Chapter 52 (pgs. 1151- 1172) Population Ecology

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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

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• 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.

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• 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.

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• 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

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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

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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

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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

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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

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

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

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• 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.
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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

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Survivorship Curves

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

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• 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
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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.

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

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

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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.

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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---
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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

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The J-shaped curve of exponential growth

• Is characteristic of some populations that are
  rebounding

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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

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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
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The logistic growth equation

• Includes K, the carrying capacity

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

Figure 52.12
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• 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.

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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

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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
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• 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

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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)

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Competition for Resources

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

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Territoriality

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

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Population Dynamics

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

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Stability and Fluctuation

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

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Extreme fluctuations in population sizeAre
typically more common in invertebrates than in
large mammals
Fluctuating Wind pushing eggs out to
sea Cannibalism
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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

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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.

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Limiting Factors
Density Dependant Factors
Density Independent Factors
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• 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
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Global population Growth Rate

• Though the global population is still growing
• The rate of growth began to slow approximately 40
  years ago

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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

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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

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Global Carrying Capacity

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

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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