Ecosystems

• Ecosystem - All interacting living organisms and non-living factors within an area
• Habitat – the place where an organism lives.
• Population – all of the organisms of one species who live in the same place at the same time and can breed together.
• Niche – specific role of each species in an ecosystem.
• Community - all of the populations of different species living and interacting in a place at the same time
• Abiotic factors – non-living factors of an ecosystem
• Biotics factors – living organisms that affect an ecosystem
• Abiotic factors

  • temperature (enzymes/can cause migration)
  • light intensity
  • water availability
  • o2 availability (aerobic respiration),
  • soil factors (type, pH)
• Biotic factors

  • competition – interspecific and intraspecific
  • predation
  • disease
• Trophic levels – stages in the food chain

  Reflect levels of consumers in each level

  Input - light

  Outputs – heat energy, decomposers (waste materials)

  
• Biomass – mass of living material in an area / organism without H20
• How do you measure biomass /dry mass?

  • Collect sample
  • kill organism
  • oven at 80.c. (periodically check mass of sample
  • When mass stays same – all water has been removed and remainder is biomass
  • use calorimeter (measures amount of calories/energy within an organism)
• units for biomass

  Land animals biomass: gm-2

  Marine animals biomass: gm-3
• Efficiency of biomass transfer -

  (Biomass at higher trophic level / biomass at lower trophic level) x 100
• Ecological efficiency

  Efficiency in which biomass/ energy is transferred from one trophic level to the next
• Useful energy is used to build biomass.
• ecological efficiency is never 100%-             

  • sunlight reflected (only 10% is used in photosynthesis)
  • other factors affecting photosynthesis rate
  • Some energy used up for photosynthesis to occur.
  • Energy is used / converted to glucose when organisms respire which is converted to heat.
  • Energy lost through excretion.
  • Some parts of food not eaten/ broken down (fibres from vegetables not digested)
• Productivity – rate of production of new biomass by producers
• Improving primary productivity to increase ecological efficiency

  • Plant crops early providing longer growing season to harvest more light
  • Grow crops in greenhouses - provides warmer temperatures / increases rate of PS
  • Genetic engineering /selective breeding - drought/disease-resistance strains
  • Crop rotation –stops reduction in soil levels of inorganic materials
  • Use of fungicides / herbicides / pesticides as factors reduce biomass
• Improving secondary productivity to increase ecological efficiency

  • Keep animals indoors (stable temperatures)
  • Keep fences (decreases movement – conserves energy for increased muscle mass
  • Feed high energy content food
  • Selective breeding – produce animals with high yields.
  • Use of antibiotics – could contribute to antibiotic resistance.
  • Harvesting animals before adulthood – minimises loss of energy
• Leaching - Nitrates flow into rivers and streams

  Waterlogged soils will have water filling up its air spaces – hence very low oxygen levels (anaerobic)
• Harvesting crop plants stops death of plants:

  ammonification and nitrification stops

  no absorption into plants

  so nitrate fertilisers needed

  leading to eutrophication – increased nitrates / so growth of  microorganisms / reduction in o2
• Nitrates taken up by plants needed for development of amino acids / growth for metabolic processes.
• Chemical symbols in Nitrogen cycle

  NH3 = Ammonia

  NH4+ = Ammonium

  NO2 - = Nitrites

  NO3- = Nitrates
• Decomposers –

  feed on dead organic matter and convert to inorganic matter

  Saprophytic

  Secrete enzymes – external digestion and absorb digested matter by diffusion
• Detritivores –

  Decompose organic matter

  Internal digestion

  Increase SA to increase decomposition
• Carbon

  • released in excretion
  • feeding
  • Death/ Fossilisation/ decomposition
  • Combustion
  • Respiration/ photosynthesis
  • Terrestrial plants use gaseous co2
  • Carbon forms carbonic acid in water
  • Enters rivers and lakes from weathering of limestone and chalk in form of hydrogen carbonate.
• Succession – progressive change in a community of organisms over time
• Climax community – final stable community that exists after succession has occurred
• Pioneer species - species which begin the process of succession (colonising the area as first living things there.)
• Example of succession

  1. Pioneer community live on bare rock

  2. Erosion of rock / build-up of dead, organic material produce soil for larger plants to grow / stabilise which may succeed the previous species.

  3. Larger plants succeed these small plants until a climax community is reached – often woodland.
• Secondary succession – takes place on previously colonised but damaged habitat
• Deflected succession – when succession is stopped/ interfered with

  • by grazing or when the lawn is mowed/ agricultural activity – spraying herbicides
  • Cutting grass at golf club keeps area in one stage of succession preventing growth of a climax community
• Outline the process of primary succession

  • Pioneer community:
  • begins with bare rock
  • and arrival of community as seeds or spores
  • pioneer species have certain adaptations, e.g. nitrogen-fixation
  • including grasses
  • followed by growth of shrubs and trees / Climax community which succeed prior community
  • decomposition changes composition of soil
  • increased organic, nitrate or water content
• Why may an area be an example of deflected succession

  climax community is prevented from developing

  as a result may be left with a shrub
• Suggest why it was not appropriate to estimate the number of jaguars using the capture recapture technique

  Human sightings:

  misidentification

  seeing the same individual twice / exaggeration

  
  

  footprints:

  might disappear (before recording)
• Describe how the student would use a belt transect to investigate the distribution of the two buttercup species.

  • lay tape measure out from edge of pond
  • place quadrat beside tape measure
  • identify species of buttercup in quadrat
  • count number of plants of each species (in quadrat)
  • repeat for positions of quadrat along tape
• Denitrification - opposite of nitrification
• Why would an area be described as a climax community

  stable area that is not subjected to further succession
• Population density of jaguars in a rainforest estimated to be 5 individuals per 100 km2.

  In 2007 study:

  >100 camera traps were set up covering an area of 271 km2.

  >28 images of 9 different jaguars were recorded.

  How well do these results support a population estimate of 5 individuals per 100 km2?


  Yes:

  • appropriate calculation of observed population density
  • support as figure is close enough to estimate

  No:

  • low repeatability / reproducibility of results
  • some individuals may not be photographed
  • if many individuals not trapped, population could be higher than estimate