16. Changes to Ecosystems

Chapter 16
Cabbage Tree Island
1. Read Pages 501-503 together and
2. Copy Figure 16.2 under heading
3. Define the terms endangered,
vulnerable and extinct.
4. Quick Check questions page 503 Qs 1-3.
Changes in ecosystems may
be due to:
Regular and predictable events (tides
and seasons)
 Sporadic events (floods)
 One-off events (oil spill)
 Primary changes in ecosystems may be
due to natural agents or to human
Changes in ecosystems
can be:
Short term
Long term
Irregular change
 Fire
 Cyclic changes: day/night, seasons, tides
 Continental drift
 Climate change
○ Deserts, ice ages, refuges
○ Causes: ocean currents, atmospheric change
 El Nino, tsunami, earthquake
Human Impacts on
Changes due to human intervention are
usually associated with economic gain and
meeting the needs of the growing
 They can include:
 Fire prevention
 Land clearing
 Flood control measures
 Introduction of exotic species, deliberately
or accidentally.
Human Impacts on
Introduction of exotic species
Over-harvesting: lack of
Waterways: damming, recreational
and waste pollution
Exotic species
Choose one
species to
Biological control
In each box:
Example of where it is occurring.
Important point(s) that need to be made.
Solution that we have reached.
Introduction of exotic species
Introduction of Exotic
Not all exotic species become major
ecological pests. E.g. cereal and fruit
 However, when some exotics are
introduced to local ecosystems,
displacement and loss of native species
usually occurs.
Exotics in Australia
Key term: Biological control
Is the use of a natural predator or parasite to limit the population of a pest
For example, prickly pear is successfully controlled by the moth Cactoblastis
cxactorum. The cane toad was introduced to control cane beetles but became a
pest species itself.
Impacts of invasive exotic
How do natives become lost or
 When introduced species are successful
predators of native species (feral cats
and foxes).
 New diseases are brought in which natives
are not resistant to (fungal diseases).
 Exotics use the same limited resources as
 Exotics change the environment of an
The introduction of rabbits began with
several dozen brought to a property in
Victoria in 1859 for hunting. They
quickly spread to New South Wales,
Queensland and the west by the 1900’s.
 They have a high reproductive rate; one
female can produce 30 kittens a year.
 In their natural environment, their
numbers are controlled by food
shortages in winter and the presence of
predators, parasites and competitors.
Rabbits compete more efficiently
than native species for food and have
displaced many native species.
 Many attempts have been made to
control numbers:
 Myxoma virus (killed many rabbits
however rabbits become resistant to the
 Calicivirus (causes hemorrhagic disease
and numbers have dramatically reduced).
Cane Toads
Cane Toads
Originally from South and Central
America, 100 toads were brought to
Queensland to control greyback beetles.
 Cane toads have now spread and are
estimated to be increasing by about 35
km per year.
 They have few natural predators in
 They secrete venom from glands and
cause the death of many native animals.
Carp were brought to Australia and
escaped from the Victorian fish farms
into the Murray-Darling River system.
 They feed at the bottom of water. They
take up mouthfuls of mud, spit it out so
that the material becomes suspended in
the water, then swallow particles of
organic matter or small organisms.
Because of this behaviour, they
destroy water plants and change
aquatic habitats. Sunlight cannot
penetrate through, thus some plants
are lost from the aquatic environment.
 Carp excretions increase the levels of
dissolved nutrients leading to algal
blooms (and eutrophication).
Over-harvesting is an unsustainable use
of biological resource.
 Harvesting of any species must be
carried out at sustainable levels that
allow the species to recover its numbers
naturally between harvesting.
 Important biological knowledge to
prevent over-exploitation includes:
 where, when and at what age a species breeds
 its rate of growth
 the time required for sexual maturity.
Salinity refers to the salt content of
water or soil at a level where the salt
content damages soil and degrades water
 Salinity causes economic loss through
loss of productive agricultural land and
damage to roads and buildings and puts
the supply of acceptable drinking water
at risk.
Dry land Salinity
Soils over much of Australia have
naturally high salt levels and this salt is
stored below the soil surface.
 Because of Australia’s low rainfall, high
evaporation rates and flat terrain, this
salt has not been washed away but has
been absorbed into the soil.
