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Part XVII : Human Influences on Populations Index

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

Topic Chapters Index

 

The Water Hyacinth

The water hyacinth originally came from the Amazon basin in South America. Today it is a serious pest in North America, tropical Africa and South East Asia. This plant was accidentally introduced by humans to these regions and it grew rapidly in the rivers and lakes. In certain parts of tropical Africa, transport by river boat has become impossible because this water weed has completely blocked whole river systems.

The water hyacinth © Paul Billiet

Map showing the progression of the water hyacinth indicating the dates which humans introduced the plant.

World map showing progression of the water hyacinth © Paul Billiet

 

The Starling

Humans are also responsible for the introduction of a bird called the starling from Europe to the United States. People brought them across the ocean to New York City's Central Park and set them free. As the population of starlings increased, so did competition with other bird species for food and nesting space.

African starlings © Shirley Burchill

Map showing the progression of the starling in the USA from 1918, when it was introduced, to 1949

Map showing the progression of the starling in the USA © Paul Billiet

 

HUMAN INFLUENCES ON POPULATIONS

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Introduced Species

Humans have helped to spread many species across the world. Plant species used in agriculture, for example, have been deliberately introduced to new areas by humans.

Sometimes wild animals are introduced for hunting as a sport. Exotic plants are grown in gardens and sometimes their seeds escape and colonize the surrounding area. Such animals and plants can spread rapidly because they have no natural predators in their new habitat. They compete with the native flora and fauna or kill them. In some cases, introduced species completely take over a habitat and eliminate the species who were living there originally.

Sometimes the introduction of species is intentional and beneficial for humans. Every major agricultural species has been introduced by humans to new regions of the globe: tomatoes, rice, wheat, potatoes, and many more.

 

Colorado beetle, Rats and Rabbits

Colorado beetle © Paul Billiet

 

More often, however, species are introduced accidentally and have a negative impact. The Colorado beetle was introduced to Europe from North America and has been damaging potato crops in Europe ever since. Rats originated from Asia and spread to Europe and the Americas as unwanted passengers on trade ships. The expansion of the Roman Empire was the reason for rabbits spreading north from Spain to the rest of Europe. Centuries later, in 1849, when Europeans were exploring the continent of Australia, rabbits were introduced and have caused serious problems ever since.

 

Rabbits  © Paul Billiet

 

 

As methods of transportation have increased in speed and intensified their traffic, humans have been more careful not to introduce harmful species to new regions. One group of organisms which people are especially concerned about are micro-organisms. Because bacteria, viruses and other germs are not visible, they can travel without being detected.

 

 

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