What pushes a species toward extinction, and how do we pull it back?
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.
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What this topic is asking
The College Board (Topic 9.9) wants you to explain the factors that make species vulnerable to extinction and describe how endangered species are protected.
What makes a species vulnerable
Human threats
Conservation strategies
Why this matters
Endangered species and human impacts on biodiversity (Topic 9.10) are the conservation climax of the course, drawing on biodiversity (Unit 2), island biogeography (small ranges) and specialist species (Unit 3). The vulnerability traits and the keystone-species idea are recurring AP exam points, and conservation laws are standard examples.
Try this
Q1. Identify two traits that make a species more vulnerable to extinction. [1 point]
- Cue. Any two of small or shrinking range, low reproductive rate, specialist niche, large body size, small population.
Q2. Explain why protecting a keystone species can protect a whole ecosystem. [2 points]
- Cue. A keystone species has a large effect on its ecosystem relative to its abundance, so many other species depend on it; protecting it preserves the ecosystem's structure and the species that rely on it.
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 2021 (style)4 marksSection II (FRQ). (a) Identify two traits that make a species more vulnerable to extinction. (b) Identify two human activities that endanger species. (c) Describe one conservation strategy used to protect endangered species. (d) Explain why protecting a keystone species can protect a whole ecosystem.Show worked answer →
A 4-point FRQ on endangered species.
(a) Identify (1 point): any two of small or shrinking range, low reproductive rate, specialist niche, large body size, or small population.
(b) Identify (1 point): any two of habitat destruction, overharvesting, pollution, introduction of invasive species, or climate change.
(c) Describe (1 point): protected areas and habitat preservation, captive breeding and reintroduction, or laws such as the Endangered Species Act and CITES (regulating trade).
(d) Explain (1 point): a keystone species has a large effect on its ecosystem relative to its abundance, so protecting it preserves the structure and many other species that depend on it.
Markers reward two valid vulnerability traits, two valid human threats, a valid conservation strategy, and the keystone-species explanation.
AP 2018 (style)1 marksSection I (multiple choice). Which trait makes a species most vulnerable to extinction? (A) A wide geographic range and high reproductive rate (B) A small, specialized range and low reproductive rate (C) A generalist diet and rapid breeding (D) A large, growing population. Justify your choice.Show worked answer →
A 1-point MCQ on extinction risk. The answer is (B).
Species with a small, specialized range and low reproductive rate are most vulnerable: they cannot easily recover from losses or move when conditions change, and a single disturbance can wipe out much of the population. A wide range with high reproduction (A), a generalist with rapid breeding (C), and a large growing population (D) are all more resilient. The trap is choosing resilient traits; vulnerability comes from being specialized, slow-breeding and limited in range.
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 9.8 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.
- 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.
- Topic 2.3 Island Biogeography: explain how island size and distance from the mainland determine species richness, and apply the theory to habitat fragments.
A focused answer to APES Topic 2.3, covering the theory of island biogeography, the effects of island size and distance, immigration and extinction rates, endemism, and its application to habitat fragmentation, with a worked island-comparison question.
Sources & how we know this
- AP Environmental Science Course and Exam Description — College Board (2020)