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9.5 Option – Introduced Species and the Australian Environment: 3. Why introduced species become pests
| Syllabus
reference (October 2002) |
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3. Identification
of the conditions leading to introduced species becoming pests |
Students learn to:
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Students: |
Extract from Earth and Environmental Science Stage 6 Syllabus (Amended October 2002), (C) Board of Studies. NSW.
[Edit: 6 Aug 08]
Prior Learning: Science Stages 4–5
syllabus: Outcomes 5.10 (content 5.10c).
Preliminary Course 8.3 (subsection 5). 8.4 (subsections 1).
Background: Many successful introduced species have adaptations or environmental conditions suitable to the spread of their species in Australia. Identification of these factors is the first step to reducing the movement of introduced species within the country and hopefully reducing their numbers considerably.
gather, process and analyse information from secondary sources and use available evidence to identify the features of the named introduced plant and animal
- Gather information from the case studies below or look on other Internet sites. You could also look in books on Australian environmental issues or in popular and scientific magazines and journals.
- Process the information obtained by putting it in a table and incorporate this information with the information gained for the dot point below.
- Analyse the information that has been organised into a table, to identify the features of the introduced plants and animals.
assess the relative contributions of the following conditions to one named introduced plant and one named introduced animal becoming pests:
- suitable habitat
- suitable climatic condition
- range of food resources
- relative lack of natural predators/grazers
- high reproductive capacity
- well-developed dispersal mechanisms
- Choose the same animal and plant chosen above.
- View each of the case studies below or another animal or plant that you have tabulated to identify the features of the organisms that enabled them to become pests. The features are usually biological features of the organisms themselves.
- You can then assess the environmental conditions to judge which condition or conditions were the most important in contributing to the success of the introduced species.
- Once again organise the information into a table like the following example:
| Name of species | Features of the organism that led it to become a pest | Conditions that helped the organism to become a pest |
|---|---|---|
Although four case studies are given below, you only have to study one plant and one animal.
CASE STUDIES
The Rabbit
The history of introduction.
Twenty four wild rabbits, Orctolagus cuniculus were introduced to Australia, in 1859. They were released on the property of Thomas Austin of Winchelsea, Victoria for sport hunting.
The environmental conditions leading to the organism becoming a pest
- There were no natural diseases or large enough numbers of predators to prevent the success of the rabbit.
- The range of rabbits is limited by a need for suitable soils in which to dig their warrens. So they are rare in cracking clay soils.
- Rabbits do not appear to live north of the tropic of Capricorn as they don’t do as well in the higher humidity.
- Australian temperatures and rainfall are suitable.
Dispersal techniques
By 1886 rabbits had spread as far as the NSW/ Queensland
border. They did this by slowly moving north looking for food and with the assistance
of people moving them and releasing them. By 1910 they had covered their present
range. 
Department of Environment and Heritage. Scroll down to History.
Reproductive capacity
A rabbit is sexually mature at three to four months. They can produce litters of three to four young once a month given cool temperatures and fresh grass.
Control strategies
- Climate, predators and parasites have had minimal impact on numbers
- Conventional methods include exclusion fencing, ripping of warrens, fumigation of warrens and poisoning.
- Diseases such as myxomatosis and Rabbit Calicivirus Disease have been introduced into populations. At first over 90% of the rabbits died but the ones that had resistance passed this on to their offspring and now only 60% of rabbits that contract Myxomatosis die. Myxomatosis requires an insect vector and as such is limited by the range of the insect. A Spanish flea has recently been introduced into the rabbit population to carry the disease into the arid regions of South Australia.
Environmental impacts
- Rabbits compete with native wildlife for food and shelter. Small ground dwelling herbivores are the worst affected
- They compete with livestock for food.
- They eat plants to below ground level.
- By eating seeds and seedlings new generations of trees and shrubs are not grown so they contribute to the degradation of the soil.
- Over grazed paddocks cannot be managed by farmers when the rabbit is present.
Environment
Australia , Fact Sheet, Invasive Species - Rabbits are Weeds Too!
Cane toad Bufo marinus
The history of introduction
Cane toads were introduced to Queensland in 1935 to control an infestation of two species of cane beetles. The toads had little effect on the beetles which were eventually controlled by a pesticide.
The environmental conditions leading to the organism becoming a pest
- No natural predators or parasites in Australia.
- They were adaptable to a wide range of habitats.
