Populations Key ConceptsPopulations Key Concepts

Factors affecting population size Factors affecting population size

Species reproductive patterns Species reproductive patterns

Species survivorship patterns Species survivorship patterns

Conservation biology and human impacts on ecosystems

Conservation biology and human impacts on ecosystems

Population Dynamics and Carrying CapacityPopulation Dynamics and Carrying Capacity

Population dynamics Population dynamics

Biotic potential (intrinsic rate of increase [r]) Biotic potential (intrinsic rate of increase [r])

Environmental resistance Environmental resistance

Carrying capacity Carrying capacity

Exponential and Logistic Growth Exponential and Logistic Growth

Population Density Population Density

The biotic potential rmax is the population's capacity for growth.The intrinsic rate of increase (r) is the rate of population growth with unlimited resources.

No population can grow indefinitely due to limited resources such as light, water, and nutrients andalso due to competitors and/or predators.

Reproductive StrategiesReproductive Strategies

Reproductive StrategiesReproductive Strategies

Population DynamicsPopulation Dynamics

Populations change in size, density, dispersion and age structure.

Population density —the number of individuals of a population that inhabit a certain unit of land or water area.

Population dispersion —refers to how individuals of a population are spaced within a region.

Age structure of a population is usually described as the pre-reproductive stage, the reproductive stage and the post-reproductive stage. A population with a large reproductive stage is likely to increase, while a population with a large post-reproductive stage is likely to decrease.

Population dispersionPopulation dispersion

uniform dispersion a type of population dispersion in which the members of the population are uniformly spaced throughout their geographic region.

random dispersion —a type of population dispersion in which the position of each individual is not determined or influenced by the other members of the population.

clumping dispersion the most common dispersion pattern for populations. In this type of dispersion, individuals "flock together.“

Population DynamicsPopulation Dynamics

Four variables influence/govern population size: (1) births, (2) deaths, (3) immigration, and (4) emigration.

1) Increase in population occurs by birth and immigration.

2) Decrease in population occurs by death and emigration.

Factors Affecting Population SizeFactors Affecting Population Size

Fig. 9-3 p. 166

Biotic Potential v. Environmental Resistance

Po

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Carrying capacity (K)

Environmentalresistance

Bioticpotential

Exponentialgrowth

Carrying capacity (K) is determined by biotic potential and environmental resistance.

This is the number of a species' individuals that can be sustained indefinitely in a specific space.

Four variables influence/govern population size: (1) births, (2) deaths, (3) immigration, and (4) emigration.

Increase in population occurs by birth and immigration.

Decrease in population occurs by death and emigration.

Biotic Potential v. Environmental Resistance (Logistic Population Growth)

Exponential and Logistic GrowthExponential and Logistic Growth

Density and Limiting FactorsDensity and Limiting Factors The density of a population may or may not affect how rapidly it can

grow.

1. Density-independent population controls affect a population's size regardless of its density. These are abiotic factors in the community.

2. Density-dependent factors or population controls have a greater affect on the population as its density increases. Infectious disease is an example of density-dependent population control.

Natural Population CurvesNatural Population Curves

Fig. 9-7 p. 168

The Role of Predation in Controlling Population SizeThe Role of Predation in Controlling Population Size

Predator-prey cycles (Boom and Bust) Predator-prey cycles (Boom and Bust) Top-down control Top-down control

Bottom-up control Bottom-up control

Fig. 9-8 p. 168

Reproductive Patterns and SurvivalReproductive Patterns and Survival

Asexual reproduction Asexual reproduction Sexual reproduction Sexual reproduction

r-selected species r-selected species K-selected species K-selected species

Fig. 9-10 p. 170

Reproductive Patterns and SurvivalReproductive Patterns and Survival

Reproductive patterns can be classified into two fundamental reproductive patterns: r-selected and K-selected species.

r-Selected species are opportunists and reproduce when conditions are favorable or when disturbance opens a niche for invasion. Most species of this type go through irregular and unstable boom-and-bust cycles in population size.

K-selected species generally follow a logistic growth curve. Many of the larger species with long generation times and a low reproductive rate are prone to extinction.

Availability of a suitable habitat for individuals of a population ultimately determines the population size.

A survivorship curve is one way to represent age structure of a population.

Three generalized types of survivorship curves are: (1) late loss, (2) early loss, and (3) constant loss.

A life table shows the numbers of individuals at each age on a survivorship curve. Insurance companies use life tables to determine the cost of

insurance policies.

Populations of different species vary in how long individual members typically live.

Effects of Genetic Variations on Population SizeEffects of Genetic Variations on Population Size

Variations in genetic diversity can affect the survival of small, isolated populations.

Several factors can play a role in loss of genetic diversity and survival of a small population.

Founder effect is when a few individuals move to a new location that is isolated from the original population. There is limited genetic diversity in such a population.

Demographic bottleneck occurs when only a few individuals survive a catastrophe.

Genetic drift is a third factor and involves random changes in gene frequencies in a population. This may help or hurt the survival of the population.

Inbreeding occurs when members of a small population mate one another; this may increase the numbers of defective genes in a population.

