multiplied by total area divided by quadrat area, and the standard deviation of that mean describes how evenly the population is spread; the formula itself does not need to be memorised.
Lincoln 指数与标记重捕的四条假设
C4.1.4 用标记重捕法处理移动生物，估计值等于初次捕捉并标记的个体数 M 乘以第二次重捕的个体总数 N，再除以其中带标记的个体数 R。一个课堂例子是第一次捕到并标记 40 只，第二次重捕 50 只，其中 8 只带标记，估计种群为 40 乘 50 除以 8，等于 250 只。这一步最容易做错的地方是把 N 与 R 写反，把带标记的重捕数当成重捕总数。考纲要求理解方法的假设，第一条是种群封闭，两次取样之间没有迁入迁出、出生或死亡。第二条是标记既不丢失也不被漏看，标记过程不改变个体的存活率与被再次捕到的概率。第三条是被标记个体要在两次取样之间充分混回种群，否则第二次重捕会高估带标记个体的比例。标记丢失或被漏看会让 R 偏小，估计值随之偏大，这是野外估计普遍偏高的常见原因。
Capture-mark-release-recapture is the syllabus method for motile organisms, and the Lincoln index estimates population size as M times N divided by R, with M the number marked at first capture, N the total number recaptured and R the number of marked individuals in that second sample. A worked example: mark 40, recapture 50, find 8 marked, so the estimate is 250. The method only holds when the population is closed, marks are neither lost nor overlooked, marking does not change survival or catchability, and marked individuals mix back randomly; estimates that come out too high usually trace back to lost or missed marks, which shrink R.
环境容纳量与密度制约的负反馈
C4.1.5 对容纳量的要求很简单：在资源有限的情况下，一个环境能长期支撑的种群规模。限制资源可以举食物、水、空间、筑巢地点与光照，不同生态系统的限制因素并不一样。C4.1.6 把两类因素分开，密度无关的因素让数量上下波动，干旱、霜冻与洪水都属于这一类。密度制约的因素倾向于把种群推回容纳量附近，数量越多作用越强。考纲点名的三个机制是资源竞争加剧、捕食风险随密度上升，以及病原体或害虫在密集种群里的传播加快。很多学生以为捕食只会压低数量，考纲的写法是捕食风险随密度上升，它起的是负反馈调节作用，把种群拉回容纳量而不是消灭种群。野外案例里两类因素同时存在，考纲要求在具体生态系统里至少研究一个案例。
Carrying capacity only needs a working definition: the population size an environment can sustain over time when resources are limited, with food, water, space, nesting sites and light as the usual limiting resources. Density-independent factors such as drought, frost and flooding make numbers fluctuate, whereas density-dependent factors push the population back towards that ceiling, and the guide names three mechanisms: sharper competition for resources, a higher risk of predation, and faster transfer of pathogens or pests in crowded populations. In real case studies both kinds of factor operate at once, which is why at least one case study inside a named ecosystem is required.
指数增长、S 形曲线与半对数图
C4.1.7 要求用至少一个生态系统的案例研究种群增长曲线，并解释初始阶段为什么接近指数增长：资源充足、捕食与疾病压力小，出生率远高于死亡率。数量上升之后，密度制约因素开始起作用，曲线转为 S 形，在容纳量附近趋于平缓。考纲在 S 形增长这一条里特意写明，滞后阶段不作为 S 形曲线的一部分，很多学生以为开头那一段平缓就是滞后阶段，卷面上这样写会被判错。技能要求把种群数据画成纵轴对数、横轴普通刻度的半对数图，得到直线就说明该阶段符合指数增长模型。C4.1.8 要求自己收集数据做建模，酵母与浮萍是推荐材料，几天就能画出完整曲线。
Population growth approaches exponential form early on because resources are ample and predation and disease pressure is low, so births far outnumber deaths. Once numbers rise, density-dependent factors take over, the curve becomes sigmoid and levels off near carrying capacity, and the guide adds a detail worth memorising: a lag phase is not expected as part of sigmoid growth. To test whether an early phase really is exponential, plot population size on a logarithmic axis against linear time and look for a straight line, and if you collect your own data, yeast and duckweed are the recommended organisms.
种间关系的六个类别与三个共生实例
C4.1.11 要求把种间关系分成六类：食草、捕食、种间竞争、互利共生、寄生与致病，每一类至少配一个例子。分类依据是双方各自的得失，食草与捕食一方受益一方受损，种间竞争双方都受损，互利共生双方受益，寄生与致病一方受益而寄主受损，区别在于致病生物通常在寄主体内生活并引发疾病症状。C4.1.12 点名三个互利共生实例，每个都要写清双方得到什么：豆科植物根部的根瘤菌固定大气中的氮，兰花科的菌根真菌扩大水分与矿质离子的吸收面积，硬珊瑚体内的虫黄藻通过光合作用向珊瑚提供碳源。考纲允许答题时写俗名或学名，但只写它们互相帮助拿不到分，要给机制。C4.1.16 要求用一个真实案例说明捕食者与被捕食者的数量变化，这类数据题一般给两条曲线，问相位差与密度制约的证据。
Interspecific relationships fall into six categories: herbivory, predation, interspecific competition, mutualism, parasitism and pathogenicity, each with at least one named example. The classification follows the balance of benefit, since predation and herbivory favour one side at the expense of the other, competition costs both species, mutualism benefits both, and parasitism or pathogenicity benefits one while damaging the host. For mutualism the syllabus names root nodules in legumes, mycorrhizae in orchids and zooxanthellae in hard corals, and a predator-prey case study usually asks you to read two population curves and comment on the time lag and the density-dependent control.
