Population and Community Ecology - PowerPoint PPT Presentation


Title: Population and Community Ecology


1
Population and Community Ecology
  • Chapter 6

2
Levels of complexity
  • Individual
  • Population same species, same time, same area
  • Community all the different populations in an
    area
  • Ecosystem all the different communities plus
    the abiotic factors in an area
  • Biosphere all areas on Earth where life exists

3
Population ecology
  • Study the factors that cause population to
    increase and decrease

Input Immigration Births
Output Emigration Deaths
Population size
4
Basic population characteristics
  • Population size total number of individuals (N)
  • Population density number of individuals per
    unit of area
  • Helps us understand if the species is rare or
    abundant
  • Population distribution how individuals are
    spaced relative to others in the population
  • Random no pattern of location (trees in a
    forest)
  • Uniform fairly even spacing (nesting birds)
  • Clumped individuals gather around each other
    (schooling fish)
  • Population sex ratio the ratio of males to
    females
  • Usually 5050
  • Population increase is related to the number of
    females
  • Population age structure the number of
    individuals in each age category
  • Populations with large numbers of young ?
    increasing
  • Populations with large numbers of old ?
    decreasing

5
(No Transcript)
6
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7
Factors that influence population size
  • Density-dependent factors
  • Influence an individuals odds of survival in a
    manner that depends on the size of the population
  • Example available food
  • These factors are also called limiting resources
  • The population limit in an ecosystem is its
    carrying capacity

8
Factors that influence population size
  • Density-independent factors
  • Have the same effect on an individuals odds of
    survival regardless of the size of the population
  • Example a tornado

9
Population growth models
  • Exponential growth model
  • Growth rate number of offspring deaths
  • Under ideal conditions (with unlimited resources)
    each species has a particular intrinsic growth
    rate the max for that species
  • This model calculates this maximum rate and
    displays it as a J-shaped curve (because there
    are no limits)
  • Only beginning populations can actually show this
    type of growth

10
Population growth models
  • Logistic growth model
  • Includes environmental limits on the population
    growth
  • As the population reaches the carrying capacity,
    the growth slows and then stops
  • This produces an S-shaped curve
  • Some populations cycle above and below the
    carrying capacity this is overshoot followed by
    die-off

11
(No Transcript)
12
Reproductive strategies
  • K-selected species
  • Low intrinsic growth rate
  • Slowly reach the carrying capacity and then stay
    there
  • Characteristics
  • Large
  • Later maturing
  • Few offspring
  • Substantial parental care

13
Population growth models
  • r-Selected Species
  • High intrinsic growth rate
  • Rapid population growth followed by overshoots
    and die-offs
  • Characteristics
  • Small
  • Early maturity
  • Small offspring
  • Little or no parental care

14
Survivorship Curves
  • Patterns of survival over time
  • Type I high survival throughout most of their
    lifespan
  • K-selected species humans, elephants
  • Type III low survival early in life few
    individuals reach adulthood
  • r-selected species mosquitoes, dandelions
  • Type II relatively constant decline in
    survivorship throughout their lifespan
  • squirrels, coral

15
Survivorship Curves
16
Metapopulations
  • Smaller, fragmented parts of a larger overall
    population
  • Occasionally members of one metapopulation move
    from one to the other
  • This can reduce the risk of extinction
  • Moving individuals increase genetic diversity as
    well as the size of a population
  • Human development is causing more and more
    metapopulations to form

17
Community Interactions
  • Competition
  • Individuals must fight over the same limiting
    resource
  • Competitive exclusion principal
  • Two species competing for the same limiting
    resource cannot coexist
  • Resource partitioning
  • Two species divide the resource based on
    differences in behavior or morphology
  • This can lead to natural selection which over
    time will increase the differences between the 2
    species
  • Three possibilities
  • Temporal resource partitioning use the same
    resource but at different times (coyotes and
    wolves)
  • Spatial resource partitioning use different
    locations (plants with shallow roots vs. deep
    roots)
  • Morphological resource partitioning evolution
    of different body plans to use different parts of
    the resource (Darwins finches)

18
Resource partitioning
19
Community Interactions
  • Predation - the use of one species as a resource
    by another
  • Four categories
  • True predators kill and eat their prey
  • Herbivores consume plants as prey typically
    only eat some of the plant rarely kill the plant
  • Parasites live on or in a host organism rarely
    causes the death of their host
  • Pathogen disease-causing parasite
  • Parasitoids lay eggs inside another organism

20
Community Interactions
  • Mutualism two species interacting in a way that
    increases the survivability of both
  • Plants and the insects that pollinate them
  • Acacia trees and ants
  • Commensalism one species benefits from an
    association with another but the other is not
    helped nor harmed
  • Birds nesting in trees

21
Keystone Species
  • The species on which the ecosystem stability
    depends removing it leads to instability
  • Food supply species (figs)
  • Predator-mediated competition the predator
    keeps the numbers of the superior competitor in
    check. Without the predator, the competitor
    over-populates the ecosystem (sea stars)
  • Ecosystem engineers create habitat for other
    species (beavers)

