1. Invasive Species
Introduce the session - today we are going to look at invasive species.
We will talk about:
What an invasive species is, and how it differs from introduced species
Some examples of invasive species
What characteristics make a successful invader
Different ways invasive species can be introduced to the environment
Impact of invasive species on the environment
Ways to control invasive species
Successful case studies, including a focus case study on Barrow Island, Australia
Research activity and preparation of invasive species case files
Images (L-R): a Cuban treefrog (Osteopilus septentrionalis), a very successful predator and invasive species; a common carp being fed on by an invasive species in British waterways, the American signal crayfish (Pacifastacus leniusculus); Giant African snail (Achatina fulica)

2. 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
Ask the class: “What is an invasive species?”
A species (plant/animal) that has successfully established itself outside the range it is normally found in. Rabbits (Oryctolagus cuniculus) were introduced to Britain by the Normans in the 12th century and continue to thrive today.
Both invasive and introduced species (also know as alien, exotic, non-native or non- indigenous species) will generally have arrived outside their native distributional range as a result of human activity (either deliberate or accidental). However, whereas ‘introduced species’ is a general term for species that live outside their native range (encompassing those species which may have no negative effect on the environment, those that may be beneficial to the environment and those that have a damaging effect on the ecosystem), the term ‘invasive species’ invariably only applies to species that are considered harmful to the biodiversity of the local habitat or to native species.
Invasive species often outcompete resident species for food and other resources.
Invasive species can also have a direct effect on native species, as in the case of the introduced black rats (Rattus rattus) on islands with nesting seabirds. Rats will predate on eggs and chicks, which can drastically reduce the seabird population.
Many invasive species are also considered pests by farmers. The giant African snail (Achatina fulica) naturally occurs in East Africa but has been introduced to other areas of Africa, Asia and Australia where it feeds on crops, causing a huge amount of damage.
Read more about making the distinction between alien and invasive species: invasive-species/

3. More Examples of Invasive Species
Grey squirrel
American beaver
Cane toad
Here are some of the more well-known examples of invasive species:
The grey squirrel (Sciurus carolinensis), which was introduced to the UK from America, has displaced the native red squirrel (Sciurus vulgaris) throughout much of its range. It has done this by outcompeting the red squirrel for food resources. Grey squirrels are also carriers of a disease called the squirrel parapoxvirus, which doesn’t affect the health of grey squirrels but is known to kill red squirrels.
The American beaver (Castor canadensis) has been introduced to eastern Russia and Argentina, South America. Introduced beavers can cause problems by damming up rivers and felling trees, damaging the forest.
The cane toad (Rhinella marina) was deliberately introduced to Australia in 1935 to control another pest (a beetle that fed on sugar cane, a valuable crop). It didn’t, and has spread dramatically since, displacing native toads and poisoning animals that predate on them, such as the northern quoll (Dasyurus hallucatus).

4. Different Routes of Invasion
Most invasions are due to human activities:
Plant or pet trade
Commercial shipping
Tourism
…and many other routes…
In most cases of invasive species, human actions are to blame for their rapid spread.
Seeds that are imported from far away can grow and multiply rapidly in the wild to establish an invasive population. For example, Japanese knotweed (Fallopia japonica) has spread across the UK, outcompeting several native plants for space and light. Similarly, animals that are considered desirable pets often escape and establish feral populations, such as the rose-ringed parakeet (Psittacula krameri) in Richmond Park, London.
Ships move all over the world and have spread rats, mice and many other invasive species to numerous islands, which often has devastating effects on these islands’ biodiversity, and a particularly negative effect on nesting seabirds. Island species are very vulnerable to the threat of invasive species as many islands, such as Australia, New Zealand, Madagascar, the Hawaiian Archipelago, and the Galapagos have a high proportion of endemic and highly specialised flora and fauna which have evolved in isolation over hundreds of thousands of years. In the past, the geographic isolation of these islands has limited immigration of new species, allowing established species to evolve with few strong competitors and predators; however, with the advent of global travel and tourism, the transport of species from all over the world (both accidental and deliberate) has resulted in the introduction of invasive species to ecosystems that are often unable to cope. Islands are more prone to invasion by alien species because of the lack of natural competitors and predators that control populations in their native ecosystems. In New Zealand for example, the introduction of non-native species has caused an irreversible decline in many of the islands’ bird species, such as the kakapo, the world’s only flightless parrot.
Water discharged from ships can potentially transport a huge amount of invasive species. Numerous invasive species are thought to have spread this way, including the zebra mussel (Dreissena polymorpha) and Chinese mitten crab (Eriocheir sinensis).
Seeds of invasive plants can be transported hundreds of miles by cars, on clothes and under shoes. Areas that are visited more often by tourists are more likely to be at risk from the introduction of invasive species.

