APES Unit 3

Baby boom

Significant increase in birth rates that occurred in the United States from approximately 1946 to 1964, following World War II

• create changes in population dynamics as they move through the age structure—-create competition for jobs, dominate demands for goods and services and have political control

• echo-boom generation 1977-2000 largest generation ever; It would cause a population decline as they die off

Carrying capacity (K)

The maximum number of individuals in a population that an ecosystem can support—based on limiting resources

• population can briefly “overshoot“ (K) and then die-off happens

• limiting resources like food, water, habitat, etc…

Crude birth rate

Number of births per 1,000 individuals per year

Crude death rate (CDR)

Number of deaths per 1,000 individuals per year

Demographic bottleneck

Specific demographic characteristics of a population become skewed or unbalanced, limiting the population’s ability to grow or sustain itself

• demographic characteristics such as age distribution, sex ratio, reproductive rate, etc…

• often result from selectives pressures, environmental changes, or human impacts

• can happen even if the overall population size remains stable—happens when the demographic structure becomes skewed

• ex. population of species where most individuals are too old to reproduce

• ex. population heavily affected by hunting or fishing that skews the ratio

Demographic transition

A model that describes the changes in birth and death rates a country experiences as it develops economically

Stage 1: Pre-Industrial (Demographic Transition Model)

• High birth and death rates

• Slow/stagnant population growth

• Caused by limited access to healthcare, high infant mortality, and subsistence farming

• Virtually no country is in stage 1

Stage 2: Transitional/Industrializing/Developing (Demographic Transition Model)

• High birth rates, declining death rates (from improvements in healthcare, sanitation, and nutrition)

• Rapid increase in population growth

• Caused by advances in medicine and hygiene (lower mortality rates)

• Economic/Societal factors:

  • low GDP per capita

  • shorter life expectancy

  • declining IMR

  • high TFR

  • low literacy rate/school life expectancy for girls

• ex. Africa, Guatemala, Afghanistan, etc…

Stage 3: Industrialized/Developed (Demographic Transition Model)

• Declining birth rates and low death rates

• Slower population growth

• Caused by urbanization, access to contraception, and changing social norms regarding family size

• Economic/Societal factors:

  • higher GDP per capita

  • long life expectancy

  • low IMR

  • TFR is near replacement level (~2.1)

  • high literacy rate/school life expectancy

• Ex. Mexico, Kenya, South Africa, etc…

Stage 4: Post-Industrial/Highly Developed (Demographic Transition Model)

• Low birth and death rates

• Stabilized or negative population growth

• Caused by high levels of education (particularly for women) and a focus on careers

• Economic/Societal factors:

  • very high GDP per capita

  • longest life expectancy

  • TFR is below replacement level (<2.1)

• ex. Canada, US, South Korea, etc…

Developed country

Countries that have a large stock of physical capital and in which most people have a high standard of living

• World Bank classification

Developing country

Countries with low or middle levels of GNP per capita

• World Bank classification

• GNP per capita is a measurement that reflects a country’s average productivity per person

Emigration

Species going out of an environment

Family planning

The effort to plan the number and spacing of one’s children, so as to offer children and parents the best quality of life possible

Gross domestic product (GDP)

The value of all final goods and services produced in a country in a given year

• one of the most common ways to measure a country’s economic health

• includes things such as investments, consumption, government spending, exports minus imports, etc…

Growth rate (r)

% increase in a population (usually by year)

Immigration

Species coming into an environment

Infant mortality rate

The number of deaths of infants under one year per 1,000 live births in a given year

• higher IMR → higher TFR due to families having replacement children

  • lower IMR → lower TFR

• higher in less developed countries due to lack of access to: health care, clean water, enough food

Intrinsic rate of increase

The maximum potential for reproduction and survival within a species under ideal conditions with unlimited resources

• # births -(minus) # deaths

Nonrenewable resource

Energy sources that cannot be replenished or regenerated within a human lifespan

• finite resources that will eventually run out if used at a faster rate than they can be naturally formed

Per capita

Per person

Population density

Population/Area

• a measure of the number of individuals living in a particular area, usually expressed as the number of people per square kilometer or square mile

