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9.5 Option – Introduced Species and the Australian Environment: 5. Rehabilitation
Extract from Earth and Environmental Science Stage 6
Syllabus (Amended October 2002). © Board of
Studies, NSW.
[Edit 6 Aug 08]
Prior Learning: Science Stages 4–5
syllabus: Outcomes 5.10c.
Preliminary Course 8.3 (subsection 5). 8.4 (subsections
1)
Background Information: When many of the plant and animal species were introduced to Australia the attitudes were different. People didn’t consider the damage they have on the environment, including the native species. Even today some nurseries sell plants that ecologists would prefer were not sold. Governments are now spending a lot of money on rehabilitation that could have been saved if some thought went into the original action.
explain what is meant by biological control
- A biological control is the introduction of one species
by humans to keep the numbers of another species low by
various methods, including preying on that species and
parasitising the pest species.
- Biological control usually does not result in the complete eradication of the target species but it reduces the numbers considerably so it is no longer considered a pest.
process information from secondary sources on the uses and successes of the various forms of biological control
- Collect information from a variety of sources, such as
the Internet, popular environmental journals and books on
environmental issues, on the successes and uses of various
forms of biological control. One good site to start with
is:
A plague on the pest
- rabbit calicivirus disease and
biological control, Australian Academy of Science,
Canberra.
- Use the Internet to find the Fact Sheet on
The Cane Toad (Bufo marinus) The Department of Environment, Water, Heritage
and the Arts, Canberra, ACT.
- Process this and other information to find some current
methods being researched in biological control.
- Process the information by arranging it in a table to show the Form of Control, Uses, and Successful examples.
describe the following types of biological control and give examples of the use of each:
- predator–prey
- bacterial/viral parasites
- release of sterilised males
Predator-prey
A predator species which feeds on the target is introduced . An example is:
- American wasp (Trioxys complanatus) was introduced in the late 1970s to control aphids that attack alfalfa. It lays its eggs in the aphid, the larva feed on and then kill the aphid.
Another example is:
- A weevil (Cyrtobagous salviniae singularis) was introduced from
South America in 1980 to control Salvinia.
Click here to see a photo of salvinia. CRC for Weed Management and the
Department of Environment and Heritage, Canberra
Eggs are laid singly in stem cavities that are produced by the adult feeding. Females lay one egg every 2-5 days over a 60 day period. Larvae feed on young terminal buds and enter the leaf bud tunnelling inside after 3-14 days of surface feeding. On average it takes 23 days for the larvae to develop. The weevil pupates in a cocoon that is in contact with living plants. Most cocoons are found below the leaves or within the root mass. This weevil works best in northern parts of Australia in warmer climates.
Bacterial/viral parasites
The release of diseases into populations can have a dramatic effect on the
numbers of a population. Natural resistance develops in the populations however
and a control but not eradication of the species results.
An example is:
- Myxomatosis was introduced via mosquitoes and fleas to the rabbit population
in 1950. In the first few years of its introduction 90% of populations were
killed. Since then the numbers have increased to about 60% of the plague numbers.
Calicivirus has since been used for rabbits. Go back to the web site referred to above. Australian Academy of Science, Canberra.
Release of sterilised males
- Sterilised males mate with females in some species
to the exclusion of fertile males.
- No young are born.
- CSIRO has a project to reduce the numbers of bush
flies by releasing sterilised males into the population
during the breeding cycle.
- A genetically modified form of the myxoma virus is being investigated. This form of the virus will induce sterility. This process is also called immunocontraception.
outline the criteria used to determine the conditions under which an organism can be used for biological control
- The organism must not upset any species other than
the intended target.
- Biologists study natural enemies of the pest
species to discover whether they will attack any
Australian species.
- The species must attack only the target.
- The species must be free of its own predators.
- The species must be able to disperse beyond its point of origin.
describe the history of control of prickly pear as an example of successful biological control
- Before 1925 Prickly pear covered 250 000 square km of Australia.
- It was introduced to Australia in the 1800s as a garden plant.
- It produces fruit which is readily eaten by birds, foxes, emus and other
animals and so is spread by the animals. Floodwaters are another means of
spread for seeds and plant parts.
- In 1925 a moth Cactoblastis cactorum was introduced to control
the prickly pear.
- The larvae of the moth spread quickly and so decimated the prickly pear
population that it is now only found in isolated clumps.
- The moth population then fell to a low level as its food supply had been
reduced.
- Cactoblastis cactorum remains a small but important population
in the Australian environment.
See photos of prickly pear growing in north west NSW Les Tanner, North West Weeds, Gwydir Shire Council, Bingara.
This
link shows you the caterpillars of the Cactoblastis cactorum that ended
the plague.
gather information from secondary sources to contrast the main features of the Bradley Method of bush regeneration with an alternative method
- Perform an Internet search looking for local
environmental organisations. Search on each site for
the Bradley method and you should be rewarded with
information similar to that listed below.
Ther is an excellent Internet article from the December 1983 issue of "Native Plants for New South Wales" (newsletter of the Association of Societies for Growing Australian Plants, ASGAP, NSW Region), Bush regeneration.
At the end of the article there is a reference list of books and internet
sites. Look in these for information on other methods that may be used.
-
Three principles to work the Bradley method are:
- always work from good to bad areas
- disturb the soil as little as possible
- allow the rate of regeneration to dictate the
rate of clearing.
