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  • Created by: romy kale
  • Created on: 03-10-13 19:14

Sigmoid pop curve

Sigmoid population curve

  • Slow growth (Lag Phase)  BR and DR low bees need to build hive, fungi need to produce extracellular enzymes etc... 
  • Rapid growth (Log phase) BR high DR low- No factors limiting pop. growth, nutrients plentiful and waste products have not built up to harmful levels. 
  • Stable State, no growth (stationary phase) BR high DR high- Factors start to limit population growth and population reaches equilibrium. Food shortages, inreased likelihood of disease... 
  • Decline phase BR low DR high (numbers drop) Resources become too limited, build up of toxic waste
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Calculating population growth

  • balance between birth and death rate
  • (number of births+number of immigrants)-(number of deaths+number of emigrants)

Data Handling

BR is number of live births per year (per 1000 of population)=

DR is number off deaths per year (per 1000 of population)=

Rate of Population growth= BR-DR

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Factors affecting human population growth

Affects on Birth Rate:

  • Population structure e.g. low number of people of reproductive age within population= Low BR
  • Availability of contraception
  • Infant mortality rate- reflects standard of medical care during pregancy/labour etc. Countries with high IMR tend to have higher BR as people have more children as likely some will die
  • economic conditions- poorer countries= high BR as children can make money
  • Political pressure- China's One child policy= low BR
  • Religious beliefs- Catholics= no contraception= high BR

Affects on Death Rate

  • Food supply/ better nutrition
  • Water supply and sanitation
  • Life expectancy at birth- lower in poor countries
  • War/natural disasters
  • better healthcare
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