Invasive Species

What is an Invasive Species?

• A species that has been introduced or is not native to an environment

• Invasive species are generally harmful to the local habitat or native species

• Unwanted pest

More Examples of Invasive Species

• Grey squirrel• American beaver• Cane toad

Different Routes of Invasion

Most invasions are due to human activities:• Plant or pet trade• Commercial shipping• Tourism…and many other routes…

Quiz: What Characteristics Make A Good Invader?

• Rapid reproduction• Fast growth• High dispersal• Tolerant to many different conditions• Able to live off many different foods• Used by humans

The Impact of Invasive Species

• Ecological:– Reduce native biodiversity– Direct predation on local species – Spread of disease– Upset balance of local ecosystem

The Impact of Invasive Species

• Economical:- Very expensive - agricultural pests cause many £Bn of damage every year!- Very expensive to eradicate invasive species

Controlling Invasive Species

• Controlling invasive species once they have become established is difficult.

• Control is also usually very expensive! • There are four main ways that invasive species

are controlled:– Physical control– Chemical control– Biological control – Prevention

Physical Control of Invasive Species

Controlling plants:• Mechanical – excavation, strimming, etc.• Removal of plants by hand • Installation of growth barriers

Controlling animals:• Culling • Trapping and hunting• Putting up barriers or fences

Chemical Control of Invasive Species

• Chemical control involves applying poison to eliminate invasive species

• E.g. Eradication of rats on Henderson Island– Use rodenticide (rat poison)

• Insecticides & pesticides

to control insect pests• Herbicides (weed-killer)

to control plants

Biological Control of Invasive Species

• Uses a living organism to control invasive species• This organism may eat the invasive species or

cause it to become diseased • Biological control agents must be carefully

assessed before release to ensure the control species will not become invasive itself

Seven-spot ladybird Harlequin ladybird

Preventing Invasive Species

• Prevention is better than cure! • Preventing invasive species

from being introduced

somewhere in the first place,

or preventing them from

spreading if they do arrive,

is the key to avoiding

long-term harm to ecosystems

Barrow Island Case Study

• Barrow Island is a small island off the NW coast of Australia that is home to many species that have become rare or extinct on the Australian mainland

• This is partly due to a rigorous Quarantine Management System (QMS) operated by Chevron, which prevents invasive species from becoming established on the island

Activity: Case Files

• Pick a species from the invasive species suggestion list.

• Using the internet, books, journals and any other relevant materials, research your chosen invasive species and fill out a case file about the species and the problems it is causing outside its native range.

Activity: Case Files

• As part of the case file, you will have given your species an ‘invasive rating’ between 1 and 5. In groups or as a class, compare the species you have researched to other invasive species.

• Discuss how you would rank all of the species in terms of their invasive impact, starting with the species that has the worst effect on non-native species, habitats or ecosystems.

• Write down your list and remember to justify your reasons.

Optional discussion points and extension activities

• Research biological control of invasive species. Find examples of both successful and unsuccessful use of biological control agents and discuss the implications of introducing species that are not native to the environment. What are the potential costs versus the potential benefits?