Extinction & rapid change
Explain how rapid environmental change can increase extinction risk when populations cannot survive, reproduce, adapt or reach suitable habitat, using historical and present-day examples.
What a learner can do afterwards
- Explains how rapid change can leave too little time or useful inherited variation for populations to survive, increasing extinction risk.
- Gives a historical example (e.g. woolly mammoth, dodo) and a contemporary example of threatened extinction
- Distinguishes background extinction from mass extinction by considering worldwide species loss and the geological timescale.
- Explains how human activity (habitat loss, hunting, climate change) is driving current species loss
1 · Read
Natural selection can make helpful inherited traits more common between generations. The time needed varies, and individuals do not choose new inherited traits. Rapid change can leave too little time or useful variation for populations to survive and reproduce. Reaching suitable habitat can also help survival. Extinction means every individual of a species has died. It can follow rapid change, a long decline or a disaster.
Woolly mammoths lived in cold grassland habitats. Warming as the last ice age ended changed those habitats. Hunting may also have added pressure. Mammoth populations disappeared at different times, and some survived for thousands of years after the ice age. Scientists study how habitat change, hunting and other pressures contributed. African and Asian elephants still exist today.
The vaquita is a porpoise found only in the northern Gulf of California. It is critically endangered. Vaquitas can become trapped and drown in gillnets set for other species. Human activities threaten other species too. Clearing forests removes food and shelter. Harmful hunting kills individuals, and human-caused climate change alters conditions that species depend on. These pressures can reduce survival or reproduction.
Background extinction is the usual loss of species outside mass extinctions; its rate varies. A mass extinction removes a large share of species worldwide in a short time on Earth's geological scale. Asteroid impacts or huge volcanic eruptions can cause one. Current extinction rates exceed estimated background levels. A high rate warns of danger, but rate alone does not show how large a share of all species has disappeared.
Conservation aims to reduce threats while individuals can still survive and reproduce. Protecting and restoring habitat helps species that have lost food or shelter. Reducing harmful hunting gives populations a chance to recover. For vaquitas, keeping gillnets out of their habitat tackles the direct danger of drowning. These actions can help, but recovery is not guaranteed.
Extinction means no individuals of a species remain. Rapid change can raise the risk. Protecting habitats and reducing harmful hunting or fishing can help species survive.
Lesson, questions and flashcards written for this dataset.
Three readings written for this dataset. The California Academy of Sciences created "Biodiversity and extinction, then and now" and "How does climate change affect biodiversity?", included in Khan Academy courses. The adaptation video is also linked from a Khan Academy course.
More to read
Why change has different outcomes
A changed habitat does not affect every species alike. Some populations contain inherited differences that help individuals survive and leave offspring. Useful traits can then become more common. Other populations may lack suitable variation or decline before those traits can spread.
Moving to suitable habitat can sometimes help too. Neither movement nor adaptation is always possible. A threat may also kill individuals directly, as dangerous fishing nets do. Extinction describes the final outcome when no individuals of a species remain, rather than one particular cause of decline.
Choose help that matches the threat
Ask what is preventing individuals from surviving or producing young. Habitat protection can preserve food and shelter. Restoring damaged habitat may return resources that have been lost. Reducing harmful hunting addresses direct deaths instead.
For vaquitas, gillnets are a direct danger because trapped porpoises can drown. Keeping those nets out of vaquita habitat tackles that danger. A plan can involve several actions when threats overlap. Protection improves opportunities for survival and reproduction, but a small population may still face risks, so recovery cannot be promised.
A decline in one place or everywhere?
Food, water and shelter help a habitat support living things. Losing these resources can reduce survival or reproduction. Population size can fall, but it does not always settle at one fixed number.
A species disappearing from one lake or forest is a local extinction if it survives elsewhere. Global extinction means none remain anywhere. To tell the difference, scientists need information about the species' full range. A species found in only one small area may lose its entire habitat when that area changes.
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