AP生物学群落生态学

AP 生物学· AP Biology CED — 生态学· 14 分钟阅读

1. 种间相互作用与竞争排除★★☆☆☆⏱ 3 min

种间相互作用根据其对每个相互作用个体适合度的净效应分类。AP考试考察四种核心相互作用类型：

竞争 (-/-): 两个物种都因共享有限资源而适合度降低
捕食/寄生 (+/-): 一个物种适合度提升，以另一物种适合度下降为代价
互利共生 (+/+): 两个物种都从相互作用中获得更高适合度
偏利共生 (+/0): 一个物种适合度提升，另一物种完全不受影响

📘 定义

竞争排除原理

两个物种无法在同一环境中长期占据完全相同的基础生态位。效率更高的竞争者会将较弱的竞争者在局域范围内排除。

例:

该原理最早由高斯用两种草履虫（Paramecium）的实验证明。

📘 定义

生态位类型

基础生态位 vs 现实生态位

生态位是物种生存和繁殖所需的全部生物和非生物资源的集合。基础生态位是不存在竞争时物种可以利用的全部资源范围；现实生态位是存在竞争时物种实际利用的较小范围。

📐 例题

一名研究者研究了生长在同一草原生境中的两种野生向日葵。单独生长时，物种A可在pH 5.5至7.0的土壤中生长；但当物种B存在时，物种A仅能在pH 5.5至6.2的土壤中生长。请指出物种A的现实生态位，并解释该结果支持竞争排除还是资源分配。

1
记住：现实生态位是存在竞争时生物实际利用的资源范围，而基础生态位是不存在竞争时的范围。
2
对应给定数据：单独生长时，物种A的基础生态位是pH 5.5–7.0。存在竞争时，它被限制在pH 5.5–6.2，因此这个范围就是它的现实生态位。
3
结果分析：两个物种都共存，每个都被限制在基础生态位的一部分。竞争排除会导致一个物种被完全消除，这里并没有发生这种情况。
4
结论：物种A的现实生态位是pH 5.5–6.2，该观察结果支持资源分配。

Exam tip:

在要求区分基础生态位和现实生态位的FRQ中，一定要明确提及竞争的作用才能拿到满分。

2. 群落多样性：辛普森多样性指数★★★☆☆⏱ 4 min

群落多样性有两个核心组成部分：物种丰富度（群落中不同物种的总数量）和相对丰度（每个物种占群落总个体数的比例）。辛普森多样性指数同时考虑了丰富度和均匀度（相对丰度的均衡程度），因此比仅用丰富度更全面地衡量多样性。

D = 1 - \left( \frac{\sum n(n-1)}{N(N-1)} \right)

Where $n$ = number of individuals of a single species, $N$ = total number of individuals across all species, and $D$ ranges from 0 to 1. Values closer to 1 indicate higher diversity, while values closer to 0 indicate lower diversity.

📐 例题

研究者对一片正在恢复的森林中一块10m x 10m样地进行采样，共计数到50棵树木，各物种计数如下：物种1 = 20，物种2 = 18，物种3 = 12。请计算该样地的辛普森多样性指数。

1
Confirm total number of individuals: $N = 20 + 18 + 12 = 50$ , which matches the given total.
2
$N(N-1) = 50 \times 49 = 2450$
3
Calculate $n (n - 1)$ for each species:
4
$\text{Species 1}: 20 \times 19 = 380 \\ \text{Species 2}: 18 \times 17 = 306 \\ \text{Species 3}: 12 \times 11 = 132$
5
Sum the $n (n - 1)$ values: $380 + 306 + 132 = 818$
6
Plug into the formula:
7
$D = 1 - \left(\frac{818}{2450}\right) = 1 - 0.334 = 0.666$

Exam tip:

Always double-check that you subtract the fraction from 1. AP question writers frequently use the unsubtracted dominance value as a distractor for MCQs.