5. 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 ?
Ask the class: “What sort of characteristics make a species a good invader?”
Species which breed faster are better able to establish viable populations - e.g. rabbits (Oryctolagus cuniculus)
Species that grow faster are generally better able to outcompete others and take advantage of resources – e.g. grey squirrel (Sciurus carolinensis)
Species which are able to disperse seeds over great distances are likely to be better invaders - e.g. Japanese knotweed (Fallopia japonica)
Being naturally able to tolerate a wide range of environmental conditions allows for more invading potential
Not being a fussy eater allows a species to find food from many different sources e.g. black rats (Rattus rattus)
An association with humans is often the cause of a species becoming invasive. Many invasive species were introduced deliberately for food, fur or as biological control - e.g. cane toad (Bufo marinus)

6. The Impact of Invasive Species
Ecological:
Reduce native biodiversity
Direct predation on local species
Spread of disease
Upset balance of local ecosystem
Invasive species have a number of different impacts on local habitats and species:
Ecological factors include -
Reduced biodiversity – one invading species can displace a large number of native ones, e.g. Japanese knotweed (Fallopia japonica)
Direct interactions with native species (predation, parasitism, etc.) e.g. black rat (Rattus rattus)
Invasive species can bring diseases with them (an example being squirrel pox) that local species are more vulnerable too.
The complex and often delicate balance of many ecosystems is easily disturbed by invasive species, e.g. American beaver (Castor canadensis) deforesting areas and changing water flow.

7. The Impact of Invasive Species
Economical:
Very expensive - agricultural pests cause many £Bn of damage every year!
Very expensive to eradicate invasive species
Economical factors include -
Agriculture is a massive worldwide industry. Invasive species that feed on crops cost nations vast sums of money.
Programmes to eradicate or control invasive species are often costly and are not always successful.

8. 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
Controlling invasive species once they have become established can be difficult, and in some cases it may even be impossible.
Control is also usually very expensive!
There are four main ways that invasive species are controlled:
- Physical control
- Chemical control
- Biological control
- Prevention
These will be discussed in more detail on the slides to follow.
Image: A team of conservationists clearing Pleomele halapepe stand of invasive plants.

9. 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
Controlling invasive plants:
There are a number of approaches to physically controlling an invasive plant species. These can range from mechanical excavation or hand removal to the installation of growth barriers to suppress or stop invasive plants encroaching onto a site.
There are many things to consider when choosing an appropriate control method, and a single control method will not work for all species. For example, strimming plants can be effective in controlling some species, such as Himalayan balsam, but only if it is done to young plants before the seed heads have developed. Strimming would not be effective for woody species, such as rhododendron, as it does not affect root growth. Similarly, for species such as Japanese knotweed, strimming would result in the plant fragments being dispersed over a wide area, exacerbating the problem.
Controlling animals:
Culling – e.g. culling of the red deer in the UK to restrict the damage it causes to forestry, agriculture and the natural environment (e.g. browsing red deer (see photo) can prevent the regeneration of woodland)
Trapping and hunting
Putting up barriers or fences
Image: Red deer (Cervus elaphus) feeding on tree leaves. Red deer are native to most of Europe, southwest Asia and North Africa; however, it has been introduced to Australia, New Zealand and Argentina, as well as a range of other countries, where it can cause serious damage to native species and habitats. Even in the UK, red deer are periodically culled to prevent the population becoming out of control

10. 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
Chemical control of species:
Eradication – e.g. removal of rats from islands where they are having devastating effects on nesting seabirds. A large scale eradication project was recently carried out on Henderson Island to protect the native seabirds such as the Henderson petrel, whose populations were in serious decline.
As rats are extremely prolific breeders, the only feasible way to achieve the eradication of the species on a large and rugged island such as Henderson is by spreading bait containing a rodenticide (rat poison).
On Henderson, Brodifacoum, the active ingredient in many household rat poisons, was used to eradicate the rats.
Video – rat predating on Henderson petrel chick:
Find out more about the eradication of rats from Henderson Island: &

