Stage 2 Biology – Ecosystems Notes
E10.
Human practices can lead to major changes in communities
·
Extinct – a species that can no longer be found
in the wild or has not been seen in the wild for many years
o
Normal natural occurrence due to environmental pressures
o
However, current loss of species is at its
highest level for 60 million years
o
Every hour, approximately 8 species become
extinct – around 10,000 times the normal rate
·
In Australia
o
Several groups that are more likely to become
extinct
§
Where each individual requires a large area for
its home (eg. Tasmanian tiger)
§
Mainly restricted to an island or small area
§
Specialised habitat requirements
§
Live in habitats that are rare due to land
clearance for agriculture/pasture/settlement
·
Human activities impacting on species
o
Pollution
§
Chemical pesticides/insecticides: DDT – widely
used to control pests; accumulation in tissues causes few problems until the
concentration rises; in higher order consumers, the levels are significantly
increased and have caused extinction of predatory birds as it interferes with
calcium metabolism (eggs have thin shells)
§
Oils spilled by tankers – death of birds, fish,
other marine life
§
Acid rain: Accumulation of sulphur and nitrogen
oxides from burning fossil fuels; mix with water vapour to form acids
(sulphuric and nitric); causes damage to lakes and forests due to pH levels
falling; buildings eroded; respiratory diseases
§
CFCs: Chlorofluorocarbons; used in aerosol
sprays/refrigerants; react with ozone – destruction of the ozone layer which
protects us from UV radiation
§
Heavy metal poisoning: Industrial plants produce
heavy metal pollutants such as mercury, cadmium and arsenic; kill soil
organisms; disrupt marine ecosystems; stormwater drains enter the oceans which
deposit oil, fertilisers, insecticides, detergents and other chemicals
§
Sewage: From partially treated sewage or
intensive animal farming; can lead to increased algal growth
§
Fertilisers and detergents: Run-off water
carrying fertilisers and detergents; leads to excess algal growth – destroys
other forms of life; nitrates and phosphates are essential for growth, but when
they are in excess, they act as a pollutant
·
Eutrophication – large amounts of nutrients
promote excess algal growth
§
Radioactive waste:Chernobyl – explosion occurred
as a nuclear reactor blew up, carried radioactive waste; large numbers of
people exposed; dumping of nuclear waste is also an issue – outback Australia
is suitable, but causes debate
o
Introduced species
§
Compete with native species for habitat and resources
or feed on them
§
Include: cats, dogs, foxes, rabbits, pigs,
donkeys, goats, cane toads, sparrows, starlings, trout, carp, salmon
§
In 1800s, cats were introduced to control spread
of mice and rats – by 1850, feral cats were established in the wild and have
spread – cope with a wide range of environmental conditions and have few
predators; used to eat rabbits, but now eat more native species; carry diseases
§
Rabbits – destroy native vegetation and compete
with native animals for resources; can take over bandicoot and bilby burrows
§
Feral pigs – damage to the ecosystems around the
edge of swaps
§
Australian herbivores such as kangaroos exert
little pressure on the environment, compared to introduced species like goats
that graze more heavily
§
Plants – compete with native grasses; are toxic
to some species; chokes waterways
o
Mining
§
Removes vegetation and topsoils – disrupts local
ecosystems
§
Pollutants can end up in rivers
o
Climate change
§
Release of carbon dioxide from combustion of
fossil fuels
§
Contributes to enhanced Greenhouse effect (this
is normal – it is what keeps the Earth warm enough for us to live on, but when
it is enhanced, the temperature rises)
§
Prediction that the average temperature on Earth
will rise by 3-4oC in the next 75 years
§
Results in polar ice melting, expansion of sea
water, rise in sea level that changes many terrestrial habitats; species move
to preferred climate
o
Harvesting
§
Fishing – sustainable if managed correctly, but
trawling and dredging kill huge numbers of species and lead to destruction of
the sea bed
o
Habitat clearance
§
Rainforest being destroyed to support economy
§
Forests are vital in absorbing carbon dioxide
from the atmosphere (reduces global warming)
·
Preserving habitat
o
Habitat is the main contributing factor to
extinction
o
When native vegetation is cleared, habitats for
native species are destroyed and the diversity of habitats is reduced
o
Reasons for maintaining natural vegetation:
§
Provide a range of habitats to maintain species
diversity
§
Provide vegetation with deep roots that maintain
water levels and help prevent salinity
§
Maintain and protect the soil from erosion
§
Absorb carbon dioxide and produce oxygen
§
Maintain rainfall patterns
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Reduce weeds and feral animals
o
Consequences of removing vegetation
§
Many birds require nesting sites only found in
mature trees
§
Chain reaction when species are threatened or
destroyed – related to predation, decomposition, pollination etc.
§
More impact of introduced animals
§
Loss of native grasses destroys a food source
and a natural habitat – conditions are ideal for opportunistic species to move
in and colonise; introduced species often take over leading to further
breakdown of habitat
§
Causes fragmentation of land – water and
nutrient cycling is impacted on, and results in decline in species diversity
§
Changes rainfall due to changes in convection
clouds
