Chapter 3: Life Cycles and Biological Change Lesson 13 Causes of Extinction

Source TCAP Coach TCAP Coach 5 th grade 5 th grade Science Science

Objective The student will compare the causes that led to the extinction of various organisms. The student will compare the causes that led to the extinction of various organisms.

Cause of Extinction When the habitat that an organism is adapted to changes or disappears, fewer of these organisms survive. When the habitat that an organism is adapted to changes or disappears, fewer of these organisms survive. When fewer organisms survive, there are fewer left to reproduce. When fewer organisms survive, there are fewer left to reproduce. Over time, the population gets smaller and smaller. Over time, the population gets smaller and smaller. Eventually, the species will become extinct. Eventually, the species will become extinct.

Cause of Extinction In this lesson, you will learn about the causes of extinction. In this lesson, you will learn about the causes of extinction.

Habitat Destruction Plants and animals thrive in certain habitats. When their natural habitat shrinks, fewer members of a population can thrive. Plants and animals thrive in certain habitats. When their natural habitat shrinks, fewer members of a population can thrive. Humans have changed much of the surface of the Earth. Humans have changed much of the surface of the Earth.

Habitat Destruction We use land for our houses and for growing crops. Whenever an acre of land is changed from a natural habitat, such as a forest, to cleared land for human use, habitats become smaller. We use land for our houses and for growing crops. Whenever an acre of land is changed from a natural habitat, such as a forest, to cleared land for human use, habitats become smaller. The animals that were living in the original forest must find a new habitat to live in. The animals that were living in the original forest must find a new habitat to live in.

Habitat Destruction When much of an animal’s habitat is destroyed, it is harder for that species to survive.

Habitat Destruction Even when some original habitat is left, this habitat is often broken into smaller, isolated pieces. Human activity can also pollute a natural habitat. People often use fertilizers and insecticides on crops and recreational areas. These chemicals move into animals’ habitats and can affect their life cycles. Many amphibian species are endangered because of pollution of the environment. Even when some original habitat is left, this habitat is often broken into smaller, isolated pieces. Human activity can also pollute a natural habitat. People often use fertilizers and insecticides on crops and recreational areas. These chemicals move into animals’ habitats and can affect their life cycles. Many amphibian species are endangered because of pollution of the environment.

Habitat Destruction

Other species become endangered when new species move into their habitat. Many of these new alien species are introduced by humans. Other species become endangered when new species move into their habitat. Many of these new alien species are introduced by humans. The new species can compete for food and space and put stress on native populations. The new species can compete for food and space and put stress on native populations. These new species often have few or no natural predators. These new species often have few or no natural predators.

Over-hunting Over the last 200 years, many animals have become extinct because of over-hunting. One example is the passenger pigeon. Over the last 200 years, many animals have become extinct because of over-hunting. One example is the passenger pigeon.

Over-hunting As Europeans began to settle the United States, they hunted passenger pigeons to eat and for sport. It is believed that the original population of passenger pigeons was well over a billion. As Europeans began to settle the United States, they hunted passenger pigeons to eat and for sport. It is believed that the original population of passenger pigeons was well over a billion. But by 1914, the species was extinct. Other bird species became extinct after they were hunted for their beautiful plumes. But by 1914, the species was extinct. Other bird species became extinct after they were hunted for their beautiful plumes.

Over-hunting Other species have been hunted to near extinction. The American bison was close to extinction for many years but has begun to make a recovery. This is because widespread hunting of bison has stopped and some of their habitat has been restored. Other species have been hunted to near extinction. The American bison was close to extinction for many years but has begun to make a recovery. This is because widespread hunting of bison has stopped and some of their habitat has been restored.

Mass Extinctions Throughout Earth’s history, there have been a few periods of mass extinctions. Throughout Earth’s history, there have been a few periods of mass extinctions. A mass extinction occurs when many species go extinct at the same time. A mass extinction occurs when many species go extinct at the same time. Mass extinctions may be caused by climate change. As the climate changes all over Earth, habitats all over Earth are changed and destroyed. Mass extinctions may be caused by climate change. As the climate changes all over Earth, habitats all over Earth are changed and destroyed.

Mass Extinctions A mass extinction happened when the dinosaurs became extinct. Many scientist believe that this mass extinction was caused by a meteor striking Earth. When the meteor struck Earth, huge amounts of dust blew into the atmosphere. This dust blocked sunlight and caused a cooling all over the Earth’s surface. As plants began to die out, so did animals that depended on the plants for food. Eventually the dinosaurs died out. Now we only have fossil evidence of the dinosaurs. A mass extinction happened when the dinosaurs became extinct. Many scientist believe that this mass extinction was caused by a meteor striking Earth. When the meteor struck Earth, huge amounts of dust blew into the atmosphere. This dust blocked sunlight and caused a cooling all over the Earth’s surface. As plants began to die out, so did animals that depended on the plants for food. Eventually the dinosaurs died out. Now we only have fossil evidence of the dinosaurs.

Mass Extinctions

Adaptations Not all species become extinct when their habitats change. Not all species become extinct when their habitats change. Some species have characteristics that can help them survive in a changing and changed habitat. Some species have characteristics that can help them survive in a changing and changed habitat. Over time, these characteristics can help them thrive in a new environment. Over time, these characteristics can help them thrive in a new environment. Small mammals living alongside the dinosaurs thrived after the dinosaurs became extinct. Small mammals living alongside the dinosaurs thrived after the dinosaurs became extinct.

Extinct Animals

Which term describes what happens when many species go extinct at the same time? A. Over-hunting A. Over-hunting B. Mass extinction B. Mass extinction C. Climate change C. Climate change D. metamorphosis D. metamorphosis

Which term describes what happens when many species go extinct at the same time? B. Mass extinction B. Mass extinction

What do scientist think is the main cause of mass extinctions? A. Over-hunting A. Over-hunting B. Pollution B. Pollution C. Climate change C. Climate change D. Habitat fragmentation D. Habitat fragmentation

What do scientist think is the main cause of mass extinctions? C. Climate change C. Climate change

Which of these helps an organism thrive in changing habitats? A. Pollution A. Pollution B. Habitat destruction B. Habitat destruction C. Adaptation C. Adaptation D. Climate change D. Climate change

Which of these helps an organism thrive in changing habitats? C. Adaptation C. Adaptation