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Changing Ecosystems
Year 11 Biology
Unit 2 – Outcome 2
 Changes in an ecosystem may be due to:
– Regular events
– Irregular events
– One off events
Tides and seasons
Floods
Oil spill
 Changes in an ecosystem may be natural or
be due to human intervention
 The initial change may involve the living
community or the non-living surroundings
 Detecting changes in ecosystems requires
long term study.
 Instruments such as satellite mounted
sensors give us a picture of how
ecosystems are changing
Dark blue patch is
the arctic ozone hole
These photographs, taken in 1928 and 2000, show
how South Cascade Glacier in the Washington
Cascade Mountains has retreated over time.
Arctic
circle 1979
Arctic circle
2003
Red, orange, and brown
colouring indicate areas where
temperatures measured in
2000 are warmer than the
average temperature from
1951 to 1980. The scale
represents degrees in Celsius.
Negative numbers represent
cooling, and positive numbers
depict warming.
Human Impacts on Ecosystems
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Flood control (damming, levee banks)
Fire prevention
Agriculture (land clearing, irrigation, fertilisers)
Mining
Industry (generation of wastes)
Urbanisation (power generation, waste disposal,
water storage, transport)
 Introduction of exotic species
Human Impacts on Ecosystems
Introduction of exotic species
 Exotic species are non-native
 Impact includes
– Exotic species are effective predators on native
species
– Introduction of new diseases
– Competition for resources
– Changes to the environment
 Over all this causes displacement and loss
of native species
Human Impacts on Ecosystems
Introduction of exotic species into Australia
Rabbits
 Several dozen rabbits were brought to a
property in Victoria in 1856 for hunting
purposes
 There are now hundreds of millions
 One female can produce 30 kittens a year
 Rabbits compete more efficiently than native
species and as a consequence have
displaced many native species
Human Impacts on Ecosystems
Introduction of exotic species into Australia
Rabbits
 Control of rabbits:
– Myxoma virus released in 1950-51. Carried by
mosquitoes and rabbit fleas. Initially 99%
mortality in some areas but populations became
resistant.
– Rabbit calicivirus released in 1995. dramatically
reduced population from an estimated 300
million
Rabbit damage
Human Impacts on Ecosystems
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Introduction of exotic species into Australia
Cane Toads
Cane toads are native to South and Central
America
100 Cane toads were introduced in 1935 to control
beetles damaging sugar cane
The toads have no natural predators in Australia
and preferred not to eat the beetle they were
introduced to control
Their range is estimated to be increasing by 35km
per year
Creamy venom cause death to native animals
such as goannas, dingos, and snakes that eat
them
Current and
predicted Cane
toad distribution
(2004)
The federal government spend
millions each year trying to solve
the Cane toad problem
Human Impacts on Ecosystems
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Introduction of exotic species into Australia
Carp
European carp was brought to Australia in the
1870’s.
It escaped from Victorian fish farms into the
Murray-Darling system in 1960
Carp increase the turbidity of the water resulting in
sunlight not being able to penetrate
This results in plants and aquatic life not being
able to survive
They also increase the nutrient level of the water
resulting in algal blooms
Biological Control
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Using natural enemies (predators, herbivores,
parasites and disease causing organisms)
1. Classical biocontrol
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Introducing an offshore natural enemy
Success – Prickly pear numbers reduced by introduction of
cactus moth
Failure – Cane toads
2. Conservation biocontrol
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Use of naturally occurring agents
3. Use of biopesticides
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Use of naturally occurring agents such as bacteria and fungi
Biotechnology
 Biotechnology generally refers to
recombining DNA for a specific use
 Example 1
– Blocking conception in rabbits
 Example 2
– Single sex carp
 Block a gene involved in female development
Human Impacts on Ecosystems
Over harvesting
 Over-harvesting is an unsustainable use of
a biological resource
 It is important to know where and when the
species breeds, its rate of growth and time
of sexual maturity
 This will reduce risks of over-exploitation
Human Impacts on Ecosystems
Salinity
 Salinity refers to the
salt content of water or
soil
 Excessive salt
stresses native
species
Human Impacts on Ecosystems
Salinity
 Dryland salinity
– Australia naturally has high salt levels in the soil
– Native plant species have large root systems to absorb
water
– Little rain water reaches the ground water supply
– European settlement resulted in native species being
cleared and replaced with shallow rooted vegetation
– More water reaches the ground water and the water
table rises dissolving salt and bringing it to the surface.
