We have changed and are changing our environment

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)

Deforestation

• 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

Succession

• 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