Unit 3-Populations Notes

AP Environmental Science

Population characteristics

• Population size = the number of individual organisms present at a given time
• Population density = the number of individuals within a population per unit area
• High densities-easier to find mates, but increase competition, and vulnerability to predation
• Low densities make it harder to find mates, but individuals enjoy plentiful resources and space
• Population distribution (dispersion) = spatial arrangement of organisms within an area

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Population characteristics

• Sex ratio = proportion of males to females
• In monogamous species, a 50/50 sex ratio maximizes population growth
• Age Structure = the relative numbers of organisms of each age within a population
• Age structure diagrams (pyramids) = show the age structure of populations

Birth and death rates

• Survivorship curves = the likelihood of death varies with age and is plotted logarithmically.
• Type I: More deaths at older ages. Ex-Humans, elephants, whales
• Type II: Equal number of deaths at all ages. Ex-birds, fish, jellyfish, rodents, prey animals
• Type III: More deaths at young ages. Ex-frogs, oysters, redwoods, snapping turtles,

Four factors in changing population size

• Natality (birth rate) = births within the population
• Mortality (death rate) = deaths within the population
• Immigration = arrival of individuals from outside the population
• Emigration = departure of individuals from the population
• Natural rate of change=birth rate-death rate
• Growth rate formula =
• (Crude birth rate + immigration rate) - (Crude death rate + emigration rate) = Growth rate
• (18/1000+5/1000)-(10/1000+7/1000)=6/1000*100%=.6%

Exponential population growth

• Steady growth rates (%) cause exponential population growth
• Increases by a fixed percent
• Graphed as a J-shaped curve
• Ex-invasive species
• Exponential growth cannot be sustained indefinitely
• Occurs in nature with a small population and ideal conditions for a short time

Carrying capacity

• Carrying capacity (K)= the maximum population size of a species that its environment can sustain
• An S-shaped logistic growth curve
• Limiting factors slow and stop exponential growth
• Carrying capacity changes with environmental change
• Humans have raised their carrying capacity by decreasing the carrying capacity for other species
• Video

Population density affects limiting factors

• Density-dependent factors = limiting factors whose influence is affected by population density
• Predation, competition, disease, nutrients, food
• Density-independent factors = limiting factors whose influence is not affected by population density
• Natural disasters

a-Logistic growth

b and c-Boom and bust cycles

d-exponential growth followed by population collapse

Biotic potential and reproductive strategies vary

• Biotic potential = the ability of an organism to produce offspring
• K-selected species = animals with long gestation periods and few offspring
• Have a low biotic potential, stabilize at or near carrying capacity, good competitors
• Ex-Large animals, humans, elephants, whales,
• r-selected species = animals which reproduce quickly
• Have a high biotic potential, little parental care
• Ex-Plants, Sequoia, fish, frogs, insects

Population Graphs

Slope of line describes population

• upward slope-growth
• downward slope-decline
• steep slope-high rate of change
• gradual slope-low rate of change
• flat slope-no rate of change
• steepening slope-increased rate of change
• gradualizing slope-decreased rate of change

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Graph 1-refers to points on line

• A-exponential population growth
• B-population growing at a decreasing rate
• C-zero population growth
• D-population decreasing at greatest rate
• E-population decreasing at a decreasing rate

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Graph 2-refers to lines

• A-biotic potential (exponential)
• B-boom and bust cycles
• C-logistic growth
• D-linear (geometric) growth
• E-carrying capacity

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The human population is still growing rapidly

• Due to exponential growth, even if the growth rate remains steady, population will continue to grow
• Population over time map

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Demography

• Demography = the application of population ecology to the study of humans
• Demographers study population size,
• Density and distribution,
• Age structure, sex ratio,
• And birth, death, immigration, and emigration rates

Population distribution

• Increased density impacts the environment, but relieves pressure in less-populated areas
• Humans are unevenly distributed around the globe
• Highest population density is in temperate, subtropical, and tropical biomes
• Over 50% of population lives in urban areas.
• Asia is the most populated continent
• China is the most populated country
• Majority of population lives in developing countries and is of or younger than reproductive ages
• Video

Total Fertility Rate

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• Total fertility rate (TFR) = the average number of children born per female
• Increasing urbanization decreases TFR
• Children go to school, and increase costs
• With social security, elderly parents need fewer children to support them
• Women’s education is inversely correlated to TFR
• Replacement fertility = TFR that keeps the size of a population stable (2.1)

Population growth depends on various factors

• Whether a population grows, shrinks, or remains stable depends on:
• Rates of birth, death, and migration
• Birth and immigration add individuals
• 25 million environmental refugees/year
• Death and emigration remove individuals
• Technological advances led to dramatic decline in human death rates
• Widening the gap between birth rates and death rates resulting in population expansion

Doubling Times-Rule of 70

• Growth Rate-Percentage increase in population each year.
• To figure out the doubling time of a population, divide 70 by the growth rates
• doubling time=70/percentage growth rate
• How long will it take for Mali to double its population with a growth rate of 3%?
• 70/3=23.3 years

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Life expectancy is increasing

• Natural rate of population change = due to birth and death rates alone
• In countries with good sanitation, health care, and food, people live longer
• Life expectancy = average number of years that an individual is likely to continue to live
• Increased due to reduced rates of infant mortality
• Urbanization, industrialization, health care, and personal wealth

