Mader: Biology 8th Ed.

Ecology of Populations

Chapter 46

Mader: Biology 8th Ed.

Outline

• Scope of Ecology• Population Density and Distribution• Population Growth Models• Survivorship Curves• Age Distributions• Regulation of Population Size• Life History Patterns• Human Population Growth

– Environmental Impact

Mader: Biology 8th Ed.

Scope of Ecology

• Ecology - Study of the interactions of organisms with other organisms and the physical environment.– Habitat - Place where an organism lives.– Population - All the organisms within an

area belonging to the same species.– Community - All various populations

interacting at same locale.– Ecosystem - Community of populations.

Mader: Biology 8th Ed.

Ecological Levels

Mader: Biology 8th Ed.

Density and Distribution of Populations

• Population Density - Number of individuals per unit area or volume.

• Population Distribution - Pattern of dispersal of individuals within the area of interest.– Ecologists want to analyze and discover

what causes the spatial and temporal “patchiness” of organisms.

Limiting Factors are factors that particularly determine whether an organism lives in an area.

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Uniform Distribution

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Random Distribution

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Clumped Distribution

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Characteristics of Populations

• Intrinsic Rate of Natural Increase (r)– If immigration (+) and emigration (-)

cancel each other out, then population growth can simply be modeled by birth rate minus the death rate.

Mader: Biology 8th Ed.

Population Growth Models

• Exponential Growth– Number of individuals added each

generation increases as the total number of females increases.

Biotic Potential - Maximum population growth that can possibly occur under ideal circumstances.

Environmental Resistance - All environmental conditions that prevent populations from achieving biotic potential.

Mader: Biology 8th Ed.

Exponential Growth Curve

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Exponential Growth Equation

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Logistic Growth

• Logistic growth occurs when environmental resistance comes into play and retards exponential growth.– Living populations must eventually come

under the control of environmental resistance.

Mader: Biology 8th Ed.

Logistic Growth

Mader: Biology 8th Ed.

Logistic Growth

Mader: Biology 8th Ed.

Carrying Capacity

• Carrying Capacity is the maximum number of individuals of a given species the environment can support.– The closer the population to the carrying

capacity, the greater the environmental resistance.

Biotic potential is having full effect and birthrate is a maximum during exponential growth.

Mader: Biology 8th Ed.

Mortality Patterns

• A cohort is composed of all the members of a population born at the same time.– Survivorship is the probability of newborn

individuals of a cohort surviving to particular ages.

Survivorship Curves

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Survivorship Curves

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Survivorship Curves

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Age Distributions

• Populations differ according to what proportion of the population falls in each age category.– At least three structures possible.

IncreasingStableDecreasing

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U.S. Age Distributions

Mader: Biology 8th Ed.

Regulation of Population Size

• Density - Dependent Factors– Number of organisms present influences

the effect of the factor.CompetitionPredation

• Density - Independent Factors– Number of organisms present does not

influence the effect of the factor.Natural Disasters

Mader: Biology 8th Ed.

Life History Patterns

• r - Strategists (Opportunistic)– Produce large numbers of offspring.– Small body size.– Early maturity– No parental care.– Density independent controls.– Good dispersers and colonizers.

Mader: Biology 8th Ed.

Life History Patterns

• k - Strategists (Equilibrium)– Produce small numbers of offspring.– Large body size.– Late maturity– Significant parental care.– Density dependent controls.– Specialists

Mader: Biology 8th Ed.

Human Population Growth

• Human population has an exponential growth pattern.– Doubling time currently estimated at 53

years.• Population Size

– 1800 1 Billion– 1930 2 Billion– 1960 3 Billion– 2000 6 Billion

Mader: Biology 8th Ed.

World Population Growth

Mader: Biology 8th Ed.

Country Development

• More-Developed Countries (MDCs)– Slow population growth.– High standard of living.– Completed Demographic Transition.

North America and Europe• Less-Developed Countries (LDCs)

– Rapid population growth.– Low standard of living.

Latin AmericaAfrica and Asia

Mader: Biology 8th Ed.

Age Distributions

• Age Structure Diagrams divide populations into three age groups.– Pre-Reproductive– Reproductive– Post-Reproductive

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More-Developed Countries

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Less-Developed Countries

Mader: Biology 8th Ed.

Environmental Impact

• Environmental impact of a population is measured in terms of:– Population Size– Resource Consumption Per Capita – Resultant Pollution

Mader: Biology 8th Ed.

Environmental Impact

Mader: Biology 8th Ed.

Review

• Scope of Ecology• Population Density and Distribution• Population Growth Models• Survivorship Curves• Age Distributions• Regulation of Population Size• Life History Patterns• Human Population Growth

– Environmental Impact

Mader: Biology 8th Ed.