Human Impacts on EcosystemsHuman Impacts on Ecosystems

Habitat degradation and fragmentation Habitat degradation and fragmentation

Ecosystem simplification Ecosystem simplification

Genetic resistance Genetic resistance

Predator elimination Predator elimination

Introduction of non-native species Introduction of non-native species

Overharvesting renewable resources Overharvesting renewable resources

Interference with ecological systems Interference with ecological systems

Human Populations Key ConceptsHuman Populations Key Concepts

Factors affecting human population size Factors affecting human population size

Managing population growth Managing population growth

Human population problems Human population problems

Factors Affecting Human Population SizeFactors Affecting Human Population Size

Population change equationPopulation change equation

Crude birth rate (BR) The crude birth rate is the number of live births per 1,000 people in a population in a specific year.|

Crude birth rate (BR) The crude birth rate is the number of live births per 1,000 people in a population in a specific year.|

Crude death rate (DR) The crude death rate is the number of deaths per 1,000 people in a population in a specific year

Crude death rate (DR) The crude death rate is the number of deaths per 1,000 people in a population in a specific year

PopulationChange

PopulationChange == (Births + Immigration) – (Deaths + Emigration)(Births + Immigration) – (Deaths + Emigration)

Demography is the study of the size, composition, and distribution of human populations and the causes and consequences of changes in these characteristics.

Describing Population ChangesDescribing Population Changes

Doubling Times “Rule of 70”: Doubling time is one measure of population growth.

Fertility-is the number of births that occur to an individual woman in a population.

Replacement-level Fertility —the number of children a couple must have in order to replace themselves in a population.

Total Fertility Rate (TFR) —the number of children a woman will bear during her lifetime; this information is based on an analysis of data from preceding years in the population in question.

Factors Affecting Human Population SizeFactors Affecting Human Population Size

There are currently more births than deaths throughout the world.

1. The annual rate of natural population change (%) equals birth rate minus death rate divided by

1,000 persons multiplied by 100.

2. The rate of the world's population growth has decreased.

3. The annual population growth dropped by almost half between 1963 and 2004, from 2.2% to

1.2%. But during this same period, the population base doubled from 3.2 to 6.4 billion.

Factors Affecting Human Population SizeFactors Affecting Human Population Size

There is a big difference in the exponential population growth rates of developed and developing countries, with developed countries growing at 0.25% and developing countries growing at 1.46%— almost six times faster.

The six fastest growing countries in terms of population are: India, China, Pakistan, Nigeria,Bangladesh, and Indonesia.

The populations of China and India comprise 38% of the world's population. The next most populated country is the United Stated with 4.6% of the world's population.

Factors Affecting Birth Rates and Total Fertility RatesFactors Affecting Birth Rates and Total Fertility Rates

Children in Labor Force Cost of raising and educating children Availability of pension systems Urbanization Education and employment for women Infant mortality rate Average marrying age Abortion Availability of birth control

Children in Labor Force Cost of raising and educating children Availability of pension systems Urbanization Education and employment for women Infant mortality rate Average marrying age Abortion Availability of birth control

Factors Affecting Birth Rates and Total Fertility RatesFactors Affecting Birth Rates and Total Fertility Rates

Many factors influence birth and fertility rates.1. More children work in developing countries; they are important to the

labor force.2. The economic cost of raising and educating children determines their

numbers. the more children cost, the less children people tend to have.3. If there are available private/public pension systems, adults have fewer

children because they don't need children to take care of them in old age.

4. People in urban areas usually have better access to family planning, so they have fewer children.

5. If women have educational and economic choices, they tend to have fewer children.

6. When the infant mortality rate is low, people have fewer children because children are not being lost to death.

7. The older the age at which women marry, the fewer children they bear.8. If abortions are available and legal, women have fewer children.9. The availability of reliable birth control allows women to space children

and determine the number of children they bear.

Who is Over Populated?Who is Over Populated?CNN-The People Bomb

Ages 0-14Ages 0-14 Ages 15-44Ages 15-44 Ages 45-85+Ages 45-85+

Rapid GrowthGuatemala

NigeriaSaudi Arabia

Rapid GrowthGuatemala

NigeriaSaudi Arabia

Slow GrowthUnited States

AustraliaCanada

Slow GrowthUnited States

AustraliaCanada

MaleMale FemaleFemale

Zero GrowthSpainAustriaGreece

Zero GrowthSpainAustriaGreece

Negative GrowthGermanyBulgariaSweden

Negative GrowthGermanyBulgariaSweden

Population Age StructurePopulation Age Structure

Fig. 10-14 p. 184Fig. 10-14 p. 184

The Demographic TransitionThe Demographic Transition

LowLow

HighHigh

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Stage 1Preindustrial

Stage 1Preindustrial

Stage 2Transindustrial

Stage 2Transindustrial

Stage 3IndustrialStage 3

IndustrialStage 4

PostindustrialStage 4

Postindustrial

Lowgrowth rate

Lowgrowth rate

Increasing Growthgrowth rate

Increasing Growthgrowth rate

Very highgrowth rateVery high

growth rateDecreasinggrowth rateDecreasinggrowth rate

Lowgrowth rate

Lowgrowth rate

Zerogrowth rate

Zerogrowth rate

Negativegrowth rate

Negativegrowth rate

Birth rate

Total population

Death rate

TimeTime

Fig. 10-20 p. 189

Solutions: Influencing Population SizeSolutions: Influencing Population Size

Migration Migration

Environmental refugees Environmental refugees

Reducing births Reducing births

Family planning Family planning

Empowerment of women Empowerment of women

Economic rewards and penalties Economic rewards and penalties