Why can a species that is harmless at home wreck an ecosystem somewhere new?
Topic 9.8 Invasive Species: explain what makes a species invasive and describe the impacts of invasive species and how they are managed.
A focused answer to APES Topic 9.8, covering what makes a species invasive, how they are introduced, why the lack of natural predators lets them spread, their impacts on native species and ecosystems, the link to climate change, and methods of control, with a worked exponential-spread reasoning example.
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What this topic is asking
The College Board (Topic 9.8) wants you to explain what makes a species invasive and describe the impacts of invasive species and how they are managed.
What makes a species invasive
Why they spread so fast
Impacts, climate links and control
Why this matters
Invasive species are a leading cause of biodiversity loss (the "I" in the HIPPCO threats of Topic 9.10) and connect Unit 9 to populations (Unit 3, generalists and unchecked growth) and biodiversity (Unit 2). The climate link makes them a global-change topic, and the lack-of-natural-controls explanation is a standard AP exam point.
Try this
Q1. Define an invasive species. [1 point]
- Cue. A non-native species introduced to an ecosystem where it causes ecological or economic harm.
Q2. Explain why invasive species often spread rapidly in a new ecosystem. [2 points]
- Cue. The new ecosystem usually lacks the predators, parasites and competitors that kept the species in check in its native range, so its population grows unchecked and outcompetes native species.
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 2022 (style)4 marksSection II (FRQ). (a) Define an invasive species. (b) Explain why invasive species often spread rapidly in a new ecosystem. (c) Identify two impacts of invasive species on native ecosystems. (d) Describe one method used to control invasive species.Show worked answer →
A 4-point FRQ on invasive species.
(a) Define (1 point): a non-native species introduced to an ecosystem where it causes ecological or economic harm.
(b) Explain (1 point): in the new ecosystem they often have no natural predators, parasites or competitors to keep them in check, so their population grows rapidly.
(c) Identify (1 point): any two of outcompeting or preying on native species, reducing biodiversity, spreading disease, or altering habitat.
(d) Describe (1 point): physical removal, chemical control (pesticides), or biological control (introducing a natural predator or pathogen), plus prevention through inspection and quarantine.
Markers reward the non-native-and-harmful definition, the lack-of-natural-controls explanation, two valid impacts, and a valid control method.
AP 2018 (style)1 marksSection I (multiple choice). Invasive species often outcompete native species mainly because they: (A) are always larger than native species (B) lack natural predators and competitors in the new ecosystem (C) require less sunlight (D) cannot reproduce quickly. Justify your choice.Show worked answer →
A 1-point MCQ on invasive species. The answer is (B).
Invasive species spread because the new ecosystem usually lacks the predators, parasites and competitors that controlled them in their native range, so their populations grow unchecked and outcompete natives. They are not always larger (A), do not necessarily need less light (C), and they typically reproduce quickly, not slowly (D). The trap is looking for a trait of the invader itself; the key factor is the absence of natural controls in the new ecosystem.
Related dot points
- Topic 9.10 Human Impacts on Biodiversity: identify the major human causes of biodiversity loss (HIPPCO) and explain why declining biodiversity matters.
A focused answer to APES Topic 9.10, covering the HIPPCO causes of biodiversity loss, why habitat loss is the largest, the importance of biodiversity for ecosystem services and resilience, the sixth mass extinction, and conservation responses, with a worked species-loss reasoning example.
- Topic 9.9 Endangered Species: explain the factors that make species vulnerable to extinction and describe how endangered species are protected.
A focused answer to APES Topic 9.9, covering what makes a species endangered, the traits that increase extinction risk, the human causes, conservation strategies (protected areas, captive breeding, the Endangered Species Act, CITES), and keystone species, with a worked minimum-viable-population example.
- Topic 9.5 Global Climate Change: describe the evidence and effects of global climate change and explain the role of positive feedback loops.
A focused answer to APES Topic 9.5, covering the evidence for global climate change, its effects (rising temperatures, melting ice, sea-level rise, extreme weather, shifting species), positive feedback loops (ice-albedo, permafrost methane, water vapor), the difference between weather and climate, and mitigation and adaptation, with a worked sea-level reasoning example.
- Topic 2.1 Introduction to Biodiversity: describe the three levels of biodiversity and explain how genetic and species diversity contribute to ecosystem resilience.
A focused answer to APES Topic 2.1, covering genetic, species and habitat diversity, species richness and evenness, the value of genetic diversity, bottlenecks and resilience, with a worked diversity-comparison question.
- Topic 3.1 Generalist and Specialist Species: distinguish generalist from specialist species and explain how a changing or stable environment favors each.
A focused answer to APES Topic 3.1, covering the difference between generalist and specialist species, the role of niche breadth, and how stable versus changing environments favor each strategy, with a worked species-comparison question.
Sources & how we know this
- AP Environmental Science Course and Exam Description — College Board (2020)