BIOLOGY 290 Lecture Notes  Lecture 2: Demographic Transition, Industrial Revolution, Gapminder Foundation
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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= (1D)Nt + BNt = (BD+1)Nt
o1D=fraction surviving since the past census, multiplying by Nt gives number of
surviving people
oB is percapita birth, so multiplied by Nt gives number of new individuals
oLambda = (BD+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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