Dry land Salinity
The natural vegetation in Australia has
deep rooted trees. These take up large
amounts of water from the soil and this
water is lost by transpiration.
 Under these conditions, the water table
has remained at a constant depth below
the surface.
 Since European settlement, native
grasslands have been cleared for urban
development and the deep-rooted trees
have been replaced with shallow-rooted
Dry land Salinity
As land is cleared, more water enters
the soil and reaches the ground water,
causing the watertable to rise.
Dissolved salts are brought up to the
surface and it causes many plants to
Dry land
Irrigation Salinity
Irrigation Salinity
This occurs when excess irrigation seeps
into the soil, causing the watertable to
 Eventually the watertable reaches the
root systems of plants and those they
are not suited to salt are killed.
 When the irrigation stops, the soil dries
out and salt is left at the surface.
 The surface soil gets more and more
salty the more often the process is
Waterways: damming and pollution
The damming of rivers and
diversion of water from rivers
The health of river systems depend on
natural water flow to maintain their
biodiversity, if not the following may occur:
 The release of cold water from the bottom of
dams can lower water temps to a level where fish
can no longer breed
 Wetlands that depend on periodic flooding may
begin to dry out and populations of native fish and
water birds may decline
 Movements of native migrating of river fish stop
or slow with many species becoming extinct.
Nutrient overload
Nutrient Overload
The accumulation of dissolved mineral
nutrients in a body of water is termed
 Cyanobacteria can multiply rapidly and
form a bloom that covers much of the
water surface. As it spreads it reduces
the light intensity in the water depths so
that submerged plants die and the
amount of organic matter in the water
 Decomposers feed on the organic matter
and multiply and use up the dissolved
Genetic Modification
Genetic Modification (GM)
Genetic modification is the use of
modern biotechnology techniques to
change the genes of an organism, such as
a plant or animal.
 GM is used because it can change the
genes of an organism in ways not possible
through traditional breeding techniques
providing opportunities for new plant
varieties and animal breeds.
Genetic Modification (GM)
An example..
 Products from GM soybean, canola, corn,
potato, sugar beet and cotton crops have
been approved for use in food in Australia.
These crops have been modified to be insect
resistant, herbicide tolerant or both.
What are the advantages and disadvantages
of these crops?
Advantages and Disadvantages
of GM
 GM crops that have been modified for
insect resistance or herbicide tolerance
allow farmers to use less herbicide and
pesticide on their farms.
 These crops can grow without the impact
of insects/herbicides meaning a stronger
food economy for Australia.
Advantages and Disadvantages
of GM
 If too much herbicide is used it can
contaminate the soil, therefore
impacting on other crops surrounding the
GM products.
 Weeds etc can become tolerant to the
use of herbicides therefore the
herbicide will not be effective any
Natural change agents: Fire
Species living in fire-prone ecosystems
must be capable of surviving the effects
of fires, either as individuals or through
their offspring.
 Mobile organisms escape by flying or
running away.
 Slower animals escape by retreating into
 Soil is a good insulator.
Natural change agents: Fire
Plants cannot escape but have survival
 Vegetative reproducer
 Obligate seeder
Vegetative Reproducer
Vegetative Reproducer
Plants using this method regrow through
means of buds found in the bark or in
underground stems; e.g. Eucalyptus.
Obligate Seeders
Obligate Seeders
They don’t usually survive bushfires,
however their seeds germinate in the
mineral-rich soil that is produced by
Fire Frequency
After bushfires, the native plant
population can either be replaced (OS)
or can regenerate (VR).
The interval between fires can affect
the diversity of a plant community.
If fire occurs frequently, some species
may be lost.
If it remains absent for a while, certain
animals and plants will die as they rely on
the new shrubs as a resource.
As a result, controlled burns often take
place to ensure the biodiversity remains.
Succession is the natural replacement over
time of one community by another
community with different dominant species.
Primary succession occurs in areas that have
not been previously colonised. E.g. by lichen
on a bare rock.
Secondary succession occurs in areas that
were once colonised but have been
disturbed. E.g. by clearing for farmland,
then subsequently abandoned and
A climax community is a stable community of
consistent composition.
Stuff to do
1. Read page 528 – 534
2. Complete quick check
questions page 533 & 534

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