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Exotic and Invasive Species

Introduction to the Issue

An exotic species is one which has been introduced to an environment which it is not meant to be in. These species can be animals, plants or diseases. Animals are considered invasive when they begin to cause economic or environmental harm. This article concentrates on animals with some small mentions of plants.

Invasive animals are often called pests and an invasive plant is often known as a weed.

This movement is one which has taken place thanks to humans and doesn’t apply to the establishment of vagrant species which make their own way to a new environment such as birds flying to a new land mass or fish swimming to new portions of the ocean.

Some species are introduced on purpose for positive benefits such as livestock for human food, others are introduced on purpose but have a negative effect such as cane toads in Australia which were introduced to control beetles that ate sugar cane and have since gone on to decimate populations of endangered species and others will be introduced accidentally such as mussels transferred on the hull on a ship.

Introduced species may also come to an area as a pet but be released if they become too big or difficult for their owner to care for. An example of this is the many large pythons which have been introduced to Florida in the United States.

Reticulated python

The reticulated python is an exotic species which has been introduced to Florida

Why is it a Problem?

These exotic species are new to the environment and as such this area is not adapted for dealing with them and has no defense against them. This applies both to the environment such as rocks, soil and trees and animals within this area.

In areas where these species are introduced they will often affect their environment by damaging soil such as by compaction by larger hoofed animals. In addition they may overgraze plants and outcompete other animals for their food.

Predatory animals have a direct affect by hunting for the native animals in an area.

Often introduced species come to new areas accidentally by sneaking on to ships or planes. They can establish in a country and go unnoticed until such a time that they begin to cause problems in their new home.

The worst outcome of an introduced species may be that they cause the extinction of a native species due to having such a large effect on the population.

New species can establish in large numbers. WWF estimates that 20 new pests or diseases establish in Australia each year.

One of the major problems which native animals present is that they will have few, if any predators in these areas making it easy for their population to rapidly expand and begin to outcompete other species.

Cats introduced to a South African Island grew their population from five in 1949 to 3,400 by 1977 causing harm to local birds and cane toads in Australia have grown their numbers from 3000 in the 1930s to 200 million today.

Not all exotic species are problematic. Many food crops are exotic to the area they are grown in and would not survive without human care such as fertilizer or additional water. They provide a benefit to the area by providing food for human consumption.

cane toad

The cane toad is an exotic species which was introduced to Australia

Is there a solution?

One of the main solutions is eradicating the organisms once they establish. When a population is detected works such as poisoning are undertaken to remove these animals before they reach large numbers. While this is unfortunate for the individuals involved it saves the lives of countless other animals which would be lost if they established. It is still important that any control method is humane and aims to reduce suffering to the invasive species.

While it is a major cost in areas where highly endangered species live a fence may be used to remove exotic species that prey on them.

The main way to prevent this issue is to stop exotic species establishing through measures such as quarantining items which are being moved from one country to another or washing down ships before they move from one country’s waterways to another.

What can you do to help?

There is a range of methods which you can use to prevent the spread of exotic species. Some ideas including making sure that you don’t buy plants which are likely to become invasive for your garden, don’t move an animal or plant from one environment to another and don’t release pets in to the wild.

Photo Credits


Public Domain


By Froggydarb, CC BY-SA 3.0,


WWF. 2020. Issues With No End In Sight. [online] Available at <> [Accessed 12 June 2020].

Minchin, D., 2020. Exotic Species – An Overview | Sciencedirect Topics. [online] Available

at: <> [Accessed 12 June 2020].

2020. Invasive Species In Australia. 1st ed. [ebook] Canberra: Australian Government Department of Environment and Heritage, pp.1-3. Available at: <> [Accessed 12 June 2020].

National Geographic Society. 2020. Invasive Species. [online] Available at: <> [Accessed 12 June 2020].

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