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Energy is transferred in a  one way flow through an ecosystem

• energy enters an ecosystem when green plants trap radiant energy from the sun by the process of photosynthesis

            carbon dioxide + water è glucose + oxygen + water

• energy is passed on from one organism to another via food chains

• energy is lost from the ecosystem via the process of respiration that releases energy from the glucose molecules to enable metabolic reactions to take place

            glucose + oxygen è carbon dioxide + water

• most energy is “lost” in the form of heat (metabolism)

• any habitat that does not have photosynthetic plants must “import” its energy from a habitat that does – energy is not recycled

  • e.g. caves (bat guano), bottom of a muddy lake (detritus – leaves and decaying animals that fall to the bottom of the lake)

• only approx. 1% of light that falls on plants is converted into biomass

• only approx. 10% of energy in the form of biomass is passed on to the next trophic level

• these are estimations only – a lot of variation exists due to

  • the life-span/reproductive cycles and metabolism of organisms,

  • the nature/complexity of the food webs in each ecosystem,

  • how much effort/energy has to be invested in “life processes” e.g. obtaining food, defending territory, evading predators, migrating, reproducing

Matter is recycled in an ecosystem by inter-connected water, carbon, oxygen, nitrogen and phosphorous cycles

• water cycle

• carbon/oxygen cycle

• nitrogen cycle

• phosphorous cycle

Mechanisms of change in an ecosystem

• succession is the progressive change in an ecosystem as one community alters the environment and “makes way” for other species until a climax community is established

  • particularly prevalent after natural or man-made disturbances to an ecosystem e.g. bushfire, volcanic eruption, clearing of native vegetation

• eutrophication is the process whereby nutrients are built-up in an aquatic environment resulting in algal blooms and subsequent depletion of oxygen

  • inappropriate use of fertilisers that run-off into water ways are a significant factor

Human Impact 

• introduced species

  • plants - weeds & crops

  • rabbits

  • prickly pear

  • cane toads

• urbanisation

  • clearing of native vegetation – removal of forests 

  • increased run-off

  • altering of waterways

  • destruction of native habitats – creation of ecological islands

  • waste disposal

• agriculture

  • clearing native vegetation

  • effects on climate of the removal of forests

  • effects of removal of mangroves on coastal marine communities

  • erosion & loss of topsoil

  • use of fertilisers

  • use of pesticides, herbicides and defoliants

  • destruction of native habitats

  • creation of ecological islands

  • removal of native species - kangaroos, wallabies, crocodiles

  • introduced species – hard hoofed animals

  • effects of planting monocultures on pest distribution and abundance

  • reduction in species diversity

  • effects of agriculture (incl. road building) on coastal coral reef communities

• pollution

  • water

  • air

  • land

Biological Control

• biological control involves the use of one organism to control the abundance and distribution of another

• used as an alternative to chemical control – pesticides 

Current Issues

• Global Warming

• Conservation