22
Keystone Species
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Population and Community Ecology

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Title: Population and Community Ecology


1
Population and Community Ecology
  • Chapter 6

2
Levels of complexity
  • Individual
  • Population same species, same time, same area
  • Community all the different populations in an
    area
  • Ecosystem all the different communities plus
    the abiotic factors in an area
  • Biosphere all areas on Earth where life exists

3
Population ecology
  • Study the factors that cause population to
    increase and decrease

Input Immigration Births
Output Emigration Deaths
Population size
4
Basic population characteristics
  • Population size total number of individuals (N)
  • Population density number of individuals per
    unit of area
  • Helps us understand if the species is rare or
    abundant
  • Population distribution how individuals are
    spaced relative to others in the population
  • Random no pattern of location (trees in a
    forest)
  • Uniform fairly even spacing (nesting birds)
  • Clumped individuals gather around each other
    (schooling fish)
  • Population sex ratio the ratio of males to
    females
  • Usually 5050
  • Population increase is related to the number of
    females
  • Population age structure the number of
    individuals in each age category
  • Populations with large numbers of young ?
    increasing
  • Populations with large numbers of old ?
    decreasing

5
(No Transcript)
6
(No Transcript)
7
Factors that influence population size
  • Density-dependent factors
  • Influence an individuals odds of survival in a
    manner that depends on the size of the population
  • Example available food
  • These factors are also called limiting resources
  • The population limit in an ecosystem is its
    carrying capacity

8
Factors that influence population size
  • Density-independent factors
  • Have the same effect on an individuals odds of
    survival regardless of the size of the population
  • Example a tornado

9
Population growth models
  • Exponential growth model
  • Growth rate number of offspring deaths
  • Under ideal conditions (with unlimited resources)
    each species has a particular intrinsic growth
    rate the max for that species
  • This model calculates this maximum rate and
    displays it as a J-shaped curve (because there
    are no limits)
  • Only beginning populations can actually show this
    type of growth

10
Population growth models
  • Logistic growth model
  • Includes environmental limits on the population
    growth
  • As the population reaches the carrying capacity,
    the growth slows and then stops
  • This produces an S-shaped curve
  • Some populations cycle above and below the
    carrying capacity this is overshoot followed by
    die-off

11
(No Transcript)
12
Reproductive strategies
  • K-selected species
  • Low intrinsic growth rate
  • Slowly reach the carrying capacity and then stay
    there
  • Characteristics
  • Large
  • Later maturing
  • Few offspring
  • Substantial parental care

13
Population growth models
  • r-Selected Species
  • High intrinsic growth rate
  • Rapid population growth followed by overshoots
    and die-offs
  • Characteristics
  • Small
  • Early maturity
  • Small offspring
  • Little or no parental care

14
Survivorship Curves
  • Patterns of survival over time
  • Type I high survival throughout most of their
    lifespan
  • K-selected species humans, elephants
  • Type III low survival early in life few
    individuals reach adulthood
  • r-selected species mosquitoes, dandelions
  • Type II relatively constant decline in
    survivorship throughout their lifespan
  • squirrels, coral

15
Survivorship Curves
16
Metapopulations
  • Smaller, fragmented parts of a larger overall
    population
  • Occasionally members of one metapopulation move
    from one to the other
  • This can reduce the risk of extinction
  • Moving individuals increase genetic diversity as
    well as the size of a population
  • Human development is causing more and more
    metapopulations to form

17
Community Interactions
  • Competition
  • Individuals must fight over the same limiting
    resource
  • Competitive exclusion principal
  • Two species competing for the same limiting
    resource cannot coexist
  • Resource partitioning
  • Two species divide the resource based on
    differences in behavior or morphology
  • This can lead to natural selection which over
    time will increase the differences between the 2
    species
  • Three possibilities
  • Temporal resource partitioning use the same
    resource but at different times (coyotes and
    wolves)
  • Spatial resource partitioning use different
    locations (plants with shallow roots vs. deep
    roots)
  • Morphological resource partitioning evolution
    of different body plans to use different parts of
    the resource (Darwins finches)

18
Resource partitioning
19
Community Interactions
  • Predation - the use of one species as a resource
    by another
  • Four categories
  • True predators kill and eat their prey
  • Herbivores consume plants as prey typically
    only eat some of the plant rarely kill the plant
  • Parasites live on or in a host organism rarely
    causes the death of their host
  • Pathogen disease-causing parasite
  • Parasitoids lay eggs inside another organism

20
Community Interactions
  • Mutualism two species interacting in a way that
    increases the survivability of both
  • Plants and the insects that pollinate them
  • Acacia trees and ants
  • Commensalism one species benefits from an
    association with another but the other is not
    helped nor harmed
  • Birds nesting in trees

21
Keystone Species
  • The species on which the ecosystem stability
    depends removing it leads to instability
  • Food supply species (figs)
  • Predator-mediated competition the predator
    keeps the numbers of the superior competitor in
    check. Without the predator, the competitor
    over-populates the ecosystem (sea stars)
  • Ecosystem engineers create habitat for other
    species (beavers)

22
Keystone Species
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