Human Population

Factors influencing Population size (pg 388) Density Dependant Factors = regulate populations according to the population density. 1) Predation = focuses most intensely on eggs and young, but also may be important for adults. Acts more strongly at high densities. 2) Competition = if resources are limiting, only a given number of individuals may persist in a given habitat (the number that can persist is the carrying capacity). 3) Parasites and Disease = have the greatest effect at high population densities. Can be important factors regulating population sizes in some cases. Since that are concentrated in relatively small areas. Density Independent Factors = factors acting randomly, with reference to the population density, to regulate population size. 1) Weather - unfavorable weather can limit breeding success or cause mortality during the non- breeding season (e.g., winter mortality). 2) Food Supply - abundance of food is often dependent on climatic factors, and in poor years food supply may limit population size.

Populations in transition (developed nations): I.High birth and death rate, little pop growth II.High birth rate but declining death rate, rapid growth III.Birth rate declines, pop growth declines Graphics from U. Maryland, Dept. Meteorology

POPULATION STRUCTURE The population pyramid displays the age and sex structure of a country or given area Population in Five Year Age bands Usually, but not always, In % to make for easier comparisons between countries OLD DEPENDANTS ECONOMICALLY ACTIVE YOUNG DEPENDANTS FEMALES To the right MALES To the left

Demographic transition- Pg 392

Population Pyramids related to the Demographic Transition Model Stage 1 Stage 2Stage 3Stage 4 Both birth rates and Death rates are High, so population growth rates are slow but population Is usually restored Due to high birth Rate. Short life Expectancy EXAMPLES Scotland before 1760 New Guinea Remote parts of Amazonia Population starts to grow at an exponential rate due to fall in Crude Death Rate. More living In middle age. Life expectancy rises Infant mortality rate falls. EXAMPLES Scotland Republic of Congo Population continues to grow but at slower rate. Low C Death Rate. Dramatically declining Crude Birth Rate. EXAMPLES Scotland Algeria, Tunisia Morocco IMPLICATIONS Low Crude Birth Rate and Crude Death Rate Higher dependancy ratio and longer life expectancy Crude Death Rate does Rise slightly because of The ageing population EXAMPLES Scotland today. Japan, USA There is some merit in including or considering a Stage 5 today with a declining population

Stage 5? It has recently been suggested that school age children today will be the first generation of modern Americans expected to have lower life expectancy than their parents The reason for this is increased childhood obesity and related diseases (diabetes, hypertension, etc…) More on related food and nutrition issues later

Population pyramid of a less developed nation Population Pyramid of Nigeria (1995)

World regions in the process of demographic transition birth rate death rate

Why is rapid population growth a problem? Basic population biology: More organisms mean fewer resources for each Dense population allows for higher disease and parasite transfer

Importance of Population Pyramids A BROAD BASE POPULATION PYRAMID MEANS: increase food production build more homes & schools plan for more job opportunities for the young in future implement birth control program/campaigns Usually agricultural with problems of overpopulation. Many Dependents

Population pyramid of a developed nation Population Pyramid of Sweden (1995)

Importance of Population Pyramids A NARROW BASED POPULATION PYRAMID MEANS: Birth rate and Death rate low Work out incentives to encourage more births Hiring foreign labor. Need workers to support the retired people and pay taxes for healthcare etc. Proper medical services & health care for the aged

Thailand Total Fertility Rate 2005 = 1.7 children per mother

Why is the Thai fertility rate declining? 2002 figure

Old-age security –agrarian: young support old –industrial: retirement plans; impersonal Child Mortality — Health Care –healthy kids = fewer kids –High infant mortality = More kids! Factors Influencing Family Size

Status of Women –education: provides alternative means of support –One of the best predictors of a population’s fertility rate is the educational levels of women in that population! Factors Influencing Family Size

What factors influence people to have more or fewer children? Weak correlation Factors that affect fertility more directly may include health care education for women, and availability of contraception

Fertility and Education

Family Planning –Availability of contraceptives –pre- & postnatal care for mother and child –spacing births: breastfeeding Factors Influencing Family Size Religious views on contraception and abortion ****** Many personal value judgments

Much stronger correlation (cause and effect?)

China’s one child policy China = 1/5 of world population, 1.3 billion Years ago, goal of one child per family set Incentives: paid for sterilization and abortions, one-child subsidy, job priority for only children, preferential medical care for only children- especially girls Penalties: aid received for first child must be returned when second born, taxation, no paid maternity leave for second child Fertility rate now ~1.7, but population still growing because of large # people in reproductive years

Factors Influencing Family Size Economics –agricultural: children work (asset) –industrial society: cost money to educate Education... is expensive –Agricultural society: not expected for “country kids” –industrial society: education mandated

Why is population growing rapidly in some places? (mostly developing countries) Is it a problem? What should be done?

Poverty, environmental degradation and high fertility rates are linked!

Billions of people Global “Carrying Capacity” Future???