3. Ecological Succession & Keystone Species★★☆☆☆⏱ 3 min

Ecological succession is the predictable, sequential change in community structure over time following a disturbance that alters the existing community. It is divided into two main types based on starting conditions after disturbance:

Primary succession: Occurs when all soil and nearly all living organisms are removed, for example after a volcanic eruption creates new rock or a glacier retreats leaving bare bedrock. Pioneer species (lichens, mosses) break down rock to build soil over centuries, eventually leading to a stable climax community.
Secondary succession: Occurs when a disturbance removes most above-ground vegetation but leaves the soil profile intact, for example after a wildfire or clear-cutting. Secondary succession proceeds much faster than primary succession because soil and native seeds are already present.

📘 定义

Keystone Species

A species that has a disproportionately large effect on community structure relative to its biomass or abundance. Removing a keystone species causes dramatic collapse of community diversity, often via a trophic cascade, where indirect effects ripple through all lower trophic levels.

📐 例题

A wildfire burns through a Rocky Mountain conifer forest, removing 90% of above-ground vegetation but leaving the majority of the soil profile intact. Researchers measure tree community diversity 10, 50, and 100 years after the fire, leading up to the climax community. Is this primary or secondary succession? Justify your answer and describe the trend in Simpson’s Diversity Index over this period.

1
Recall the key distinction between succession types: primary succession requires complete removal of soil, while secondary succession leaves intact soil after disturbance.
2
Justify the classification: The scenario explicitly states soil remains intact, so this is secondary succession.
3
Describe the diversity trend: 10 years after the fire, only a few fast-growing pioneer species are abundant, so diversity is low. As time passes, slower-growing climax species colonize and coexist with remaining pioneer species, increasing diversity.
4
Conclusion: This is secondary succession, and Simpson’s D will increase from 10 to 100 years after the fire before stabilizing at a high level in the climax community.

Exam tip:

Always explicitly mention the presence or absence of intact soil in your FRQ justification for succession type—this is almost always a required scoring point.

4. AP Style Practice Check★★★★☆⏱ 4 min

✓ 快速检测

Test your understanding with this AP-style multiple choice question:

A marine ecologist compares two intertidal communities. Community 1 has 4 species with the following counts: 25, 25, 25, 25. Community 2 has 5 species with the following counts: 91, 2, 2, 2, 3. Which of the following correctly compares the species richness and Simpson's Diversity Index of the two communities?
- A) Community 2 has higher species richness and higher Simpson's D than Community 1
- B) Community 2 has higher species richness, but Community 1 has higher Simpson's D than Community 2
- C) Community 1 has higher species richness and higher Simpson's D than Community 1
- D) Species richness is the same for both communities, but Community 1 has higher Simpson's D
显示答案
B —
Correct. Species richness is simply the number of species: Community 2 has 5 species, so higher richness than Community 1's 4. Simpson's D accounts for evenness: Community 1 is perfectly even, so its D (~0.758) is much higher than Community 2's D (~0.171), where one species dominates.

📐 例题

Ecologists study the effect of invasive garlic mustard on understory plant communities in Midwestern deciduous forests. They sample two 100m² plots: one uninvaded, and one invaded by garlic mustard, with both plots having 120 total individuals. Counts: Uninvaded: Trillium (25), Trout lily (35), Wild geranium (20), Spring beauty (30), Garlic mustard (10). Invaded: Garlic mustard (85), Trillium (10), Trout lily (15), Wild geranium (5), Spring beauty (5). Calculate Simpson's Diversity Index for both plots, and interpret your result in the context of invasive species impact.