卡方检验判断两物种是否一起出现
C4.1.14 先给出判断逻辑：一个物种在另一个物种缺席时表现更好，只能说明存在种间竞争的迹象，不能证明竞争就是原因。考纲列出三类研究路径，实验室实验、随机取样的野外观测，以及移走一个物种的野外操控实验。C4.1.15 要求用卡方检验处理两个物种在多个取样点出现与不出现的记录，看它们的分布是否存在关联。做法是把有与无整理成两行两列，算出卡方值之后查自由度 1 的临界值，5% 显著性水平下是 3.84。错得最多的是把卡方值算出来就下结论，既不看自由度也不与临界值比较。检验结果显著地不共现只是与竞争假设一致，还要结合生态位与资源数据解释，这一点在长答题的结论句里经常被漏掉。
The guide is careful about wording here: a species doing better when a competitor is absent indicates interspecific competition but does not prove it, so it lists three research routes, namely laboratory experiments, field observation by random sampling, and field manipulation by removing one species. The chi-squared test is applied to the presence and absence of two species across several sampling sites, arranged as a two-by-two table with one degree of freedom and a critical value of 3.84 at the five per cent level. A significant result is consistent with competition rather than proof of it, which is why the conclusion of a long answer has to bring in niche and resource data as well.
能量单向流动，物质反复循环
C4.2.1 把生态系统定义为开放系统，能量与物质都能进入和离开，封闭系统里只有能量能穿过边界。C4.2.2 指出太阳光是维持绝大多数生态系统的能量来源，洞穴生态系统与超出光线穿透深度的深海是考纲点明的例外。能量沿食物链单向传递，每一级都有大量能量以热的形式散失，C4.2.13 把原因落在呼吸作用上，化学能转成 ATP 与热的过程中传递效率不可能达到百分之百。很多学生以为能量会像物质一样循环，考纲的口径是热不能被生物重新用来做功，生态系统必须持续获得外部能量输入。C4.2.12 说明相邻营养级之间可利用能量递减，分解者与食碎屑者通常不画进食物链，但它们在能量转化里占重要位置。C4.2.14 由此解释营养级数目的限制，越往上个体越少或越小，生物量越少，单位质量的能量含量并不降低。
Ecosystems are open systems through which both energy and matter pass, and sunlight is the principal energy source for most of them, with caves and the deep ocean below the light penetration layer given as exceptions. Energy travels in one direction along a food chain, and the guide attributes the losses to respiration, because converting chemical energy into ATP and heat can never be fully efficient and heat cannot be reused by organisms to do biological work. That steady loss explains the limit on trophic levels, since each successive stage holds fewer or smaller organisms and less biomass, although energy content per unit mass does not fall.
初级生产、次级生产与碳源碳汇
C4.2.15 把初级生产定义为自养生物在生物量中积累碳化合物，单位是每单位面积每单位时间的碳质量，通常写成每平方米每年多少克。C4.2.16 说明次级生产必然低于初级生产，因为异养生物在呼吸中把一部分碳化合物转成了二氧化碳与水。C4.2.17 只要求画三条通路的碳循环图，光合作用、摄食与呼吸，把碳在生物与大气之间往返的过程连起来。C4.2.18 给出碳源与碳汇的判据，光合作用超过呼吸作用是净吸收二氧化碳，反过来就是净释放。C4.2.20 要求分析基林曲线，既要看每年 5 月前后见顶、9 到 10 月见底的季节波动，又要看长期上升趋势，这组数据由 Mauna Loa 观测站持续记录，由 NOAA 与 Scripps 维护。常见的错误是花时间背氮循环每一步，考纲写明不需要知道氮循环与其他营养循环的细节，只需理解所有元素都在生态系统中循环、分解者起关键作用。
Primary production is the accumulation of carbon compounds in biomass by autotrophs, measured as mass of carbon per unit area per unit time, usually grams per square metre per year, and biomes differ widely in that capacity. Secondary production has to be lower because heterotrophs release part of those carbon compounds as carbon dioxide and water during respiration, and a carbon cycle diagram only needs the three routes of photosynthesis, feeding and respiration. The Keeling Curve is the data set examiners reach for: read both its seasonal sawtooth, which peaks in May and dips around September and October, and its long-term rise, and note that the guide does not require the details of the nitrogen cycle.
Simpson 倒数指数、保育路径与三周复习
生物多样性在考纲里分三层：生态系统多样性、物种多样性与遗传多样性。物种这一层看两个量，物种丰富度是物种数目，均匀度是各物种个体数分布得是否平均，丰富度相同而均匀度不同，多样性指数就不一样。技能清单要求会套用 Simpson 倒数指数处理样方数据，指数越高表示多样性越高。A4.2.5 要求用可核查的调查证据说明多样性危机，并把重复调查当作判断变化的必要条件，单次调查只能给一个基准。A4.2.6 把人为原因归成过度捕猎与开采、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。A4.2.7 强调保育没有单一方案，就地保护、保护区管理、退化生态系统的恢复、动物园与植物园的迁地保护、种子库与组织库都要用上。复习按三周走，第一周过 C4.1 的种群估计与种间关系，第二周画图并算两个指数，第三周用真题练 1B 数据题并整理错题。
Biodiversity is read at three levels, ecosystem, species and genetic, and the species level uses two measures: richness, the number of species, and evenness, how evenly individuals are distributed among them. The skills list expects you to apply the Simpson reciprocal index to quadrat data, where a higher value means greater diversity, and A4.2.5 requires evidence of a biodiversity crisis from repeated surveys, since a single survey gives only a baseline. Conservation needs several approaches at once, from in situ protection and reserve management through restoration of degraded ecosystems to ex situ measures such as zoos, botanic gardens and seed or tissue banks.
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