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Chapter 52 (pgs. 1151- 1172) Population Ecology

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Title: Chapter 52 (pgs. 1151- 1172) Population Ecology


1
Chapter 52 (pgs. 1151- 1172) Population Ecology
  • AP minknow
  • How density, dispersion, and demographics can
    describe a population.
  • The differences between exponential and logistic
    models of population growth.
  • How density-dependent and density-independent
    factors can control population growth

2
  • Characteristics of Populations
  • 1.Define the scope of population ecology 
  • 2.Define and distinguish between density and
    dispersion. 
  • 3.Explain how ecologists measure the density of a
    species. 
  • 4.Describe conditions that may result in the
    clumped dispersion, uniform dispersion, and
    random dispersion of populations. 
  • 5.Describe the characteristics of populations
    that exhibit Type I, Type II, and Type III
    survivorship curves.  
  • 6.Describe the characteristics of populations
    that exhibit Type I, Type II, and Type III
    survivorship curves.
  • Life History Traits
  • 7.Define and distinguish between semelparity and
    iteroparity. 
  • 8.Explain how limited resources affect life
    histories. 
  • 9.Give examples of the trade-off between
    reproduction and survival.

3
  • Population Growth
  • 10.Compare the geometric model of population
    growth with the logistic model.  
  • 11.Explain how an environment's carrying capacity
    affects the intrinsic rate of increase of a
    population. 
  • 12.Distinguish between r-selected populations and
    K-selected populations. 
  • 13.Explain how a "stressful" environment may
    alter the standard r-selection and K-selection
    characteristics.
  • Population-Limiting Factors
  • 14.Explain how density-dependent factors affect
    population growth. 
  • 15.Explain how density-dependent and
    density-independent factors may work together to
    control a population's growth. 
  • 16.Explain how predation can affect life history
    through natural selection. 
  • 17.Describe several boom-and-bust population
    cycles, noting possible causes and consequences
    of the fluctuations.
  • Human Population Growth
  • 18.Describe the history of human population
    growth. 
  • 19.Define the demographic transition. 
  • 20.Compare the age structures of Italy, Kenya,
    and the United States. Describe the possible
    consequences for each country. 
  • 21.Describe the problems associated with
    estimating Earth's carrying capacity.

4
  • Population ecology is the study of populations in
    relation to environment
  • Including environmental influences on population
    density and distribution, age structure, and
    variations in population size

5
52.1 Dynamic biological processes influence
population density, dispersion, and demographyA
population
  • A population
  • Is a group of individuals of a single species
    living in the same general area

6
Density and Dispersion
  • Density
  • Is the number of individuals per unit area or
    volume
  • Dispersion
  • Is the pattern of spacing among individuals
    within the boundaries of the population

7
Density A dynamic perspective.
  • Determining the density of natural populations
  • Is possible, but difficult to accomplish
  • In most cases
  • It is impractical or impossible to count all
    individuals in a population
  • Density is the result of a dynamic interplay
  • Between processes that add individuals to a
    population and those that remove individuals from
    it

8
Patterns of Dispersion
  • Environmental and social factors
  • Influence the spacing of individuals in a
    population.
  • There are three different Patterns of Dispersion
  • Clumped Dispersion
  • Uniform Dispersion
  • Random Dispersion

9
  • A clumped dispersion
  • Is one in which individuals aggregate in patches
  • May be influenced by resource availability and
    behavior

10
  • A uniform dispersion
  • Is one in which individuals are evenly
    distributed
  • May be influenced by social interactions such as
    territoriality

11
  • A random dispersion
  • Is one in which the position of each individual
    is independent of other individuals

Figure 52.3c
(c) Random. Dandelions grow from windblown seeds
that land at random and later germinate.
12
Life Tables
  • A life table
  • Is an age-specific summary of the survival
    pattern of a population
  • Is best constructed by following the fate of a
    cohort

13
Survivorship Curves
  • A survivorship curve
  • Is a graphic way of representing the data in a
    life table

14
  • Survivorship curves can be classified into three
    general types
  • Type I, Type II, and Type III

Many species fall somewhere between these basic
types of survivorship curves. Some
invertebrates, such as crabs, show a
stair-stepped curve, with increased mortality
during molts.
Figure 52.5
15
52.2 Life histories are highly diverse, but they
exhibit patterns in their variability.
  • Life histories entail three basic variables
  • when reproduction begins
  • how often the organism reproduces
  • how many offspring are produced during each
    reproductive episode.
  • These histories are evolutionary outcomes
    reflected in the development, physiology, and
    behavior of an organism.
  • Some organisms, such as the agave plant, exhibit
    semelparity. Big Bang Production. (then death)
  • By contrast, some organisms exhibit iteroparity.
  • They produce only a few offspring during repeated
    reproductive episodes.

16
  • Some plants produce a large number of small seeds
  • Ensuring that at least some of them will grow and
    eventually reproduce

17
  • Other types of plants produce a moderate number
    of large seeds
  • That provide a large store of energy that will
    help seedlings become established

18
What factors contribute to the evolution of
semelparity versus iteroparity?
  • In other words, how much does an individual gain
    in reproductive success through one pattern
    versus the other?
  • The critical factor is survival rate of the
    offspring.
  • When the survival of offspring is low, as in
    highly variable or unpredictable environments,
    big-bang reproduction (semelparity) is favored.
  • Repeated reproduction (iteroparity) is favored in
    dependable environments where competition for
    resources is intense.
  • In such environments, a few, well-provisioned
    offspring have a better chance of surviving to
    reproductive age.

