Population Pyramids

They are a useful graphic, also called age-sex pyramids, representation that give us the information to analyze population distribution and population change

Population numbers are the x-axis and age groups are on the y-axis.

*As we can see it can also be focused on only one sector of the population.

It shows:

• How many individuals are alive in different age groups cohorts in a country or region for any given year.
• Show the male-female ratio

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Types of Pyramid Shapes.

Stage 1. Expanding – High CBR *(, rapid fall in each upward age group due to high CDR, short life expectancy.

Stage 2. Expanding – High CBR, fall in

CDR as more individuals live to the middle age, slightly life expectancy.

Stage 3. Stationary – declining CBR, low CDR, more individuals live to old age.

Stage 4. Contracting – low CBR, low CDR, higher dependency ratio (those that cannot work), longer life expectanxy

LEDC’s tend to be in stage 1 and 2, while MEDC’s are in the 3 and 4 stages.

Measures of Population Changes

Population change around time by the action of factors such as birth and death rate and migration.

The basic rate for measuring the fluctuations in population are the following:

Crude Birth Rate (CBR)

The number of births per 1000 individuals in a population per year.

Number of births x 1000

population size

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Crude Death Rate (CDR)

The number of deaths per 1000 individuals in a population per year.

Number of deaths x 1000

population size

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Natural Increase Rate

NIR = (CBR - CDR) / 10

Doesn’t consider immigration and emigration.

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Doubling time

The time in years it takes a population to double its size.

Doubling time = 70 / NIR

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Total Fertility Rate (TFR)

It is the average number of children 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

In developing countries, the fertility rate is usually higher than in MEDC’s

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Humans impact on the environment is not just given out by its growth, but also by resource use and pollution. It’s impact is affecter by:

• It’s affected by the amount of wealth
• Resource desire
• Resource need

Individuals in a population, specially in a human population, interact with the environment in different ways. We cannot generalize for all the organisms within a population.

Wait for a detailed list of identification of resource use and waste profiles in a further post.

Human Population Dynamics

A very interesting topic. How much does the human population can reach? Which is our carrying capacity?

Different opinions were shared in class. Some said that we had already past our carrying capacity for more than 4 billion organisms. Others said that we are reaching it already. The odd thing was that non of us though we have too much time before we reached our carrying capacity (K)

We have to take into account that in contrast to the other species, we have created a very complex economic system that maintains our society in order and measures the “power” of each entity. This directly affect the dynamics of the our population by stating the repartition of resources and define relationship between entities.

In order to establish an equal share of resources for each organism the population would have to decrease. This is because , even if the global economic system changes its standards, there isn’t enough resources to maintain the actual 6 billion human population.

A simulation of the human population dynamics can be found in this webpage www.breathingearth.net It’s pretty interesting.