Population Growth “People are everywhere. Some people say there are to many of us, but no one wants to leave” - Charles Schulz

How Populations Change Population – a group of individuals of the same species living in a particular place at a given time Fertility – births Mortality - deaths Immigration – moving into an area Emigration – moving out of an area

How Populations Change Fertility and immigration cause a population to rise Mortality and emigration cause a population to fall # births + # immigrants > # deaths + emigrants Population increases # births + # immigrants < # deaths + emigrants Population decreases

How Populations Change Mortality –Life expectancy at birth Average # of years a group of people born in the same year can be expected to live –Rising in most places –Sub-Saharan Africa – average life expectancy at birth = less than 50 years »Why so low? –World average = 63.8 years

How Populations Change Migration –Does migration change the population –A social event – much less predictable than fertility/mortality –The number of people immigrating to the US was 3 time higher than those leaving any other country –Over 3 million people immigrated into the US in 2002

Rate of Growth Most species produce more offspring than can survive and reproduce Biotic potential – maximum growth rate –Rate at which a population would grow if every new individual survived to adulthood and reproduced to maximum capacity Each generation would grow exponentially –(J-shaped curve)

Rate of Growth # of Individuals Generations

Rate of Growth Human biotic potential = 6% per year –Double in size every 11 years Biotic potential of bacteria = 250% per hour –Doubles in less than an hour cam2.htm

Limits to Population Growth Habitat resources –Food, shelter, mineral nutrients, water, light –Growing populations consume these resources rapidly Some have the ability to limit the growth rate = limiting resources Competition increases  mortality increases  fertility decreases

Limits to Population Growth Population reaches size in which it can no longer grow –Carrying capacity Maximum number of individuals an environment can support for long period of time –Creates an s-shaped curve

Limits to Population Growth

Population Videos Intro: news/7-billion/ngm-7billion news/7-billion/ngm-7billion p9sZk (How pop changed and grew over time) p9sZk Last video of chapter, TED _global_population_growth?language=en _global_population_growth?language=en

Growing Human Population Demography is the study of the characteristics of populations, especially human populations. –Demographers study the historical size and makeup of the populations of countries to make comparisons and predictions.

Growing Human Population Developed vs. Developing Countries –Developed countries have higher average incomes, slower population growth, diverse industrial economies, and stronger social support systems. –Developing countries have lower average incomes, simple and agriculture-based economics, and rapid population growth.

Growing Human Population Age structure – the classification of members of a population into groups according to age –Countries that have high rates of growth usually have more young people than older people.

Population Pyramids

The Demographic Transition The demographic transition is the general pattern of demographic change from high birth and death rates to low birth and death rates –Observed in the history of more-developed countries –Economic and social progress affects population growth rates.

The Demographic Transition 4 stages 1.Preindustrial –Birth and mortality rates both high –Population is stable 2.Transitional –Population explosion –Hygiene, nutrition, and education improve which lowers the mortality rate –Fertility rate still high

The Demographic Transition 3.Industrial –Population growth slows because birth rate decreases. As the birth rate becomes close to the death rate, the population size stabilizes. 4.Postindustrial –Birth rate drops below replacement level, so the size of the population begins to decrease.

The Demographic Transition

Overpopulation

Industrial revolution –Brought better healthcare and improved availability of food More people  stress on the infrastructure –Basic facilities of a country or region More people  stress on natural resources –Used faster than nature can replace them

Overpopulation Signs of overpopulation –- suburban sprawl, polluted rivers, barren land, inadequate housing, and overcrowded schools. Wood as fuel

Overpopulation Unsafe water –The population of most cities double every 15 years Infrastructure can’t keep up  unsafe water  disease

Overpopulation Impacts on land –Leads to less arable land Land that can be used for farming –Competition for agriculture, homes, and natural areas Urbanization –Increased density of people living in an urban area  suburban sprawl

World Demography