Population overshoot

When a population briefly exceeds carrying capacity

• ex. deer breed in fall, give birth all at once in spring; sudden spike in population = overshoot

• r-selected species are more likely to grow at a rapid rate and overshoot

• K-selected species have better production regulation and are more likely to maintain population at carrying capacity

Replacement-level fertility

Total fertility rate (TFR) needed for a population to replace itself without any increase or decrease

• often slightly above 2 children per woman in developed countries

• often higher in less developed countries due to infant mortality

Rule of 70

A way to predict the doubling time of a population size

• dividing the number of 70 by the percentage population growth approximates the population doubling time (70/r)

Subsidies

In environmental science, financial support provided by governments to encourage certain economic activities or behaviors

• can include direct payments, tac breaks, grants, etc…

Sustainable yield

The amount of resource that can be harvested without decreasing the food supply

Total fertility rate (TFR)

The average number of children born per woman

• higher TFR = high birth rate → higher population growth rate

• affected by:

  • age of first pregnancy

  • educational opportunities

  • family planning

  • governmental policies

  • infant mortality rates

  • healthcare access

Survivorship curves (S curves)

Line that shows survival rate of a cohort (group of same-aged individuals) from a population from birth to death

• steep slope/faster drop in line = quicker die-off of individuals

• slower drop in line = longer average lifespan

Type I curve

• Early life - high survivorship because high parental care

• Mid life - high survivorship because large size and population

• Old age - rapid decrease in survivorship

  • most mammals (ex. humans)

  • mostly K-selected

  • late loss

Type II curve

• Steadily decreasing survivorship throughout life

  • in between r and K selected

  • constant loss

Type III curve

• Early life - high mortality (low survivorship) because little to no parental care

• Mid life - few make it; slow, steady decline in survivorship

• Old age - even fewer make it; slow decline in survivorship

  • ex. insects, fish, plants

  • mostly r-selected

  • early loss

Die-off/Die-back

Sharp decrease in population size when resource depletion (overshoot) leads to many new fawns feeding in spring

Predator vs. Prey relations and carrying capacity

• Prey population increase due to low predator population

• Predator population increase due to more food/prey

• Increasing predator population limits prey population; leading to die-off of prey populations

• Prey die-off decreases predator’s food source; leading to die-off of predator populations

• Prey population increase due to low predator population (repeat and continues to repeat)

Size (population characteristic)

Total number of individuals in a given area at a given time

• larger = safer from population decline

Density (population characteristic)

Number of individuals in an area

• ex. 12 panthers/km^2

• high density = higher competition, possibility for disease outbreak, possibility of depleting food

Distribution/Dispersion (population characteristic)

How individuals in a population are spread out compared to each other

• Random (ex. trees)

• Uniform (ex. territorial animals)

  • evenly-spaced distribution of individuals within a population

• Clumped (ex. herd/group animals)

Sex ratio (population characteristic)

Ratio of males to females

• closer to 50:50 is usually more ideal for breeding

• die-off or bottleneck effect can lead to skewed sex ratio (not enough females), limiting population growth

Density-dependent factors (growth factors)

Factors that influence population growth based on size

• ex. food, competition for habitat, predation, water, light, disease, etc…

  • all limit population growth based on their size

  • small population doesn’t experience them, large ones do

  • tend to be biotic

Density-independent factors (growth factors)

Factors that influence population growth independent of their size

• ex. natural disasters (floods, hurricanes, tornadoes, fires…), droughts

• doesn’t matter how big or small a population is, natural disasters affect both

• tend to be abiotic

Biotic potential graph

Max. potential growth rate, with no limiting resources

• may occur naturally, but limiting resources slow growth and eventually limit population to carrying capacity

• exponential growth/curve

• J-shaped

• all species experience this when they are small and first starting

Environmental resistance graph

Initial rapid growth, then limiting factors limit population to K

• logistic growth/curve

• environmental resistance → factors that limit growth

• S-shaped

Population growth rate equation

(immigrants + births) - (emigrations + deaths)

