10.1 nature of ecosystems

• ecosystem


  • all organisms living in a particular environment
  • including its abiotic and biotic conditions
• trophic levels


  used to describe organism's feeding relationship.

  consists of...

  • producers - (autotrophs)
  • primary consumers (heterotrophs)
  • secondary consumer
  • tertiary consumer
  • decomposer
• producers


  • also known as autotrophs
  • use photosynthesis or chemosynthesis to produce organic molecules from inorganic sources
• consumers


  • also known as heterotrophs
  • feed on other organisms
• how can ecosystem structure be represented?

  • pyramid of number (count)
  • pyramid of biomass (weight)
  • pyramid of energy
• pyramid of number


  • total number of organisms in each trophic level

  strengths

  • easy to measure

  weakness

  • not accurate
• pyramid of biomass


  • total weight of dry biomass in each trophic level

  strengths

  • more accurate

  weakness

  • dry mass has to be used
  • organisms must be killed
• factor affecting the shape of the biomass?


  • season when measurement taken

  e.g aquatic animals, growth is rapid in certain seasons
• pyramid of energy


  • amount of energy that would be released on complete combusion of all organisms

  strengths

  • most accurate

  weakness

  • hardest to measure
• how is matter lost in the food chain?

  • Carbon dioxide via respiration
  • waste via faeces and urine
  • uneaten parts e.g bone, teeth, shell, bark
• how is energy lost in the food chain?

  • chemical energy in uneaten parts
  • movement of consumers
  • heart energy loss
• how does transfer of biomass occur?

  • producer eaten by primary consumer
  • biomass transferred to primary consumer level
  • primary consumer eaten by secondary consumer
  • biomass transfered.... etc
• role of decomposers?


  • cycling mineral and organic ions in ecosystem
  • hydrolyse waste products into inorganic molecules
• when investigating ecosystems, ecologists measure

  • abundance
  • distribution of organism
• methods of measuring abundace of non moving organisms

  • individual counts
  • percentage cover - estimating area of cover
  • ACFOR scale - estimate of frequency of organism
• how and when do you use individual counts?

  • count number of organisms
  • for larger organisms which are easier to count
  • for small populations
• how and when do you use percentage cover?

  • estimate area that is covered by organism

  used when...

  • organism cant be counted individually
  • organism forms continuous cover mostly (lichen etc)
  • organism are small, with large population
• how do you use the ACFOR scale?

  • make a subjective judgment
  • on the frequency of the organism
  • (abundant, common, frequent, occasional, rare)
• what are the 2 sampling methods? how do you ensure sample is representative?

  
  

  • using frame quadrats
  • using line transects

  representative sample ensured by...

  • randomisation method to get sample
  • device to determine size of sample
• how are quadrats used to get a random sample?

  • place grid over a map and get coordinates
  • replicate grid on sample area
  • generate random coordinates using generator
  • place quadrat at intersection of both coordinates
  • count the number of organisms
  • repeat 20x
  • calculate mean or percentage cover
• how are transects used to get a random sample

  used for abiotic factors which change across the area

  • lay 20m tape measure across area
  • belt transect - place quadrat continuously
  • line transect - place quadrat at regular intervals
  • measure number of organisms
  • calculate mean and percentage cover
• how do you assess the abundance for moving organisms?

  mark-release-recapture method

  • capture and count sample 1 (N1)
  • mark them without harming them
  • release them
  • give them time to disperse
  • capture sample 2 (N2)
  • count number of organisms from sample 1.
  • calculate population size
• how do you calculate population size?

  n1 x n2 / n
• what are the assumptions of assessing abundance of moving objects?

  • no births or deaths
  • no migration
  • behaviour of organism doesn't affect marking
  • representative samples taken
  • enough time for the sample to randomly mix
• why do we calculate spearman's rank correlation coefficient?

  • to measure the correlation between 2 variables
• how to calculate spearman's rank?

  1. rank data sets
  2. calculate the difference between ranks
  3. add the differences and square
  4. sub into the equation
  5. use critical value table to see if results are significant at p=0.05

  
• how are spearman's rank results interpreted?

  value close to +1 = positive correlation

  value close to -1 = negative correlation

  value of 0 = no correlation
• why do we calculate T test?

  • to see if the means and overlap between 2 sets of data are significantly different
• how do you calculate t test?

  1. calculate mean of both samples
  2. calculate standard deviation of both samples
  3. sub into equation
  4. determine degrees of freedom (sum of both samples - 2)
  5. check against critical value table at p=0.05

  
• how do you calculate standard deviation of a sample?


  ...