There
have been many types of Ecological disaster. In this article, I am
going to confine myself to disasters caused to Australian Ecosystems by
introducing other animals.
The most famous one was the introduction of the Rabbit. The Rabbits in Australia
are mostly descended from a deliberate introduction of a group of wild
Rabbits in Victoria in south eastern Australia. These were released in
the hope of starting a business selling rabbit skins.
This did actually happen, but there was nothing to stop the rabbits spreading to the rest of mainland Australia. Now we have billions.
They compete with the native animals, denude the landscape of
vegetation and severely reduce the potential carrying capacity of the
land for grazing animals like sheep and cattle.
After doing this
to the mainland, some early settlers actually introduced rabbits to Kangaroo Island. On Kangaroo Island they were killed off by the goannas
which went down the rabbit burrows and ate the babies. On the mainland
rabbits also had predators, but one of the main ones, the Wedge-tailed Eagle, was killed off in huge numbers in the mistaken belief that they kill lambs.
As
well as the disasters caused to land ecosystems there have been ones in
the water. The most obvious one was the deliberate introductionby the
government of European Carp to the River Murray. The Murray-Darling
River system is by far the most extensive in Australia.
The carp were
introduced to eat the weeds growing in the river. Now they have taken
over much of the river's ecosystem and severely reduced the numbers of
native fish.
In almost every
little waterway in my area there are to be found numbers of Mosquito
Fish (mostly Gambusia affinis). These were introduced by the government
to control Mosquitoes. Recent research suggests that they are not even
particularly good at this, and the large numbers of native species were
already controlling Mosquitoes very well. Now it is illegal to even
possess Mosquito fish.
Of course, not all the introductions were
done by the government. Guppies got into a system of underground
waterways in Western Australia. These have decimated the native fish
adapted to this environment. Aquarists need to be very careful to not
release any of their fish into waterways. They also need to be aware
that unexpected things can happen. Ponds can overflow. Normally we
would not expect fish to be able to get out of an aquarium into natural
rivers, but a friend of mine had a very nice Oscar. A sudden flood
came. My friend, together with his wife and baby spent the night on top
of their house while the water flowed through their house. Their Oscar
went out with the water. I n this case, the fish would not have
survived. It would have been swept out to sea and died, but there must
be cases where this type of unexpected event does put fish into
waterways they can survive in.
A ridiculous introduction
was the fox. They were brought to Australia so the upper class English
who were coming to Australia could enjoy their fox hunting.
Not
all introductions have been disastrous. The Prickly Pear Cactus got
into the state of Queensland where it was spreading at an enormous
rate. (The prickly Pear was introduced by the British Government with
the first fleet.) A moth was introduced, with the very descriptive
name; Cactoblastis cactorum. The caterpillars of this moth
totally devastated patches of the invasive weed in tropical areas . It
was not effective in cooler areas, but remains one of the most
spectacular examples of biological weed control.
Another government attempt at biological control was the introduction of the Cane Toad, Bufo marinus,
to control beetles in sugar cane. They failed to control the beetles
and are now spreading steadily through Australia, disrupting ecosystems
as they go.
Not all destructive introductions in Australia were of foreign species. There are several cases of native Australian Animals being taken to different places in Australia and causing destruction. Koalas were introduced to Kangaroo Island and increased to such an extent that they are killing off the Manna Gum trees.
There are large numbers of other examples of deliberate introductions that have caused havoc.
Steve Challis
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Ecological Disasters