The clearing of native
vegetation species for
agriculture and mining
has resulted in the
water table rising. As
it dose it brings the
historical salt deposits
to the surface. This
water can run into
streams and rivers or
form salt beds on the
surface causing
plants to die.
Human Impacts on Ecosystems
Salinity
 Irrigation salinity
– Irrigation water soaks
through the soil adding
to the ground water
– Water table rises
bringing salt to the
surface
– Irrigation water dries
and leaves salt at the
surface
Human Impacts on Ecosystems
Salinity
 Cost of salinity in Australia
– More than $130 million of agricultural production
is lost annually from salinity
– The area of salt affected land in Western Australia
is increasing at a rate of one football field per hour
– Increased salinity could cause the extinction of
approximately 450 species of native flora and 250
species of invertebrate water fauna in the
Western Australian wheat belt
– If salinity is not effectively managed within 20
years, the salt content in Adelaide’s drinking
water may exceed World Health Organisation
standards
Information from a government web site
Human Impacts on Ecosystems
Damming and diverting rivers
 Results
– Change of water
temperatures disrupting
breeding
– Wetlands dry out due to
lack of flooding –
habitat destruction
– Fish migration stopped
Dam with fish ladders and spillway
Human Impacts on Ecosystems
Damming and diverting rivers
Snowy River Scheme
 The Snowy Mountains Hydroelectric
Scheme was established in 1967
 99% of the natural flow of the river was
diverted at the Jindabyne Dam
 Habitats down stream were destroyed
 A restoration process began in 2002. Over a
10 year period the flow will be increased to
21%
The Snowy Mountains Scheme consists of:
- sixteen major dams
- seven power stations
- a pumping station
- 225 kilometres of tunnels, pipelines and aqueducts
Human Impacts on Ecosystems
Eutrophication
 Accumulation of dissolved
minerals in water
 Waste removal
 Farming runoff
 Algal blooms multiply in
nutrient rich water
 This reduces light levels
and causes aquatic
grasses to die which in
turn reduced oxygen levels
 Cyanobacteria algal
blooms produce toxins
Murray River Algal Bloom
Swan-Canning
Estuary Algal
Bloom
Natural agents of change
Fire
 Australia is a fire prone country and species
have had to adapt to this
– Mobile organisms flee
– Slower organisms burrow
– Plant strategies:
 Vegetative reproducers
 Obligate seeder
Pomonal – Grampians
bushfires 2006
The Elephants Hide –
The Grampians
20 months after the fire
Natural agents of change
Fire
2003 Canberra
 Vegetative reproducers
– Regrow from buds under bark or underground
stems
 Rhizomes - Bracken
 Epicormic shoots – Eucalyptus (bark burns poorly.
Epicormic buds are dormant until fire)
 Lignotubers – Gums (Underground stems)
Natural agents of change
Fire
 Obligate seeders
– Plant doesn’t survive but seeds do
– Seed coat or fruit splits in the heat allowing the
seed to germinate
Natural agents of change
Fire
2002
 Fire frequency
– Frequent fires will reduce diversity
– Obligate seeders need time to germinate and produce
their own seeds
– Controlled burns can not be too frequent
 Absence of fire
– Lack of fire means bushland areas can become
overgrown.
– Sunlight can no longer reach grasses. This can result in
loss of diversity
Natural agents of change
Fire
 Aboriginal use of fire
– Used for hunting and land management tool
– Low intensity fires to reduce litter build up
– Next to burnt patches they left unburnt areas
– Grass lands were preserved
– Greater biodiversity created
Succession
 Natural replacement of a community over time
 Primary succession
– A bare area is colonised by organisms for the first time
– Eg: Colonisation of larval flows or coastal dunes
 Secondary succession
– Occurs in areas that have been disturbed
– Eg: Abandoned paddock
– Pioneer species
 first species to become established
 Survive under harsh conditions and reproduce
rapidly (r-selection)
 Succession stops when a stable community is established.
– Known as the climax community
Primary Succession
Primary Succession of a bog
Secondary
Succession
Grassland with
secondary
succession
Restoration
 Personal level
– Recycling
– Composting
– Thoughtful water use
– Supporting conservation groups
 Council level
– Local clean ups
– Providing recycling facilities
Restoration
 State government level
– Sewage treatment
– Legislation to protect ecosystems
 Federal government
– Legislation
– Quarantine
– Funding
– Liaising industry and environmental groups