Population Dynamics

A simulation of the human population dynamics is in this webpage: www.breathingearth.net
It calculates 6,859,548,511 people at the time i entered.


Not only ours, but any population change over time due to many different factors that, in this course of ESS, are known as limiting factors:

• Density dependent factors: the impact these factors have depends on how many individuals are in the population. These are usually biotic factors.
• Density independent factors: those that affect a population regardless of its size. These are usually abiotic factors. 

(in this PDF of the Canadian Province Manitoba, are a list of many examples of limiting factors, and an interesting case)

Growth curvesA visual representation of the growth rate are the growth curves, that show a different type of population growth:  

• J-curve

It display an exponential growth that suddenly it will have what is known as a dieback, or a radical decrease, as a result of the fact the population have overpass the carrying capacity (K), which is the maximum amount of individuals an ecosystem can support without being affected. 

• S-curve

S-curves shown also a exponential growth, but in a middle point the rate of growth decrease as the population reaches its carrying capacity (K). This growth rate is consistent with density dependent factors. 


Measuring population changes: 


The main factors that affect the size of a population are: Birth rate, Death rate, Immigration and Emigration


The Crude Birth Rate (CBR) is the number of births per one thousand individuals in a population per year. It is calculating by dividing the number of births by the total population size and multiplying by 1000.

CBR=[(Number of Births)/(Population Size)]*1000
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The  Crude Death Rate (CDR) is the number of deaths per 1000 individuals. It is calculated the same as the CBR.

CDR=[(Number of Deaths)/(Population Size)]*100
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Doubling Time is the time in years it takes for a population to double its size.

Doubling Time= 70/NIR
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Natural Increase Rate is the rate of population that doesn’t consider immigration and emigration.

NIR = (CBR - CDR) / 10
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Total Fertility Rate (TFR)  is the average number of births that each woman has over her life time. It shows the potential of population change.

• A TFR > 2.0 results in a population increase
• A TFR < 2.0 results in a population decrease
• A TFR = 2.0 results in a stable population