6.3.1 Ecosystems

What is an ecosystem

• Definition: A relatively self contained system including all the living organisms and the environment, interacting with each other

• Ecosystems are dynamic - as they change

• 3 types of change that affect population size

  • Cyclic changes

  • Directional changes

  • Unpredictable/ Erratic Changes

What are cyclic changes

The changes repeat themselves in a rhythm (e.g. predator-prey)

What are directional changes

Changes go in one direction. Certain variables continue to increase or decrease

What are Unpredictable/Erratic changes

No rhythm and no constant direction (e.g. hurricanes and wildfires)

What are Biotic factors

Factors that involve other living organisms e.g.

• Paratism

• Mutualism

What are abiotic factors

Factors that involve non-living components of the environment e.g.

• Edaphic Factors (factors relating to the soil)

• Atmospheric humidity

• Availability of inorganic ions

• Water supply

what is a tolerance curve

• A graphical representation to show how an organism’s survival, growth or reproductive success is affected by changes in specific environmental factors

• Some abiotic factors can be lethal at one extreme (e.g. toxicity and pollutants) which the graph will show

• On a tolerance curve, the organisms will survive, grow and reproduce in a much more broad range

What are the components of an ecosystem

• Habitats: the place where an organisms lives

• Population: all of the organisms of one species, who live in the same place at the same time and breed together

• Community: all the populations of different species, who live in the same place, at the same time, and who interact with each other

• Niche: the role of each species in an ecosystem

How is biomass transferred

How to calculate dry biomass

• Collect all the organisms and put them in an oven at 80 degrees celcius to evaporate all the water

• Check the mass periodically. Once the mass stops decreasing all the water had been removed. Record the mass once it stops changing

This method is destructive to the ecosystem, so ecology

How much biomass do organisms take in and why

• Organisms convert 10% of biomass in their food to their own organic matter because:

  • Not eating all of the biomass of an organism

  • Some energy being transferred to the environment (e.g. metabolic heat from respiration and movement)

  • Some parts of the organism are eaten but are indigestible

  • Some energy is lost in excretory materials e.g. urine

How do humans manipulate biomass transfers

• Agriculture manipulates the environment in order to increase the efficiency of the biomass transfers at each trophic level

• Plants and animals are provided with abiotic factors they need to survive

• Competition from other species is removed (e.g. weed killers)

• The threat of predators is removed (e.g. pesticides)

• Only very short food chains are created (two or three trophic levels)

How is primary productivity increased

• Manipulating light levels

• Irrigating. Roos and producing drought-resistant strains

• Manipulating temperature by growing plans in greenhouses

• Crop rotation increases nutrient levels

• Use of fertilisers

• Use of pesticides and producing pest-resistant strains

• Use of fungicides

How is secondary productivity increased

• Harvest animals just before adulthood

• Selective breeding

• Treating animals with antibiotics

• Restricting movement by supplying animals directly with food

• Control body temperature by keeping them indoors

How can succession be deflected

• Deflected succession: When succession is stopped or interfered with (by human activity)

  • E.g. farmers adding fertilisers and using herbicides

• Plagioclimax: The resultant sub climax community that results when an area is held in a particular stage of succession

• Deflected succession can make it hard to decide if an area warrants preservation or conservation