- For the Bradley method and other methods a
knowledge of weed species is essential and people need
to tread lightly so as not to damage native seedlings.
The third Bradley principle requires patience. As the
weed areas get thicker you need to go slower to allow
for the regeneration. Another feature of the Bradley
method is that no replanting is done as the plants are
allowed to come back naturally.
- Other methods may involve techniques such as replanting in badly degraded areas, using herbicides to remove certain persistent weeds and erosion prevention such as laying down matting to keep the soil in place while plants regenerate naturally or while seedlings become established. Whatever technique is used some of the Bradley principles are often incorporated into the method.
process, analyse and present information about strategies being used to rehabilitate an ecosystem or minimise threatening processes
- Use the information below and gather other
information on rehabilitation so as to
process and analyse
information on several strategies. In your analysis
decide if you think one method is better than another
or if certain methods are more suited to certain
conditions.
- Present your information to the class as an illustrated talk. You may also decide to have a guest speaker to talk about the strategies he/she uses, especially if they are trying to minimise acknowledged threatening processes.
Some useful information
In 1976 the National Trust decided to use the Bradley method in one of its properties, the Blackwood Memorial Sanctuary in Beecroft, Sydney. The National Trust employed management, principles and techniques of the Bradley method to rehabilitate the bushland in the sanctuary.
The National Trust kept records of work done over the 4 year program and found that costs were approximately 10% of a conventional clearing method (clearing and mass planting) with equal or better success.
The Bradley method was also demonstrated to be effective in bushland regeneration after fire. In 1978, a fire burnt its way through the Warraroon Reserve in Lane Cove, N.S.W. Toni May and Joan Bradley advised on the methods to assist native regeneration.
Teams of weeders worked spasmodically in the area for the next 18 months removing the weeds and leaving as little soil damage as possible for the native plants to get established.
After about 2 years the native plants were competing with each other and out competing the weeds.
With a minimum of effort the Bradley method can be applied to many bushland areas which have been devastated by fire.
identify broadscale environmental impacts of one or more introduced species on a local ecosystem
One introduced species is Carp (also known as European carp) and the ecosystem it has impacted on is the freshwater (rivers and streams) ecosystem.
- Carp stir up the waterways disrupting the ecosystem
of the native fish, which need clear water to search
for their food.
- Numbers of native fish have been steadily declining
since the introduction of the carp.
The Murray River has displayed a steady increase in the numbers of carp since a strain was released in a tributary of the river in the 1960s but hopefully research and action will reverse that trend. See Carp.Save the
Murray, Venture, Innovation, Vision, Action, South Australia. The CSIRO and
the Murray Darling Basin Commission are also developing methods of reducing
carp numbers.
examine and critically evaluate the strategies being used to rehabilitate this ecosystem or to minimise threatening processes
- Three strategies are the introduction of the Rhabdovirus carpio that produces
the disease 'spring viraemia, a natural disease of the fish, the introduction
of commercial fishing for fertiliser supply (e.g. Charlie Carp fertiliser)
and the daughterless carp project of the CSIRO and the Murray Darling Basin
Commission, 2002.
- One problem with the effectiveness of the commercial fishing would be that
you would have to catch 90% of the fish to significantly affect the numbers
in the next generation. With the introduction of a virus as well and the daughterless
carp project, you may make inroads into reduction of the population.
- Another strategy would be to increase the breeding rates of the native fish
by returning the rivers as much as posible to the state before white settlement,
such as natural snags in the river and places for the fish to hide as well
as allowing the fish to migrate above the dams by creating bypasses. This
method is already being used in some areas. Improved river flows may
restore the numbers and diversity of native fish predators such as the Murray
cod, which may reduce the regrowth of young carp. See National Carp Taskforce ,
an initiative of the Murray-Darling Association.
- These strategies and any others you may find being used, need to be examined and critically evaluated to see if they are effective in minimising the number of carp in the ecosystem without harming other parts, including organisms, in the ecosystem.
extrapolate current level of effectiveness of the identified strategies to the future in terms of:
- costs
- sustainability of the ecosystem
- monitoring
- management of the program
Costs
- A program where a commercial product like
fertiliser (blood and bone) makes the environmental
program more effective and eventually profitable.
- Introduction of a biological control like the spring virus is very cost effective (providing it has been thoroughly tested).
Sustainability of the ecosystem
- Unless the waterways are returned to a more natural
state the ecosystem will not be sustained.
- Native species breeding areas, seasonal flows of the big rivers, and methods to bypass the dams can assist the regeneration of the ecosystem.
Monitoring
- Local fisheries, water resources authorities and community groups will need to be involved in the monitoring of changes in water quality and numbers and types of fish. A central authority, responsible for the collection and processing of the data will also be required.
Management of the program
- Government grants to community groups, such as the
Natural Heritage Trust, will assist in the management
of the program.
- State and federal authorities will need to be there
in an advisory capacity.
Natural Heritage Trust is a federally
funded grant program.
Information on carp can be found at NSW Department of Primary Industry,
Fisheries.
analyse information and use available evidence to make predictions about future effectiveness of identified strategies
- Given the above information and information
obtained on the Internet or by talking to government
officers such as Department of Agriculture officers you
should analyse the information to
predict the outcomes of a program to
control Carp. Generate some plausible explanations
which relate to the program.
- Using correct scientific principles you should predict a logical progression for the program discussing the future effectiveness of the program.
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