Extinction is the disappearance of every individual of a species from the entire planet. Did you know that scientists estimate that more than 99% of the species that have ever existed on this planet are extinct? They are gone, never to return! Did you also know that scientists think that the rate at which species are becoming extinct is increasing? This affects diversity on our planet, and part of the problem lies with human beings. In this lesson, you will learn about the human impact on diversity.

As you just read, extinction of a particular animal or plant species occurs when there are no more individuals of that species alive anywhere in the world — the species has died out.

A species can become extinct in two ways:

1. by natural means
2. by human interaction with that species

In nature, a species can become extinct because of terrible events such as volcanic eruptions, meteors hitting the earth, floods, or fires. Extinctions can also be caused by disease or lack of food because of over-population.

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Today, however, humans are causing most of the extinctions that occur.

There are three main human related causes:

1. habitat destruction
2. introduction of non-native species
3. over-hunting

Habitat Destruction

Habitat destruction is very simple. You see it all around you. When a new neighbourhood is built, habitat for animals is destroyed. When someone clears forest to make another hay or grain field, habitat is destroyed.

Consider the statement below about how fast rainforests are being destroyed. Keep in mind that rainforests have the highest diversity of species found anywhere on the planet!

Another way that people destroy habitat is through pollution. It can affect areas farther away as well as the immediate area. An example of this is the spreading of fertilizer or pesticides near a stream. They can get into the stream and unintentionally kill species within the stream. As this stream passes by more farms, it may pick up more fertilizer or pesticides until the stream itself is toxic to both plants and animals.

 

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Introduction of Non-Native Species

Introduction of non-native species also has negative effects on habitat. Did you know that horses and cattle are not native to North America? They were brought from Europe. Think of all the habitat that has been changed so that cows and horses have pasture and food for the winter.

One extreme example of the introduction of non-native species having a negative effect on a habitat occurred in Australia. The cane toad was brought in to kill agricultural pests, but it is now a pest itself. Read more about the cane toad below.

The cane toad has poison glands, and the tadpoles are highly toxic to most animals if ingested. Because of its voracious appetite, the cane toad has been introduced to many regions of the Pacific and the Caribbean islands as a method of agricultural pest control, notably in the case of Australia in 1935, and derives its common name from its use against sugar cane pests. The cane toad is now considered a pest in many of its introduced regions, because its toxic skin kills many native predators when ingested. It has many negative effects on farmers because of pets and animals eating the creatures.

 

 

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The cane toad population continues to grow, and now people are trying to figure how to deal with the cane toads. What started as a good idea is now very troubling indeed.

From: http://en.wikipedia.org/wiki/Cane_toad

Over-hunting is another way that humans affect diversity. When the first European hunters and settlers arrived on the prairies, there were huge herds of bison. But they were shot by the thousands for their hides. Now you can only see these plains bison in places like Elk Island National Park. The only way they survive today is in places set aside for them.

 

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