Population Size & Ecosystems

Population Size & Ecosystems

1. Population graphs

   • Oscillations
     • Predator-prey relationship causes both populations to oscillate
   • Sigmoid growth: usual pattern of growth= 1 step growth curve

2. Density-Dependent Factors

   • Environmental factors that have more effect if the populations in a given area is large
   • Disease, parasitism, predation, depletion of food supply
   • Biotic

3. Density-Independent Factors

   • Abiotic
   • Effect is the same regardless of population size
   • Temperature

4. Ecosystems: A characteristic community of interdependent species interacting with the abiotic components of their habitat

   • A sequence of energy changes

5. Abundance: The number of individuals in a species in a given area or volume

   • Capture-mark-recapture
   • Kicksampling
   • Quadrat
   • Kite diagrams

6. Distribution: The area/volume in which the organism of a species are found

   • Transect
     • Belt transect
     • Line transect

7. Food Chains

   • Energy leaves the system as heat
   • Length is dependent on
     • -The energy that enters the food chain at the 1st trophic level -Efficiency of energy transfer between trophic levels  -Predator and prey population -Size of the ecosystem: larger=longer
   • Photosynthetic efficiency: A measure of the ability of a plant to trap light energy
     • -Wrong wavelength of light -Light can be reflected -Light can be transmitted straight through the leag
   • Efficiency of energy transfer= Energy incorporated into biomass after transfer/ Energy available in biomass before transfer
   • There is a loss from the food chain at each level
     • -There is energy in molecules that are egested -Energy is lost as heat due to respiration - Energy remains in molecules in parts of animal that may not be eaten e.g. horns

8. Ecological Pyramids

   • Pyramid of Numbers
     • Does not take into account the size of the organisms
     • Area of the pyramid bar is proportional to the total number at each trophic level
   • Pyramid of Energy =feeding relationships
     • Area of bar decreases =energy loss from the ecosystem
     • Easy to compare the efficiency of energy transfer between trophic levels
   • Pyramid of Biomass
     • Inverted pyramid
     • Hard to measure accurately

9. Succession

   • Climax community equilibrium
     • GPP=Respiration
     • Constant quantity of humus
     • Complex food web
   • Bare rock ---> Deciduous forest
     • 1. Algae and lichen colonise the rock=pioneer community
       • 2. Formation of primitive soil
         • 3. As soil develops, herbaceous plants outcompete mosses. Seeds that can germinate in direct sunlight are favoured
           • 4.Tall grass starts to grow. Shade-tolerant species are established
             • 5. Soil thickens as plants and animals start to die
               • 6. Shrubs outcompete herbaceous plants
                 • 7. Soil deepens which increases the quantity of minerals and humus in the soil
                   • 8. Large trees outcompete shrubs
   • Secondary succession
     • Same sequence as primary succession but it's more rapid
   • Factors affecting succession
     • Human interference
       • Over-grazing
       • Farming of land
       • Deforestation
     • Migration
       • Arrival of spore, seeds and animals
     • Competition amongst organisms
       • Intraspecific-between individuals of the same species
       • Interspecific- between individuals of different species

10. Human Impact on the Carbon Cycle

    • Deforestation
    • Climate Change
      • Agriculture is vulnerable
    • Global Warming
      • Enhanced greenhouse gas effect

11. Human Impact on the Nitrogen Cycle

    • Fertiliser effects
      • Increase in nitrates
        • Decrease in species diversity
        • Harms all ecosystems
    • Eutrophication
      • Sewage and fertilisers leak into bodies of water

12. Carbon footprint

13. Nitrogen fixation

14. Nitrification

15. Ammonification

16. Denitrification

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