1
Uninvaded plot calculation: $N = 120$ , so:
2
$N(N-1) = 120 \times 119 = 14280$
3
Sum of $n (n - 1)$ across all species:
4
$(25 \times 24) + (35 \times 34) + (20 \times 19) + (30 \times 29) + (10 \times 9) = 3130$
5
$D_{uninvaded} = 1 - \frac{3130}{14280} \approx 0.781$
6
Invaded plot calculation: $N = 120$ , same $N (N - 1) = 14280$ :
7
$\sum n(n-1) = (85 \times 84) + (10 \times 9) + (15 \times 14) + (5 \times 4) + (5 \times 4) = 7480$
8
$D_{invaded} = 1 - \frac{7480}{14280} \approx 0.476$
9
Interpretation: Invasion by garlic mustard reduces overall understory plant diversity. The uninvaded community has a much higher Simpson's D than the invaded community. Garlic mustard outcompetes native species, reducing native richness and evenness to lower overall community diversity.

5. 常见陷阱

错误做法:

Calling interspecific competition a +/- interaction.

原因:

Students confuse competition with predation, or assume only the losing species is harmed.

正确做法:

Always classify competition as -/- because both species have reduced access to resources and lower fitness than they would without competition.

错误做法:

Reporting Simpson's Diversity Index as $\frac{\sum n ( n - 1 )}{N ( N - 1 )}$ instead of 1 minus that value.

原因:

Some textbooks use this alternative value to measure species dominance, not diversity.

正确做法:

Remember AP uses the diversity version where higher values equal higher diversity, so always subtract the ratio from 1 before reporting.

错误做法:

Assuming higher species richness always means higher Simpson's diversity.

原因:

Students forget Simpson's D accounts for relative abundance as well as richness.

正确做法:

When comparing diversity, always check evenness: a community with 10 species dominated by one species has lower D than a community with 5 evenly distributed species.

错误做法:

Claiming primary succession happens 'first' before secondary succession.

原因:

Students misinterpret the prefixes 'primary' and 'secondary' as order of events, not starting conditions.

正确做法:

Always distinguish the two based on whether intact soil remains after disturbance (secondary) or is completely removed (primary).

错误做法:

Labeling the most abundant species in a community as a keystone species.

原因:

Students confuse keystone species with dominant species, which are abundant and have large effects.

正确做法:

Remember keystone species are defined by their disproportionate effect relative to their abundance; rare top predators are keystone, abundant trees are dominant.

错误做法:

Stating that climax communities are permanent and unchanging.

原因:

Older textbooks describe climax communities as stable, but AP CED emphasizes that disturbance is a natural part of all ecosystems.

正确做法:

Describe climax communities as relatively stable over long periods, but still subject to future disturbances that restart succession.

6. 速查表

Category	Formula / Rule	Notes
Interspecific Interaction Classification	Competition = (-/-); Predation/Parasitism = (+/-); Mutualism = (+/+); Commensalism = (+/0)	Classified by net fitness impact on each species
Competitive Exclusion Principle	No two species with identical niches coexist permanently	One species outcompetes the other for local extinction
Niche Definitions	Fundamental = no competition; Realized = with competition	AP tests this distinction more than other concepts here
Simpson's Diversity Index	D = 1 - \left( \frac{\sum n(n-1)}{N(N-1)} \right)	Higher $D$ = higher diversity; $n$ = per species count, $N$ = total individuals
Succession Types	Primary = no intact soil; Secondary = intact soil remains	Distinguished by starting conditions, not order of events
Keystone Species	Disproportionate effect relative to abundance/biomass	Removal causes major diversity loss via trophic cascades

真题中的出现

AI 根据考纲规律估算的考点位置,请对照官方真题核实准确性。仅作复习重点参考。

2023 · MCQ
比较群落多样性值
2022 · FRQ
分析关键种的作用
2021 · MCQ
对种间相互作用进行分类

下一步

Mastering community ecology provides the foundation for understanding broader ecosystem dynamics and global change impacts on biodiversity, which are common high-weight topics in AP Biology FRQ sections. The concepts you learned here, particularly diversity measurement and species interactions, connect directly to topics like conservation biology, invasive species management, and the impact of climate change on ecological communities. You will also reuse the niche concept when exploring evolutionary adaptations and species distribution patterns in other units. Building on this knowledge will help you connect individual concepts to the big picture of ecology that is frequently tested on the AP exam.