APES Test 3 Populations Pt. 2 Midterm Review Flashcards
Density independent factors limiting populations
Population limiting factors taht operate independently of the population size
These factors will change the population’s size regardless of whether the population is large or small
Ex. fire, storms, earthquakes, and other catastrophic events
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How many people in the world?
Over 8 billion people in the world
Birth rate has actually fallen in the US and most developed countries worldwide
But that only means that in prosperous countries the population is increasing more slowly, and overall the world’s population is still increasing
World’s human population has increased since the 1950s, and it is predicted to increase, though less rapidly, into the 2060s
pre reproductive, reproductive, post reproductive
under 15, 15-45, over 45
Why do human populations change?
Populations can also change in number as a result of migration into and out of the population
Two important vocabulary words to describe human migration are emigration, which is the movement of people out of a population, and immigration, which is the movement of people into a population
In the Annual Growth Rate formula, immigration and emigration would also need to be expressed as rates per thousand in the population
Keep in mind that in general emigration and immigration are only small factors in the change in size of human populations; however, the US, unlike many other highly developed countries, has the third-largest population due to immigration
The most significant additions to human population are due to births: total fertility rate (TFR)
Total Fertility Rate (TFR)
Average number of children born per female in childbearing years (15-45)
Worldwide average 2.5
Developing Countries: Up to 6
Developed Countries: Replacement Fertility: ~2 (* replacement fertility rate may be higher than 2 if death rates are high)
This information is baesd on analysis of data from preceding years for the population in question
religion and culture are predictors of birth rates because in some countries, certain groups have a proclivity toward reproduction for religious reasons
Total fertility rates are predictions that provide a rough estimate, but they can’t be depended on because they assume that the conditions of the past will be the conditions of the future
If fertility rate is at replacement levels, a population is considered relatively stable
Why is replacement fertility 2.1 instead of 2?
Mortality
Compensates for deaths of children, existence of non-child bearing females, and other factors
Infant mortality rate
Number of deaths of children under 1 year old per 1,000 live births
Obviously whether mothers have access to good healthcare and nutrition has the greatest effect on the infant mortality rate
Other factors are sanitation, clean drinking water, environmental conditions, and political infrastructure
Changes in these factors can lead to changes in infant mortality rate over time
As we mentioned earlier, despite the relatively recent drop in total fertility rates worldwide, the world’s population is still increasing
This is because many members of the human population are future parents, so even if they only reproduce at replacement rate, there will be an overall increase in total population
Change in human population growth rate over time?
Human population has actually been growing exponentially for more than three centuries
Growth rate has declined
Female Empowerment and TFR
Strong association between education level of women and TFR
TFR < replacement level in most developed economies. Is this a cause for concern? Or a chance for environmental and natural resource relief?
If developed countries want to increase birth rates for economic reasons, they must balance the challenges of having children in an equitable way without harming social and economic mobility
Human Population Dynamics in modern times, reasons behind it
Birth and Death Rates alter human population dynamics
Population growth rates have declined worldwide, but especially in developed countries
Death rates have also dropped, as healthcare has improved
People are living longer lives, and there are far fewer infant deaths today than there were 100 years ago. This is due, in large part, to the Industrial Revolution, which improved the standard of living for millions living in industrialized nations
Other causes of the extension of the human life span are the developments of clean water sources and better sanitation, the creation of dependable food supplies, and better health care
Widening the gap between birth and death rates drives populations up
Other factors that limit human population growth
Availability of birth control and education for women limit the TFR
Negative density independent effects, such as major storms, fires, heat waves, or droughts can also be limiting factors
Also, density dependent effects of a population nearing carrying capacity, such as decreased access to clean water and air, lack of resources including food, disease outbreaks, and territory size can also limit growth, show that the carrying capacity of a given area, and of the Earth as a whole, are ultimate factors that will have to be reckoned with
Age-Structure Pyramids
Age structure pyramids are useful for graphically representing populations
Some age structure diagrams group humans into three categories by age; those who are pre-reproductive (0-14), those who are reproductive (15-44), and those who are post-reproductive (45 and older)
Each of these groups at the same stage of life is also called a cohort
Age pyramids, such as the one shown on the next page, group members of the population strictly by age, with each decade representing a different group
The x-axis contains the information relating to the percent or number of individuals in each of the age groups
We can use age structure pyramids to predict population trends; for example, when the majority of a population is in the post-reproductive category; the population size will decrease in the future because most of its members are incapable of reproducing
The opposite is true if the majority of a population is in the pre-reproductive category; these populations will increase in size as time goes on
Take a look at the shapes of the example age structure diagrams representing Niger and the US
As you can see, Niger has a large number of pre-reproductive and reproductive members in its population, while he US has a fairly even distribution
From this, we can see that the population of Niger should increase significantly over time – it has what is referred to as population momentum – while the population of the US should grow more slowly
Worries about populations, growing too big
1794, Thomas Malthus wrote An Essay on the Principle of Population
In it, he argued that populations have a propensity to increase, and that that tendency would only be curbed when the “means to subsistence” – the necessary resources to maintain a human population, such as food – grew to be in short supply
He argued that this was inevitable, since population multiplies geometrically while food production does so arithmetically
He predicted that when the lower classes of a society started to suffer hardship, famine, and disease, the increase of a population might be curbed
When good conditions returned, populations would naturally increase again
When the Green Revolution took place, rapid increase in global food supply was again followed by rapid population growth
At this point, many began to worry about human overpopulation – the idea that humans might overshoot the carrying capacity of the EArth as a whole and suffer some sort of catastrophe (usually called a Malthusian catastrophe)
When the began to look at the environmental impact of humans, not just on food supply but on the whole spectrum of ecosystem services, it became clear that the rate of population growth was not sustainable
Though some predictions of certain disaster did not come to pass since the Green Revolution and genetic modifications helped the food supply surpass predicted levels, the basic idea that continued population growth at the exponential rate that were being seen could not continue was sound
Population trends needed to change
However, a change began to take place as nations industrialized more and more
As nations began to become ”developed” – a term to describe countries with high economic indicators and standards of living – these countries saw a concurrent change in their population characteristics
Since countries seemed to follow a pattern of industrialization and development, and generally their population characteristics tended to follow a specific pattern as this happened, the idea was codified into the demographic transition model
Demographic transition Model
As societies advance, growth rate declines
Typically birth and death rates decline, stabilizing populations
Used to predict populations trends based on the birth and death rates of a population
In this model, a population can experience zero populations growth via two different means: as a result of high birth rates and high death rates; or as a result of low birth rates and low death rates
When a population moves from the first state to the second states, the process is called demographic transition
Four states
Pre Industrial state
Transitional state
Industrial state
Postindustrial state
Malthusian Theory
Think of this as carrying capacity concepts, but applied to human populations-
Populations grow and falla according to natural resources and conditions (eg. density dependent and independent factors), especially food supply
