Extinction
Extinction is the permanent loss of a species. Understanding population decline, extinction risk, biodiversity, and conservation helps explain why the disappearance of one species can have effects far beyond that population.
Extinction
What Is Extinction?
Extinction occurs when a species no longer has any living individuals anywhere on Earth. Once a species is extinct, its population cannot naturally recover because there are no surviving members of that species.
Extinction is different from a local population disappearing. A species may disappear from one region while still surviving elsewhere. That is called local extinction, or extirpation. The species itself is not globally extinct if populations remain somewhere else.
Global extinction = zero surviving individuals anywhere. A species can disappear from one location without becoming globally extinct.
What Causes Extinction?
Extinction can result from natural environmental change, but human activities have greatly increased extinction pressure for many species. Major causes include habitat loss, overexploitation, invasive species, pollution, disease, and climate change.
Loss and fragmentation
When suitable habitat disappears or becomes isolated, populations may become too small to survive.
Overexploitation
Hunting, fishing, harvesting, or collecting organisms faster than populations can replace them can drive severe declines.
Invasive species & disease
New competitors, predators, parasites, or pathogens can place strong pressure on native populations.
Climate & pollution
Rapid environmental changes can make conditions unsuitable or disrupt reproduction and survival.
Why Are Small Populations More Vulnerable?
As a population becomes smaller, random events can have a larger effect on its survival. A storm, disease outbreak, change in food availability, or unusual reproductive year may strongly affect a small population.
Small populations may also experience reduced genetic diversity. With fewer individuals, there may be fewer alleles available for natural selection to act on, potentially reducing the population's ability to respond to environmental change.
Small populations can also face problems finding mates. These effects can reinforce one another, making recovery increasingly difficult as population size declines.
How Does Extinction Affect Biodiversity?
When a species becomes extinct, species richness decreases because one species has been removed from the community or from Earth entirely. The ecological consequences can extend beyond the extinct species if it had important interactions with other organisms.
A species may serve as a predator, prey, pollinator, seed disperser, decomposer, competitor, or habitat modifier. Losing it can therefore alter food webs, nutrient cycling, population sizes, and ecosystem processes.
Extinction is not only a loss of one population. Because organisms interact, the disappearance of one species can change other populations and ecological processes.
Can Extinction Be Prevented?
Conservation biology aims to reduce extinction risk by protecting populations and the ecosystems they depend on. Strategies can include habitat protection and restoration, wildlife corridors, sustainable resource use, captive breeding or managed propagation in some cases, control of invasive species, and legal protections.
Preventing extinction is generally easier than restoring a species after its population has reached extremely low numbers. Conservation therefore often focuses on identifying populations at risk early and addressing the causes of decline.
Common Misconceptions
If You See This on a Test, Think This
Quick Practice
1. What is extinction?
2. What is the difference between global and local extinction?
3. Why are very small populations vulnerable to extinction?
4. How can extinction affect a food web?
5. Name one way conservation can reduce extinction risk.
Key Takeaways
- Global extinction occurs when no living individuals of a species remain anywhere on Earth.
- Local extinction occurs when a species disappears from a particular area but survives elsewhere.
- Habitat loss, overexploitation, invasive species, pollution, disease, and climate change can increase extinction risk.
- Small populations are often more vulnerable because demographic, genetic, and environmental effects become more important.
- Extinction reduces biodiversity and can alter ecological interactions.
- Conservation focuses on reducing extinction risk before populations become unrecoverably small.
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