What's happening to this land?
This picture, taken in southern Mexico, shows land being cleared for agriculture. The forest has been cut down and burned to make room for a farm. In the process, homes of many plants and animals were destroyed. This is an example of habitat destruction.
From a human point of view, a habitat is where you live, go to school, and go to have fun. Your habitat can be altered, and you can easily adapt. Most people live in a few different places and go to a number of different schools throughout their life. But a plant or animal may not be able to adapt to a changed habitat. A habitat is the natural home or environment of an organism. Humans often destroy the habitats of other organisms. Habitat destruction can cause the extinction of species. Extinction is the complete disappearance of a species. Once a species is extinct, it can never recover. Some ways humans cause habitat destruction are by clearing land and by introducing non-native species of plants and animals.
Clearing land for agriculture and development is a major cause of habitat destruction. Within the past 100 years, the amount of total land used for agriculture has almost doubled. Land used for grazing cattle has more than doubled. Agriculture alone has cost the United States half of its wetlands (Figure below) and almost all of its tallgrass prairies. Native prairie ecosystems, with their thick fertile soils, deep-rooted grasses, diversity of colorful flowers, burrowing prairie dogs, and herds of bison and other animals, have virtually disappeared (Figure below).
Other habitats that are being rapidly destroyed are forests, especially tropical rainforests. The largest cause of deforestation today is slash-and-burn agriculture (shown in the opening image). This means that when people want to turn a forest into a farm, they cut down all of the trees and then burn the remainder of the forest. This technique is used by over 200 million people in tropical forests throughout the world.
As a consequence of slash-and-burn agriculture, nutrients are quickly lost from the soil. This often results in people abandoning the land within a few years. Then the top soil erodes and desertification can follow. Desertification turns forest into a desert, where it is difficult for plants to grow. Half of the Earth’s mature tropical forests are gone. At current rates of deforestation, all tropical forests will be gone by the year 2090.
One of the main causes of extinction is introduction of exotic species into an environment. These exotic and new species can also be called invasive species or non-native species. These non-native species, being new to an area, may not have natural predators in the new habitat, which allows their populations to easily adapt and grow. Invasive species out-compete the native species for resources. Sometimes invasive species are so successful at living in a certain habitat that the native species go extinct (Figure below).
Recently, cargo ships have transported zebra mussels, spiny waterfleas, and ruffe (a freshwater fish) into the Great Lakes (Figure below). These invasive species are better at hunting for food. They have caused some of the native species to go extinct.
Invasive species can disrupt food chains, carry disease, prey on native species directly, and out-compete native species for limited resources, like food. All of these effects can lead to extinction of the native species.
Other causes of habitat destruction include poor fire management, overfishing, mining (Figure below), pollution, and storm damage. All of these can cause irreversible changes to a habitat and ecosystem.
Examples of Habitat Destruction
A habitat that is quickly being destroyed is the wetland. By the 1980s, over 80% of all wetlands in parts of the U.S. were destroyed. In Europe, many wetland species have gone extinct. For example, many bogs in Scotland have been lost because of human development.
Another example of species loss due to habitat destruction happened on Madagascar’s central highland plateau. From 1970 to 2000, slash-and-burn agriculture destroyed about 10% of the country’s total native plants. The area turned into a wasteland. Soil from erosion entered the waterways. Much of the river ecosystems of several large rivers were also destroyed. Several fish species are almost extinct. Also, some coral reef formations in the Indian Ocean are completely lost.
- There are many causes of habitat destruction, including clearing of land and introduction of invasive species.
- Slash-and-burn agriculture can lead to desertification, meaning the fertile top soil is lost.
Use the resource below to answer the questions that follow.
Explore More I
- Suburban Growth Stresses Streams at http://www.youtube.com/watch?v=54k5vaWIRdA
Explore More II
- The Ecology of Climate Change at http://www.youtube.com/watch?v=isPGjChdby8 (8:07)
- What types of trees dominate boreal forests?
- How is climate change affecting the amount of fires occurring in Alaska? How is this affecting the ecosystem?
- How do conifer forests differ from deciduous forest in their effect on carbon? How may this feed into climate change?
- How may the thawing of permafrost affect the Global Carbon Cycle? How is the carbon in the permafrost similar to the carbon in fossil fuel?
- What is a habitat?
- What are the primary ways that humans destroy habitats?
- Why may invasive species thrive in a new area? Why is this an issue?
- Describe slash-and-burn agriculture.