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4 Population EcologyPopulation EcologyC
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Lesson 4.1 Studying EcologyLesson 4.1 Studying Ecology
Ernst Haeckel defined ecology in 1866 as “the body of knowledge concerning the economy of nature—the total relations of the animal to both its inorganic and organic environment.”
Ernst Haeckel defined ecology in 1866 as “the body of knowledge concerning the economy of nature—the total relations of the animal to both its inorganic and organic environment.”
ObjectivesObjectives
•Describe the different levels of organization studied by ecologists• Explain the difference between biotic and abiotic
factors•Discuss how an organism’s habitat relates to its
survival
•Describe the different levels of organization studied by ecologists• Explain the difference between biotic and abiotic
factors•Discuss how an organism’s habitat relates to its
survival
Levels of Ecological OrganizationLevels of Ecological Organization
• Everything on Earth is connected, so how do ecologists study anything?
• Ecology is the study of how organisms interact with each other and with their environments
• Scientists study ecology at various levels of organization.
• Everything on Earth is connected, so how do ecologists study anything?
• Ecology is the study of how organisms interact with each other and with their environments
• Scientists study ecology at various levels of organization.
Lesson 4.1 Studying Ecology
Levels of Ecological OrganizationLevels of Ecological Organization
• Individual• Ecology involves describing relationships between individual
organisms and their environment.
• Populations• Individual organisms are classified into species
• Species is a group of individuals that interbreed and produce fertile offspring• Species have similar genetics
• Members of a species that live in the same area at the same time make up a population.• Ecology involves how individuals within a population interact
with one another.
• Individual• Ecology involves describing relationships between individual
organisms and their environment.
• Populations• Individual organisms are classified into species
• Species is a group of individuals that interbreed and produce fertile offspring• Species have similar genetics
• Members of a species that live in the same area at the same time make up a population.• Ecology involves how individuals within a population interact
with one another.
Levels of Ecological OrganizationLevels of Ecological Organization
•Communities• All of the populations in a particular area.• Ecology involves interactions among species.
• Ecosystems• Include all the livings things and their physical environments
within a particular area• Living and nonliving things.• Ecology involves studying the living and nonliving
components of a system together.
•Communities• All of the populations in a particular area.• Ecology involves interactions among species.
• Ecosystems• Include all the livings things and their physical environments
within a particular area• Living and nonliving things.• Ecology involves studying the living and nonliving
components of a system together.
Levels of Ecological OrganizationLevels of Ecological Organization
• Biosphere• Includes all parts of Earth that host life, with all of its
organisms and environments.• Ecology involves how matter and energy cycle through the
biosphere and influence organisms worldwide.
• Biosphere• Includes all parts of Earth that host life, with all of its
organisms and environments.• Ecology involves how matter and energy cycle through the
biosphere and influence organisms worldwide.
CheckpointCheckpoint
•What is the difference between a species and a population? Between a population and a community?•What is the difference between a species and a
population? Between a population and a community?
Biotic and Abiotic FactorsBiotic and Abiotic Factors• Biotic factors: Parts of an
ecosystem that are living or used to be living
• Ex: living tree, dead tree
• Abiotic factors: Parts of an ecosystem that have never been living
• Ex: oxygen, sunlight
Lesson 4.1 Studying Ecology
Did You Know? Decaying organisms are biotic factors as long as their structure remains cellular.
Did You Know? Decaying organisms are biotic factors as long as their structure remains cellular.
HabitatHabitat
• The specific environment in which an organism lives
•Habitats consist of biotic and abiotic elements.
•Habitats provide an organism with resources—anything an organism needs to survive and reproduce, including food, shelter, and mates.
• The difference between habitat and ecosystem is that a habitat’s boundaries are defined by the population that lives there.• Habitats may be a subset of an ecosystem OR habitats may be a
combination of ecosystems
• The specific environment in which an organism lives
•Habitats consist of biotic and abiotic elements.
•Habitats provide an organism with resources—anything an organism needs to survive and reproduce, including food, shelter, and mates.
