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?
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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:
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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?