E10 Summary

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

§  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