• The difference between habitat and ecosystem is that a habitat’s boundaries are defined by the population that lives there.• Habitats may be a subset of an ecosystem OR habitats may be a
combination of ecosystems
Lesson 4.1 Studying Ecology
Objectives RevisitedObjectives Revisited
•Describe the different levels of organization studied by ecologists• Explain the difference between biotic and abiotic
factors•Discuss how an organism’s habitat relates to its
survival
•Describe the different levels of organization studied by ecologists• Explain the difference between biotic and abiotic
factors•Discuss how an organism’s habitat relates to its
survival
Lesson 4.2 Describing PopulationsLesson 4.2 Describing Populations
From 1900 to 2000, the white-tailed deer population of New York state grew from about 20,000 to more than 1 million. Densities of more than 100 deer per sq mi occur in some metropolitan areas.
From 1900 to 2000, the white-tailed deer population of New York state grew from about 20,000 to more than 1 million. Densities of more than 100 deer per sq mi occur in some metropolitan areas.
ObjectivesObjectives
• Explain the usefulness of tracking population size.•Define population density.•Describe the three ways populations can be
distributed.• Explain what age structure diagrams tell you about a
population.
• Explain the usefulness of tracking population size.•Define population density.•Describe the three ways populations can be
distributed.• Explain what age structure diagrams tell you about a
population.
Population SizePopulation Size
Lesson 4.2 Describing Populations
• The number of individuals in a population at a given time
• Sudden and dramatic decreases in population size can indicate an unhealthy population headed toward extinction.
• When population size increases or remains steady, it is often a sign of a healthy population.
Did You Know? The passenger pigeon was once North America’s most abundant bird. Hunting drove them to extinction in less than 100 years.
Did You Know? The passenger pigeon was once North America’s most abundant bird. Hunting drove them to extinction in less than 100 years.
Determining Population SizeDetermining Population Size
Counting Laysan Albatross Nests
• It is nearly impossible to count each individual in a population
• Population is estimated using sampling techniques.• Count individuals in
small sample area• Use that to estimate
number of individuals in large overall area
CheckpointCheckpoint
•When is sampling necessary?•When is sampling necessary?
Population DensityPopulation Density
Lesson 4.2 Describing Populations
• Measure of how crowded a population is
• Larger organisms generally have lower population densities.
• Low population density: More space, resources; finding mates can be difficult
• High population density: Finding mates is easier; tends to be more competition; more infectious disease; more vulnerability to predators
Northern pintail ducks
Population DistributionPopulation Distribution
Lesson 4.2 Describing Populations
• How organisms are arranged within an area:
• Random distribution: Organisms arranged in no particular pattern, resource are spread out
• Uniform distribution: Organisms evenly spaced; individuals hold territories/compete for space
• Clumped distribution: Organisms grouped near resources; most common distribution in nature
Population DistributionPopulation Distribution
CheckpointCheckpoint
•What is the difference between population density and distribution?•What is the difference between population density and
distribution?
Age StructureAge Structure
Lesson 4.2 Describing Populations
• Age structure describe the relative number of organisms of each age group within population
• Can be used to predict future population growth of a population
• Individuals capable of having offspring make up the reproductive group
• Young individuals who have not yet reached the age where they can reproduce are called pre-reproductive
• Older individuals past the age of having offspring are called post-reproductive
Age StructureAge Structure
• Population with even age distribution will likely remain stable (births = deaths).• Population made up of mostly post-reproductive
individuals will likely decline over time.• Population made up of mostly pre-reproductive
individuals will likely increase over time.
• Population with even age distribution will likely remain stable (births = deaths).• Population made up of mostly post-reproductive
individuals will likely decline over time.• Population made up of mostly pre-reproductive
individuals will likely increase over time.
Age Structure DiagramAge Structure DiagramA
ge
How will each population change over time?
Sex RatiosSex Ratios
Lesson 4.2 Describing Populations
• Proportion of males to females
• Age structure diagrams give information about sex ratios.
• For a monogamous species, the ideal sex ratio is 50:50.
Objectives RevisitedObjectives Revisited
• Explain the usefulness of tracking population size.•Define population density.•Describe the three ways populations can be
distributed.• Explain what age structure diagrams tell you about a
population.
• Explain the usefulness of tracking population size.•Define population density.•Describe the three ways populations can be
distributed.• Explain what age structure diagrams tell you about a
population.
Lesson 4.3 Population GrowthLesson 4.3 Population Growth
From 1800 to today, the human population has grown from about 1 billion to more than 6.8 billion—an exponential rate of increase.
From 1800 to today, the human population has grown from about 1 billion to more than 6.8 billion—an exponential rate of increase.
