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Part XVII : Human Influences on Populations Index

Some Human Activities which Modify Habitats
Introduced Species
How Humans Can Help
Biodiversity
Natural Parks in France

Topic Chapters Index

 

Dodo (image assumed in public domain)

Dodo (image assumed in public domain)

 

In 1598 Portuguese sailors discovered a flightless bird on the island of Mauritius. The birds did not try to hide from the sailors since they had never encountered humans before. This made it easy to kill. The sailors called the bird the dodo (which is Portuguese for stupid or simple). By 1681 the dodo was extinct. All of them had fallen prey to human hunters or the carnivores, such as dogs, which the sailors introduced to Mauritius.


 

Elephant, Tanzania © Shirley Burchill

Animals are hunted for their fur, meat or other valuable parts of their bodies.

Elephants are hunted for their tusks which are carved into ivory jewellery. Rhinoceroses are hunted for their horns which are ground up to make traditional medicines in Asia.

Black rhinoceros, Kenya © Shirley Burchill

 

Parrots, Vincennes Zoo, Paris  © Shirley Burchill

 

Lion fish, Bristol Zoo, UK  © Shirley Burchill

Examples of organisms removed from tropical regions by humans - 
parrots, orchids and tropical fish.

Orchids, Northern Australia © Shirley Burchill

HUMAN INFLUENCES ON POPULATIONS

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The Extinction of Species

 

Passenger pigeon (image assumed in public domain)

Passenger pigeon (image assumed in public domain)

 

Two hundred years ago in North America there lived a bird called the passenger pigeon. At that time it was one of the most common birds in the world; there were thought to be 3 to 5 billion passenger pigeons. From 1860 to 1880 this bird was almost completely exterminated by hunting. By 1890 the bird had become rare and it was protected in several states. This protection was too late. The last wild passenger pigeon was shot in 1900 and the last passenger pigeon of all died in a zoo in 1914. The passenger pigeon had been exterminated. When all the individuals of a species have died, the species is said to be extinct.

Extinction is forever - the passenger pigeon will never be seen again. Each living organism which humans force into extinction is a tragedy for nature.

Humans sometimes cause the extinction of species deliberately. For example, humans may exterminate a species by hunting it, trapping it or over fishing it. The population of a species may become so small that it cannot recover. The example of the passenger pigeon is not the only one.

 

Fishermen © Shirley Burchill

Over fishing or excessive hunting by humans can reduce the populations of certain organisms on Earth.

 

Large predators may be exterminated because they kill livestock. Wolves are often hunted because they kill sheep. Wild animals and plants may be collected for sale as pets or for use in research. Many die when they are captured, while they are being transported or in captivity. For example, 128 million tropical fish were imported to the USA in 1980.

 

Wolves, Thoiry, France  © Shirley Burchill

Wolves, Thoiry, France

 

A reduction of the population of species is not always caused directly by killing the organisms through hunting or fishing. Sometimes human activities destroy the habitats of living organisms. The habitat of an organism is its home: where it lives, feeds, and reproduces. If an organism's habitat is a deciduous forest, for example, and humans cut down the forest to make farmland or build houses, the organisms living in the forest will die if they cannot adapt to the changes or find a new place to live. Many species have become extinct because humans have destroyed or modified their habitats, polluted their environment or introduced new species to an area.

 

The tiger's habitat is disappearing as humans clear the jungle  © Shirley Burchill

The tiger's habitat is disappearing as humans clear the jungle

 

 

 

 

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