ECOSYSTEMS

• HABITAT


  Where an organism lives
• population


  all the organisms of the same species in a habitat
• community


  populations of different species in a particular habitat
• ecosystem


  a community as well as all the non living things in an area
• abiotic feature


  non living
• example of abiotic factors

  temperature/ availability of water
• biotic factor


  living feature of eco system
• example of biotic factors

  • presence of predators/food
• niche


  role of a species within its habitat
• adaptation


  feature a member of a species has that increases their chance of survival
• every species has a unique niche
• if 2 species try to occupy the same niche then they will compete with each other until only one of the species is left
• physiological adaption


  process inside body
• behavioural adaption


  way an organism acts
• anatomical adaption


  structural features of organism bod
• population size


  total number of organisms of one species in a habitat
• carrying capacity


  maximum stable population size that an ecosystem can support
• INTERSPECIFIC COMPETITON


  organisms of different species compete against each other for the same resources
• INTRASPECIFIC COMPETITON


  organisms of the same species compete against each other
• • why is there variation in population sizes?
  • abiotic factors eg. conditions
  • biotic factors eg. competition
  • predation
• PRIMARY SUCCESSION


  Happens on newly formed/exposed land so no soil or material to start with eg. just bare rock.
• SECONDARY SUCCESSION


  Happens on land that has been cleared of all plants but where soil remains. eg deforestation by humans
• CLIMAX COMMUNITY


  final community with no further succession
• SUCCESSION


  Change in community over time due to change in environment/species presence
• Predation is one biotic factor that can cause the size of this population to change.

  Give one other biotic factor that can cause the size of a population to change.

  competition for resources
•    Suggest an explanation for the high proportion of endemic species on the Solomon Islands.

  •  isolation on islandsled to species adapted specifically to the conditions on the island via natural selection
  • interbreeding so can only live on the islands
• The correlation between vegetation cover and soil moisture content was tested statistically. These two factors were found to be positively correlated, and p < 0.05. Explain what this result means.

  increasing vegetation cover is related to increasing moisture content so can reject null hypothesis
• Explain one way in which colonisation by herbaceous plants could change the physical environment

  nitrogen fixation increased nitrate concentration 

  OR

  accumulation of dead decomposed matter leads to improved soil structure
• Describe how you would collect the necessary data to estimate the size of a population by the mark-release-recapture technique.

   capture, count and release - carefully mark to avoid detection then recapture, count marked and unmarked
• Explain how succession resulted in the formation of the forest.

  pioneer species colonise land and change environment by dying and decomposing

  This forms basic soil /humus and makes environment less hostile and changes abiotic conditions

  This means that new species can exist here

  as process repeats the soil becomes thicker and richer meaning more species can survive, such as trees

  the organisms which are best adapted to the changing ecosystem will out-compete and replace those which are less adapted.

  eventually a stable environment is formed and climax community is reached
• In areas of poor drainage the soil is waterlogged. In these areas the climax community is bog dominated by the moss, Sphagnum. Explain why bog is described as the climax community.

  stable community and no further succession will happen
•   Waterlogged soils lack oxygen. Suggest why trees are unable to survive in waterlogged soils.

  roots unable to respire (aerobically)so active transport of minerals / other metabolic effect stops;
• The water and soil in Sphagnum bogs are usually acidic. Suggest why Sphagnum is not fully decomposed after it dies.

  acidic conditions inhibit enzymes as H+ ions distort active site

  anaerobic conditions
• Explain how ploughing the mesquite pest into the soil makes it more fertile. it contains n fixing bacteria in roots

  controls pest size of the population without killing them all

  N fixing bacteria will release N into soil
• Several small rivers flow into this lake. These rivers flow through forested areas.Explain how deforestation might affect the process of succession in the lake.

  direct result of removing forest cover so increases chances of soil erosion / leaching

  effects on organisms in lakee.g. more sediment / nutrients
•  Succession occurs in natural ecosystems. Describe and explain how succession occurs.

  1. Colonisation by pioneer species

  2. Pioneers species change the environment e.g. forms soil/humus/organic matter/nutrients.

  3. Environment becomes less hostile for other/new species

  4. Previous species out-competed.

  4.   increase in biodiversity

  5.   climax community formed
•  Describe how you could estimate the size of a population of sundews in a small marsh.

  • divide area into sections using tape/transect
  • use quadrat
  • roll dice to generate coordinates
  • count number in each quadrant section
  • large sample and calculate mean per section
  •  mean number of plants per quadrat multiplied by number of quadrats to calc number of sundews
• Suggest and explain how digesting insects helps the sundew to grow in soil with very low concentrations of some nutrients.

  Digestion/breakdown of proteins;

    Provides amino acids
• 1. engue is a serious disease that is caused by a virus. The virus is carried from one person to another by a mosquito, Aedes aegypti. One method used to try to reduce transmission of this disease is the Sterile Insect Technique (SIT). This involves releasing large numbers of sterile (infertile) male aegypti into the habitat. These males have been made infertile by using radiation.

  (a)     Explain how using the SIT could reduce transmission of dengue.

  intraspecific competition to reduce population of mosquitos
• Explain the advantage of species occupying different niches.

  Less competition for food/resource