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HBIO2 > Environment
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Development of settled communities

Early farming

  • Advantages
    • Humans settle down and can develop their culture (trading)
    • More food available
    • Humans can live in environments with low food supply
  • Slash and burn method
    • Burning trees leaves behind ash which is rich in nutrients
    • Yield falls with subsequent crops
    • Crops are harvested before they die/decompose
    • Nitrogen is not recycled and not returned to the soil
    • Soil becomes less fertile - farmers moved away after few years
  • Evidence for farmed animals
    • Age of death (predominantly adult sized bones )
      • Hunters kill animals of the extreme ages (very old and very young)
      • Those are more vulnerable and easier to hunt
    • Bone structure (different to wild animals due to selective breeding)
    • Pollen analysis (same type of pollen at farmed areas)


  • Effects
    • Felling one hectare will give space for agriculture for high income
    • But the land loses fertility after a few years
    • Using cleared land for cattle will give a low income per year
  • If the forest is kept
    • Medium income per hectare per year for fruit and rubber production
    • Income from tourists and medicinal plants
    • Gene pools of wild relatives of domesticated organisms - which may be used as a source of genes/alleles in selective breeding or genetic engineering
  • Tropical rainforests should be conserved to avoid [EXAM]
    • "Loss of species / decrease in diversity / loss of niches / disruption of food chains
    • Loss of pharmaceuticals / medicines / timber / wood
    • CO2 build-up in atmosphere / global warming
    • Leaching of ions / minerals / nutrients
    • Soil erosion / mud slides / flooding / desertification"2

Making other species work for us

Selective breeding

  • Cereals
    • Wild grasses loose seeds before they can be harvested
    • Stronger grasses retain seeds and can be sown the next year
    • Selectively taken grains from cereal grasses that produce a high yield
    • Other grains are eaten
    • Tall stalks allows hand picking
    • Strong stalks prevent lodging (wheat damaged by strong wind)
    • Short stalks
      • Prevent lodging
      • Better for harvesting by machinery
      • Energy from sunlight used to produce better grain rather than long stalk
  • Dogs
    • Barking dogs frightens predators (wild adult dogs don’t bark as much)
    • Wild dogs that attack children were killed
    • Selected to assist rounding up sheep and cattle
  • Cattle
    • Used because
      • Eat grass which cannot be used by humans
      • Stay in herds, easier to control
    • Dairy cattle - produce large volumes of milk
    • Beef cattle  - larger amount of muscle


  • Process in which different species make up a community over time
  • Autogenic succession: brought about by plants only
  • Allogenic succession: external factor (eg flooding) alters development of community
  • 1° succession / succession where no living organisms have been found before
  • 2° succession / community of living organisms have already been there / human activity damaged vegetation and stopped succession
  • CLIMAX COMMUNITY: final most complex stage of succession / affected by abiotic factors
    • Succession can stop before a tree community
    • Valley / top of a high mountain
    • Climate climax: climate affects succession and complexity
    • Grazing climax: grazing animals stop succession
    • Grazing sheep and cattle prevent grassland to revert to woodland
  • SERAL STAGES change the environment to decrease abiotic factors (whole succession = sere)
    • Different types of vegetation enter the area
    • Increases amount and depth of soil
    • Allows other plants to enter
    • Will create more niches / more complex food webs / higher diversity
    • More animals will enter the area
    • Species diversity and complexity of food webs increases until climax is reached