- Cane toads now occur in a density ten times that of their homeland Venezuela.
Dispersal techniques
Cane toads are spreading south, west and north-west at a rate of 30 km per annum. They move along waterways and overland. Animals that try to eat them are poisoned and usually die.
Reproductive capacity
They lay up to 40 000 eggs in long strands
in shallow water. They have a very high success rate as most turn into tadpoles.
They are restricted to habitats close
to water for breeding but travel long distances away from water when not breeding.
Control strategies
- None at this stage.
- Viruses found in Venezuela kill tadpoles of toads but also native species.
- Two fungal pathogens have been discovered but more research is needed.
Since 2001 CSIRO has been conducting research into developing a biological control for cane toads. The goal of the research is to interfere with the metamorphosis of the cane toad to prevent it from maturing and reproducing.
Environmental impacts
- Toxic to predators.
- Studies by CSIRO Wildlife and Ecology found the toad had an effect on most native species and introduced animals. Even crocodiles that have eaten them have died.
Lantana species (there is more than one species)
The history of introduction
- Lantana is a weed of the world, introduced from the Americas. It grows from latitude 45N to 45S.
- Lantana was first identified in Australia at the Botanical Gardens in Adelaide in 1841and was noted around Sydney in 1862. It was introduced as a garden plant.
- Twenty nine different forms of lantana are listed as naturalised in eastern Australia
If you have had the fortune not to have come across
lantana and don't know what it looks like
click here to see a photo of some lantana plants, courtesy of Eurobodalla
Shire Council, NSW web page. If you want to read about lantana as a problem
weed in Eurobodalla Shire click
here.
The environmental conditions leading to the organism becoming a pest
Lantana prefers moist tropical, subtropical
and moist temperate zones of the world. This makes it particularly suitable
to the coast of eastern Australia.
Our many native and introduced bird species
find the fruit edible and as such spread the seed in their droppings.
Dispersal techniques
- Each flower cluster produces up to 20 soft purple to black fruits which are attractive to birds.
- The seeds are readily dispersed in the bird’s droppings.
Reproductive capacity
The abundant fruits produced by the plant and the asexual reproduction induced when the plant is slashed or burned are significant factors in the plant’s success.
Control strategies
- Chemical control by a herbicide such as glyphosate (Roundup) is effective as burning slashing and digging results in regrowth.
- " Find native plants which can compete with it and produce a shade canopy to reduce it from spreading.” says Dr Duggin, University of New England, NSW.
- Twenty six different biological species, mostly insects, have been released in Australia to destroy lantana, often with little success.
- The genetic diversity of lantana is a limiting factor in the control of the weed using biological control agents. In Queensland several rust pathogens, (fungi) have been successful with several of the main types.
Environmental impacts
- Lantana releases a chemical which inhibits the growth of native colonising species.
- Any disturbance to a forest canopy can be the trigger for establishment.
- Removal of understory and shrub layer increases the rate of establishment.
- Lantana infests four million hectares of land from the Daintree Rainforest to south of ulladulla.
- Lantana is shade tolerant and so can become an understory in open forests.
- Toxic - Causes photosensitivity in cattle.
- Breeding area for pigs, rats and insects.
- Causes a reduction in the natural diversity of plant species.
Salvinia species
Click here to see a photo of salvinia. Eurobodalla Shire Council, NSW .
The history of introduction
Introduced as an aquarium plant in the 1970’s.From aquariums it escaped or was released into the waterways.
The environmental conditions leading to the organism becoming a pest
Conditions in the north of Australia are ideal for the growth of salvinia as it likes warm water and high levels of sunlight.
Dispersal techniques
- An environment which has wet seasons that allow the plant to be carried in flood from one river system to another is ideal for dispersal.
- Dispersal is purely by vegetative means as the spore sacks are nearly all empty.
Reproductive capacity
Reproduces asexually.
Control strategies
Successfully controlled by a small weevil (Cyrtobagus singularis) since 1980 in warmer waters but the weevil has not been successful in cooler waters. In Mt Isa the local water supply, Lake Moondarra was inundated with the weed. Once the weevil was introduced, 50 000 tonnes of the weed were consumed in ten months.
Environmental impacts
- Suffocates the waterway by growing from bank to bank.
- Reduction in water weeds, oxygen levels and water quality.
- Blocks access to the waterway.
- Kills fish by reduction of oxygen exchange with the surface.
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