生物 · 第8单元生态学 · 阅读约 14 分钟 · 更新于 2026-05-10

AP生物学群落生态学 — AP 生物学

AP 生物学 · 第8单元生态学 · 14 min read

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

📐 Worked Example

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。

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。
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。
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。
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.

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.

📐 Worked Example

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.

Recall the key distinction between succession types: primary succession requires complete removal of soil, while secondary succession leaves intact soil after disturbance.
Justify the classification: The scenario explicitly states soil remains intact, so this is secondary succession.
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.
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

📐 Worked Example

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.

Uninvaded plot calculation: $N=120$, so:
$N(N-1) = 120 \times 119 = 14280$
Sum of $n(n-1)$ across all species:
$(25 \times 24) + (35 \times 34) + (20 \times 19) + (30 \times 29) + (10 \times 9) = 3130$
$D_{uninvaded} = 1 - \frac{3130}{14280} \approx 0.781$
Invaded plot calculation: $N=120$, same $N(N-1) = 14280$:
$\sum n(n-1) = (85 \times 84) + (10 \times 9) + (15 \times 14) + (5 \times 4) + (5 \times 4) = 7480$
$D_{invaded} = 1 - \frac{7480}{14280} \approx 0.476$
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.

Common Pitfalls

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

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

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

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

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

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

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AP生物学 群落生态学 — AP 生物学

1. 种间相互作用与竞争排除 ★★☆☆☆ ⏱ 3 min

2. 群落多样性：辛普森多样性指数 ★★★☆☆ ⏱ 4 min

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

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

Common Pitfalls

Quick Reference Cheatsheet

更多学习指南

AP生物学群落生态学 — AP 生物学