The demographic transition’s four stages

• Demographic transition = a model of economic and cultural change to explain the declining death and birth rates in industrializing nations.
• Preindustrial: Most of human history before industrial revolution. High birth rates-infant mortality, family labor. High death rates-disease, unreliable food and water, poor medical care. Stable population.
• Transitional: High birth rates-habit. Lowering death rates-increased food production and better medical care. Massive population growth.
• Industrial: Lowering birth rates-women's education and opporunity, children less valuable, birth control. Slowing population growth.
• Post-industrial: Stable population, possibly shrinking, enjoys fruits of industrialization.
• Animation

Age structure affects future population size

• Size of population by male and female, pre-reproductive ages, reproductive ages, and post reproductive ages.
• Shapes tell us about future changes
• Rapid population growth-upward curving from base to tip with increasing slope. Developing countries-Madagascar, Guatemala, Nigeria
• Slow population growth-straight angled line from base to tip. Developed countries-US, Australia
• Stable population-Developed countries-vertical pyramid, rounded at the top.Ex-Spain, Portugal, Austria
• Declining-Pyramid top is wider than base. Developed countries-Russia, Italy, Japan. Senior care? Animation

Empowering women reduces growth rates

• Fertility rates drop when women gain access to contraceptives, family planning programs and better educational opportunities
• 2/3 of people who cannot read, and 60% of those living in poverty are women
• Kerala India Animation
• In 2007, 54% of married women worldwide used contraception;
• China = 86%; the U.S. = 68%; 20 African nations < 10%
• Women with little power have more unintended pregnancies
• Iran, Bangladesh, Kenya, and the Dominican Republic have invested more in family planning, education, health care, and reproductive rights than their neighbors.

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Population Policies and Family Planning Reduce Growth Rates

• Funding and policies that encourage family planning lower population growth rates in all nations
• Thailand-family planning education, growth rate to fall from 2.3% to 0.7%
• Bangladesh-outreach program on contraception, fertility rates fell from 7 to 3.2.
• International Conference on Population and Development 1994-179 nations called on all governments to offer universal access to reproductive health care within 20 years
• Income also reduces growth rate
• The US dropped funding for UNFPA during the Bush administration and restored it during the Obama administration

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Case study: China’s one-child policy

• In 1970, China’s 790 million people faced starvation
• The government instituted a one-child policy
• China’s growth rate plummeted
• In 1984, the policy exempted ethnic minorities and farmers
• Unintended consequences: killing female infants, black-market trade in teenage girls

Is population growth really a problem?

• Population growth results from technology, sanitation, food
• Death rates drop, but not birth rates
• Some people say growth is no problem
• New resources will replace depleted ones
• But, some resources (i.e., biodiversity) are irreplaceable
• Quality of life will suffer with unchecked growth
• Less food, space, wealth per person

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Causes and consequences of population growth

Population growth affects the environment

• The IPAT model: I = P x A x T x S
• Our total impact (I) on the environment results from the interaction of population (P), affluence (A) and technology (T), with an added sensitivity (S) factor
• Population = individuals need space and resources
• Affluence = greater per capita resource use
• Technology = increased exploitation of resources
• Sensitivity = how sensitive an area is to human pressure
• Further model refinements include education, laws, ethics
• Humanity uses 1/3 of all the Earth’s net primary production

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Computer simulations predict the future

• Simulations project trends in population, food, pollution, and resource availability
• If the world does not change, population and production will suddenly decrease
• In a sustainable world, population levels off, production and resources stabilize, and pollution declines

Poverty increases degredation

• Africa’s Sahel region and western China is turning to desert as people overharvest firewood and overgraze
• How do we feed a growing population?
• Increase the genetic diversity of food crops
• Develop systems to make global food distribution more equitable
• Increase the area of land dedicated to crop production by reducing area dedicated to meat production
• Assist developing countries in using efficient crop irrigation systems and erosion prevention methods
• We cannot increase arable land dramatically because there is not much available and habitat loss would worsen.

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Wealth also produces severe environmental impacts

• The population problem does not exist only within poor countries
• Affluent societies have enormous resource consumption and waste production
• People use resources from other areas, as well as from their own
• Individuals’ ecological footprints are huge and they eat more meat
• One American has as much environmental impact as 6 Chinese or 12 Indians or Ethiopians
• The richest 20% use 86% of the world’s resources

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HIV/AIDS impacts African populations

• Of 40 million in the world infected, 27 million live in sub-Saharan Africa
• Low rates of contraceptive use spread the disease
• 1 in 5 people in southern African nations are infected
• 6,000 Africans die each day
• Increased infant mortality
• Life expectancy fell from 59 to 40
• Millions of orphans created
• Young, productive people die
• Communities break down
• Income and food production decline
• Medical expenses and debt skyrocket.
• AIDS undermines the transition of developing countries to modern technologies

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Summary

• The human population is larger than at any time in the past
• Populations are still rising, even with decreasing growth rates
• Most developed nations have passed through the demographic transition
• Expanding rights for women slows population growth
• Will the population stop rising through the demographic transition, restrictive governmental intervention, or disease and social conflict caused by overcrowding and competition?
• Sustainability requires a stabilized population in time to avoid destroying natural systems