19
Population Growth is measured byPer Capita Rate
of Increase
  • If immigration and emigration are ignored
  • A populations growth rate (per capita increase)
    equals birth rate minus death rate

Growth rate rN It can be found using the
equation---
20
Exponential Population Growth
  • Exponential population growth
  • Is population increase under idealized conditions
  • Under these conditions
  • The rate of reproduction is at its maximum,
    called the intrinsic rate of increase
  • Exponential population growth
  • Results in a J-shaped curve

21
The J-shaped curve of exponential growth
  • Is characteristic of some populations that are
    rebounding

22
52.4 The logistic growth model includes the
concept of carrying capacity
  • Exponential growth
  • Cannot be sustained for long in any population
  • A more realistic population model
  • Limits growth by incorporating carrying capacity
  • Carrying capacity (K)
  • Is the maximum population size the environment
    can support

23
The Logistic Growth Model
  • In the logistic population growth model
  • The per capita rate of increase declines as
    carrying capacity is reached

We construct the logistic model by starting with
the exponential model And adding an expression
that reduces the per capita rate of increase as N
increases
24
The logistic growth equation
  • Includes K, the carrying capacity

25
  • The logistic model of population growth
  • Produces a sigmoid (S-shaped) curve

Figure 52.12
26
  • As N approaches K for a certain population, which
    of the following is predicted by the logistic
    equation?
  • The growth rate will not change.
  • The growth rate will approach zero.
  • The population will show an Allee effect.
  • The population will increase exponentially.
  • The carrying capacity of the environment will
    increase.

27
The Logistic Model and Real Populations
  • The growth of laboratory populations of paramecia
  • Fits an S-shaped curve
  • Some populations overshoot K
  • Before settling down to a relatively stable
    density
  • Some populations
  • Fluctuate greatly around K

28
The Logistic Model and Life Histories
  • Life history traits favored by natural selection
  • May vary with population density and
    environmental conditions
  • K-selection, or density-dependent selection
  • Selects for life history traits that are
    sensitive to population density
  • K-selection tends to maximize population size and
    operates in populations living at a density near
    K.
  • r-selection, or density-independent selection
  • Selects for life history traits that maximize
    reproduction
  • r-selection tends to maximize r, the rate of
    increase, and occurs in environments in which
    population densities fluctuate well below K, or
    when individuals face little competition.

Controversy
29
  • 52.5 Populations are regulated by a complex
    interaction of biotic and abiotic influences
  • In density-independent populations
  • Birth rate and death rate do not change with
    population density
  • In density-dependent populations
  • Birth rates fall and death rates rise with
    population density
  • Determining equilibrium for population density

30
Density-Dependent Population Regulation
  • Density-dependent birth and death rates
  • Are an example of negative feedback that
    regulates population growth
  • Are affected by many different mechanisms
  • Competition for Resources
  • Territoriality
  • Health (Disease/Parasites)
  • Predation
  • Toxic Wastes (think bacteria)

31
Competition for Resources
  • In crowded populations, increasing population
    density
  • Intensifies intraspecific competition for
    resources

32
Territoriality
  • Cheetahs are highly territorial
  • Using chemical communication to warn other
    cheetahs of their boundaries

33
Population Dynamics
  • The study of population dynamics
  • Focuses on the complex interactions between
    biotic and abiotic factors that cause variation
    in population size

34
Stability and Fluctuation
  • Long-term population studies
  • Have challenged the hypothesis that populations
    of large mammals are relatively stable over time

35
Extreme fluctuations in population sizeAre
typically more common in invertebrates than in
large mammals
Fluctuating Wind pushing eggs out to
sea Cannibalism
36
Metapopulations and Immigration
  • Metapopulations
  • Are groups of populations linked by immigration
    and emigration
  • High levels of immigration combined with higher
    survival
  • Can result in greater stability in populations
  • Are groups of populations linked by immigration
    and emigration

37
Population Cycles
  • Many populations
  • Undergo regular boom-and-bust cycles
  • Three main hypotheses have been proposed to
    explain the lynx/hare cycles.
  • The cycles may be caused by food shortage during
    winter.
  • The cycles may be due to predator-prey
    interactions.
  • The cycles may be affected by a combination of
    food resource limitation and excessive predation.

38
Limiting Factors
Density Dependant Factors
Density Independent Factors
39
  • 52.6 Human population growth has slowed after
    centuries of exponential increase
  • No population can grow indefinitely
  • And humans are no exception

The Global Human Population
Increased relatively slowly until about 1650 and
then began to grow exponentially
40
Global population Growth Rate
  • Though the global population is still growing
  • The rate of growth began to slow approximately 40
    years ago

41
Age Structure
  • One important demographic factor in present and
    future growth trends
  • Is a countrys age structure, the relative number
    of individuals at each age
  • Usually presented in Pyramids

42
Infant Mortality and Life Expectancy
  • Infant mortality and life expectancy at birth
  • Vary widely among developed and developing
    countries but do not capture the wide range of
    the human condition

43
Global Carrying Capacity
  • Just how many humans can the biosphere support?
  • It is complex and we just dont know, but we
    have.

44
Ecological Footprint
  • The ecological footprint concept
  • Summarizes the aggregate land and water area
    needed to sustain the people of a nation
  • Is one measure of how close we are to the
    carrying capacity of Earth

At more than 6 billion people The world is
already in ecological deficit
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