• if = (-), population is decreasing

• if = (+), population is increasing

• if = 0, population is stable

• add total to existing population when done (subtract technically if negative)

Fecundity

Ability to produce offspring

Why are human populations sort of different from natural populations? (population growth)

Humans can alter their resource availability and carrying capacity

Age cohort

Groups of similarly aged individuals

Pre-reproductive age cohort

0-14 years old

Reproductive age cohort

15-44 years old

Post-reproductive age cohort

45+ years old

Larger pre-reproductive cohort indicates:

Current or future growth

Roughly equal reproductive and pre-reproductive cohorts indicate:

Slight growth/stable

Reproductive cohort AND/OR post-reproductive cohort is larger:

Population decline

Extreme pyramid shape (age group cohort)

Rapid growth

• often less developed countries that want children in the workforce

• to remember: stairs are easy to climb, and you can rapidly increase on them

• ex. Guatemala, Nigeria, Saudi Arabia, etc…

Less extreme pyramid shape (age group cohort)

Slow, stable growth

• often less developed countries that want children in the workforce

• to remember: a bit hard to climb, so you increase more slowly

• ex. United States, Australia, Canada, etc…

House (age group cohort)

Stable, little to no growth

• more well-developed nations who have a focus on education

  • citizens will be focused on education, not necessarily children

• to remember: very hard to climb, stay stable at one/a couple stairs

  • ex. Spain, Portugal, Greece

Narrowest at base (age group cohort)

Declining population

• more well-developed nations who have a focus on education

  • citizens will be focused on education, not necessarily children

• to remember: practically impossible to climb stairs, so you decline (go down first stairs cause you realize you can’t climb it, so you climb down—kind of a stretch)

• ex. Germany, Bulgaria, Italy

Factors in IMR decline

• Access to clean water

• Access to healthcare

• Food supply

How does development/affluence impact TFR?

Wealthy nations generally have lower TFR

• more educational access for women

• more economical opportunity for women

• higher access to family planning educations and contraceptives

• later age of first pregnancy

• less need for child to provide income through agricultural labor

How does government policy play a role in TFR?

Through coercive or noncoercive policies

• forced or voluntary sterilization

• ta incentives to have fewer children

• microcredits or loans to women without children to start businesses

• ex. China’s 1 (now 2) child policy

Malthusian theory

Earth has a human carrying capacity

• likely based on food production

• human population growth is happening father than growth of food production

• humans will reach a k limited by food

Technological advancement

Humans can alter earth’s k with technology innovations

• ex. synthesize fixation of nitrogen in 1918 leads to synthetic fertilizer, dramatically increasing food supply

Global population growth rate equation

(CBR-CDR)/10

Factors that increase population growth

• Higher TFR → higher birth rate

• High infant mortality rate can drive up TFR (with replacement children)

• High immigration level

• Increased access to clean water and healthcare (decrease death rate)

Factors that decrease population growth

• High death rate

• High infant mortality

• Increased development (education and affluence)

• Increased education for women

• Delayed age of first child

• Postponement of marriage age

Standard of living

What the quality of life is like for people of a country based on GDP

Life expectancy

Average a person will live to in a given country

• key health indicator of standard of living

• increases with access to clean water, health care, stable food resource

What do high GDP and life expectancy generally indicate?

Development and low population growth

Industrialization

The process of economic and social transition from an agrarian (farming) economy to an industrial one (manufacturing based)

Pre-Industrialized/Less developed nations

A country that has not yet made the agrarian to industrial transition

• typically very poor (low GDP)

• typically very high death rate and high infant mortality

• high TFR for replacement children and agricultural labor

Industrializing/Developing nations

Part way through transitioning from agrarian economy to industrial economy

• decreasing death rate and IMR

• rising GDP

Industrialized/Developed nations

Completed transition from agrarian economy to industrial economy

• very low DR and IMR

• very high GDP

• low TFR

Boom and bust cycle

When a population repeatedly overshoots the carrying capacity of their habitat and then crashes catastrophically

Percent birth rate equation

(Births/population)x100

Percent death rate equation

(Deaths/population)x100

Percent change

((New value-old value)/old value)x100