BIOLOGY 290 Lecture Notes - Lecture 2: Demographic Transition, Industrial Revolution, Gapminder Foundation

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1 Sep 2016
Biology 209D 9/1/16: Human Population Growth
- Human population from 10,000 BC has been slowly and steadily increasing until the industrial
revolution when population skyrocketed
- If birth rate exceeded death but both are constant, how would the pop. Grow?
oPrediction: linear
Modeling Human Population Growth
- Nt = population size census t
- D = fraction of individuals dying before the next census
- B = number of new born individuals per capita that survive to the next census
- Nt+1= (1-D)Nt + BNt = (B-D+1)Nt
o1-D=fraction surviving since the past census, multiplying by Nt gives number of
surviving people
oB is per-capita birth, so multiplied by Nt gives number of new individuals
oLambda = (B-D+1)
If B>D, lambda is >1 then population is growing
B=D, lambda=1, population is static
B<D, lambda<1, population is shrinking
oBased on this formula, constant values for B and D would yield geometric growth
oFormula is recursive, take one years population and get the next years population; need
an equation to give the population many years into the future
- N1=lamdaN0
- N2=lambdaN1=lambda(lamdaN0)
- Nt=lambdatN0
- Log Nt = log lambda^t + log No
- Log Nt = t log lambda + log No
oOn a logarithmic scale, this would be a linear graph
Actual World Population Growth
- When we look at the actual data for human population growth, it is not geometric growth;
therefore birth and/or death rate has not been constant in the past ~600 year
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