ObjectivesObjectives
•Describe the factors that influence a population’s growth rate.• Explain exponential growth and logistic growth.• Explain how limiting factors and biotic potential affect
population growth.
•Describe the factors that influence a population’s growth rate.• Explain exponential growth and logistic growth.• Explain how limiting factors and biotic potential affect
population growth.
Birth and Death RatesBirth and Death Rates
Lesson 4.3 Population Growth
• A population’s relative birth and death rates (natality and mortality) affect how it grows.
• When birthrate is greater than death rate, population size increases.
• When death rate is greater than birth rate, population size decreases.
• Survivorship curves show how the likelihood of death varies with age.
Birth and Death RatesBirth and Death Rates• Survivorship curves:
• Graphs that show how the likelihood of death varies with age• Type I curve has higher mortality at older ages• Type II curve has equal mortality rates at all ages• Type III curve has higher mortality rate at younger ages
• Survivorship curves:• Graphs that show how the likelihood of death varies with age• Type I curve has higher mortality at older ages• Type II curve has equal mortality rates at all ages• Type III curve has higher mortality rate at younger ages
CheckpointCheckpoint
•Which type of survivorship curve describes populations whose mortality is highest at young ages?•Which type of survivorship curve describes populations
whose mortality is highest at young ages?
Birth and Death RatesBirth and Death Rates
• Age Structure and Population Growth:• Consider a population following a type I survivorship curve
(higher mortality at older ages)• If population is made up of more young people, then there is
likely to be more births than deaths
• If population is made up of more old people, then there is likely to be more deaths than births.
• Age Structure and Population Growth:• Consider a population following a type I survivorship curve
(higher mortality at older ages)• If population is made up of more young people, then there is
likely to be more births than deaths
• If population is made up of more old people, then there is likely to be more deaths than births.
Immigration and EmigrationImmigration and Emigration
Lesson 4.3 Population Growth
• In addition to births and deaths, population growth is affected by immigration and emigration—individuals moving into and out of a population.
• Migration, seasonal movement into and out of an area, can temporarily affect population size.
Calculating Population GrowthCalculating Population Growth
Lesson 4.3 Population Growth
• Determined by the following equation: (birthrate + immigration rate) – (death rate + emigration rate)
• Growing populations have a positive growth rate; shrinking populations have a negative growth rate.
• Usually expressed in terms of individuals per 1000
Did You Know? Immigration contributes more than 1 million people to the U.S. population per year.
Did You Know? Immigration contributes more than 1 million people to the U.S. population per year.
Exponential GrowthExponential Growth
Lesson 4.3 Population Growth
• Population increases by a fixed percentage every year.
• Normally occurs only when small populations are introduced to an area with ideal environmental conditions
• Rarely lasts long
• Ex: Mold growing on bread
Logistic Growth and Limiting Factors
Logistic Growth and Limiting Factors
Lesson 4.3 Population Growth
• Growth almost always slows and stops due to limiting factors.
• Limiting factors: Environmental characteristics slow population growth and determine carrying capacity (largest population size a given environment can support).
• Density-dependent: Influence changes with population density; examples are competition for resources, predation, disease
• Density-independent: Influence does not change with population density; Examples are floods, fires, landslides
Logistic Growth and Carrying Capacity
Logistic Growth and Carrying Capacity
Population Growth In NaturePopulation Growth In Nature
Fluctuating:• Cycle indefinitely above
and below carrying capacity
Rise and Crash• Rise very quickly, overshoot the carrying capacity, and
then crash
CheckpointCheckpoint
•Why is severe weather considered a density-independent factor?•Why is severe weather considered a density-
independent factor?
Biotic PotentialBiotic Potential
Lesson 4.3 Population Growth
• An organism’s maximum ability to produce offspring in ideal conditions
• Many factors influence biotic potential, including gestation time (time to “be born”) and generation time (span from time of organism’s birth until time it has its own offspring).
• Organisms with high biotic potential can recover more quickly from population declines than organisms with low biotic potential.
ObjectivesObjectives
•Describe the factors that influence a population’s growth rate.• Explain exponential growth and logistic growth.• Explain how limiting factors and biotic potential affect
population growth.
•Describe the factors that influence a population’s growth rate.• Explain exponential growth and logistic growth.• Explain how limiting factors and biotic potential affect
population growth.