11. 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
Biological control uses a living organism to reduce or eliminate the population of the invasive species.
The organism may eat the invasive species or cause it to become diseased - it relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also involves an active human management role.
Control agents are often brought from the original habitat of the invasive species.
Images – L: seven-spot ladybird; R: harlequin ladybird – feeding on aphids
Ladybirds are often used as biological control agents to control aphids in greenhouse production of crops. Ladybirds are natural predators of aphids, and so one way of controlling aphid numbers is to release more ladybirds into an area to help control the aphid infestation. Depending on the level of pest infestation, as many as 5,000 to 200,000 ladybirds per acre (1 to 50 per square metre) per week could be mass-released.
However, biological control is risky. Proposals for biological control must be carefully assessed to ensure the control species does not become invasive and cause as much damage as the species to be controlled. One example of this is the harlequin ladybird. The harlequin ladybird spread to the UK after being imported from East Asia to Europe for commercial pest control of crops, and it is now affecting populations of the UK’s native ladybird species, as it is bigger than native species, better protected and able to outcompete native species for food resources.
Seven-spot ladybird
Harlequin ladybird

12. 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

13. 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
Chevron Australia has operated the largest onshore oilfield in Australia on Barrow Island for more than 45 years. Despite this significant activity, the island’s unique biodiversity remains intact and the ecosystem remains essentially free of exotic plants and animals due to a rigorous Quarantine Management System (QMS).
The unique environmental values of Barrow Island are linked to the presence of plant and animal species, particularly mammals, which have become rare or extinct on the Australian mainland. The 234 km2 island is home to 378 plant species, more than 2,200 invertebrate species, 13 mammal species, 119 resident and migratory bird species, and 43 species of reptile.
The species present on Barrow Island have been isolated for 8,000 years since rising sea levels separated the island from the Australian mainland; their survival on the island is due to the continued absence of the introduced predators and competitors present on the mainland and other islands in the region. The waters surrounding Barrow Island are protected as a Marine Conservation Area, within which the species richness of Barrow Island Marine Park rivals that of the Great Barrier Reef.
As the world’s largest non-government quarantine initiative, the QMS dwarfs the quarantine efforts of many authorities and states, addressing quarantine management pre-border (before goods and personnel reach the island), at the border (on arrival at Barrow Island) and post-border (outside of the development site) and implementing design and procedural innovations, including:
• Unique quarantine designs for buildings, containers and trailers to reduce the risk of contamination and facilitate cleaning and inspection.
• Shrink-wrapping non-containerised / crated cargo to prevent cross-contamination during transit and storage.
• Replacement of timber by plastic and replacement of other high-risk materials with alternatives wherever possible.
• Purpose-built airline check-in, screening and departure lounge for flights on dedicated aircraft from Perth to Barrow Island.
• Construction of dedicated mainland supply bases with quarantine storage, treatment and cleaning facilities.
• Dedicated marine loading and offloading facilities on the mainland and the island.
• A government licensed Quarantine Approved Premises to enable Barrow Island to be a ‘first port of entry’ for goods arriving from overseas, providing containment and treatment facilities, including the world’s largest washdown bay to accommodate gas plant modules shipped from overseas fabrication yards.
• Fumigation of all containers and wrapped packages to eradicate any invertebrates not previously detected.
This is partly due to a rigorous Quarantine
Management System (QMS) operated by Chevron,
which prevents invasive species from becoming
established on the island

14. 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.
To finish the activity, students should then use the information they have collected on the species to give the species an ‘invasive rating’. Based on their research and observations, students should fill in the assessment section of the case file, discussing the extent to which their species is causing a problem for the ecosystem that it has invaded. Students should attempt to give the species an ‘invasive rating’ using a scoring system between 1 to 5, based on how serious this species is impacting native species and habitats and how hard it is to control (1 = species is not very invasive and/or is easy to remove, 5 = highly invasive and/or difficult to eradicate). Based on their research, students should also suggest whether there are any additional management or control measures that could potentially be appropriate for their species.

15. 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.

16. 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?