How do natural and human disturbances disrupt ecosystems?
Topic 8.7 Disruptions to Ecosystems: explain how natural and human-caused disruptions affect ecosystems and how ecosystems respond.
A focused answer to AP Biology Topic 8.7, covering natural and human disturbances, invasive species, habitat loss, climate change, ecological succession, and how ecosystems respond and recover, with a worked example.
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What this topic is asking
The College Board (Topic 8.7) wants you to explain how natural and human-caused disruptions affect ecosystems, including invasive species, habitat loss and climate change, and how ecosystems respond and recover through processes such as succession.
Natural and human disruptions
Invasive species
Recovery through succession
Secondary succession is usually faster than primary succession because soil, seeds and nutrients are already present. The capacity to recover ties back to biodiversity: a more diverse ecosystem has more species available to recolonise and more functional redundancy, so it tends to recover more fully from disturbance.
Try this
Q1. State why invasive species often spread rapidly in a new ecosystem. [1 point]
- Cue. They usually lack the natural predators, parasites and competitors that limited them in their native range, so their populations can grow unchecked.
Q2. Explain how an ecosystem can recover after a fire. [2 points]
- Cue. Through secondary succession: pioneer species colonize the disturbed area and change conditions, and a series of communities replace one another until a stable community re-establishes.
Exam-style practice questions
Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AP 2020 (style)4 marksSection II (long FRQ excerpt). An invasive species with no natural predators is introduced to a lake. (a) Predict and explain the likely effects on the native community. (b) Explain how a disruption such as a fire can lead to ecological succession and eventual recovery.Show worked answer →
A 4-point predict-and-explain FRQ on ecosystem disruption.
(a) Predict and explain (2 points): (1 point) with no natural predators, the invasive species can grow rapidly and outcompete or prey on native species; (1 point) native populations decline, food webs are disrupted, and biodiversity falls.
(b) Explain (2 points): (1 point) a fire clears an area, after which pioneer species colonize and gradually change the conditions (secondary succession); (1 point) over time a series of communities replace one another until a stable community re-establishes, so the ecosystem can recover, helped by its biodiversity.
Markers reward predicting the invasive species' disruptive effect and explaining succession as the mechanism of recovery.
AP 2017 (style)1 marksSection I (multiple choice). An invasive species often causes harm in a new ecosystem because it: (A) always reproduces slowly. (B) lacks natural predators or competitors there. (C) immediately goes extinct. (D) increases the biodiversity of natives.Show worked answer →
The correct answer is (B).
An invasive species often lacks the natural predators, parasites or competitors that limited it in its native range, so its population can grow rapidly and outcompete or prey on native species, reducing biodiversity.
Related dot points
- Topic 8.6 Biodiversity: explain how biodiversity contributes to ecosystem stability and resilience.
A focused answer to AP Biology Topic 8.6, covering species and genetic diversity, how diversity supports ecosystem stability and resilience, the effects of low diversity, and a worked example using a diversity comparison.
- Topic 8.5 Community Ecology: explain the types of interactions between species in a community and their effects on the species involved.
A focused answer to AP Biology Topic 8.5, covering competition, predation, the niche, symbiosis (mutualism, commensalism, parasitism), keystone species and trophic relationships, with a worked interaction example.
- Topic 8.3 Population Ecology: explain exponential and logistic growth, carrying capacity, and the factors that regulate population size.
A focused answer to AP Biology Topic 8.3, covering exponential and logistic growth, carrying capacity, growth rate calculations, and the factors that shape population size, with a worked growth-rate calculation.
- Topic 7.11 Extinction: explain the causes of extinction, including mass extinctions, and its role in shaping biodiversity.
A focused answer to AP Biology Topic 7.11, covering the causes of extinction, background versus mass extinction, the five mass extinctions, adaptive radiation after extinction, and the current human-driven loss, with a worked example.
- Topic 8.2 Energy Flow Through Ecosystems: explain how energy flows through trophic levels and why energy is lost between levels.
A focused answer to AP Biology Topic 8.2, covering trophic levels, food chains and webs, the 10 percent rule, energy pyramids, productivity, and why energy decreases up the chain, with a worked energy-transfer calculation.
Sources & how we know this
- AP Biology Course and Exam Description — College Board (2020)