Population Growth

Population growth can be defined in terms of birth rate, death, doubling time, migration, and fertility rate.

The total fertility rate (TFR) is the average number of children that each woman has over her lifetime. Calculating this helps show the potential for population change in a country.

TFR > 2.0 = population increase
TFR < 2.0 = population decrease
TFR = 2.0 = stable population

Factors that impact our environment apart from population size, is the amount and distribution of wealth as well as the resource desire and need.

Population Growth and Food Shortages

There are two opposing theories on this subject: one by Thomas Malthus, and the other by Ester Boserup. Malthus states that the population is increasing geometrically while the food supply increases aritmethically. This means that the population will surpass the amount of food available, causing excess individuals to die off.
Boserup on the other hand states that while the population keeps growing it will develop the technology needed to meed the food demand. While Malthus is too pessimistic, Boserup is too optimistic. I think we need to find a middle ground. Also, population keeps growing and each country's demands are different. Will the population grow so much that it will cause a dramatic dieback? Have we surpassed our carrying capacity?

Human Development Index

The Human Development Index is a measure adopted by the United Nations Development Program as a way of calculating a country's well-being. It combines measurements of life expectancy, standards of living, education and GDP into one single value, which can be used to rank countries.

Taking this into consideration, two broad classifications can be used into which countries can be placed:

• MEDCs: Most economically developed countries
  
• LEDCs: Least economically developed countries

MEDCs are industrialized countries that have high GDPs. Their population is relatively rich and has a relatively low growth rate. These countries also have a high level of resource use.

On the other hand, LEDCs are less or not at all industrialized. These countries may have high natural capital, but it is usually exported to MEDCs where it is processed. LEDCs have lower GDPs and have higher poverty rates. Their population is large and has poor standards of living along with a high population growth rate.

Limiting Factors and Population Growth

Populations can change over time due to many different variables, known as limiting factors. These keep populations in check and can be classified into

• Density dependent factors
• Density independent factors

Density dependent factors are those that, as its name implies, depend on population density. This means that the impact these factors have depends on how many individuals there are. These are usually biotic factors, such as biomass, predation, competition.

Density independent factors are those that affect a population regardless of its size. These are usually abiotic factors. Some examples are pH, temperature, salinity, and also natural disasters such as tornadoes, earthquakes, volcanic explosions.

GROWTH CURVES

Growth rate can be graphed. There are two different types of curves:

• J-curve
• S-curve

Each shows a different type of population growth.

J-curves show exponential growth. The population grows exponentially and then crashes or suffers what is known as a dieback. This is because the population overshoots and exceeds the carrying capacity (K), which is the maximum amount of individuals an ecosystem can support without being affected. This is known as a boom and bust pattern. This growth rate is common in organisms.

S-curves start out as exponential growth, but then stabilize as the population reaches its carrying capacity. This growth rate is consistent with density dependent factors. This is known as a logistic curve.

S- and J-curves are idealized. In nature, both types of limiting factors act on the same population and the result is a combination of both curves.

And what about humans?

Human population seems to be growing exponentially, but in my opinion, seeing the conditions our planet is in, it seems as if we have surpassed our carrying capacity. Is the human population heading for a dieback? How much longer before the population crashes?