Population%20Biology

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Population Biology

• BCOR 012
• Chapter 53

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Note The Tri-Beta honors society will be having
its regular intro bio tutoring sessions Monday
and Tuesday after break, 6 - 8pm in Rowell 244.
This is in addition to the regular Sunday
sessions in Living and Learning.
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Ecology - the study of the interaction between
organisms and their environment
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Ecology and evolutionary biology are closely
related disciplines events that occur in
ecological time affect life on the scale of
evolutionary time. Put another way, an
important cause of evolutionary change is the
interaction of organisms with their environment.
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The focus of ecological studies occurs at many
different scales.
Organismal ecology
Population ecology
Community ecology
Ecosystem ecology
Landscape ecology
Global ecology
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Population Ecology Chapter 53 I. Characteristics
of Populations A. Introduction B. Two important
characteristics of populations are density and
the spacing of individuals ( dispersion) C.
Demography II. Life Histories A. Natural
selection favors strategies that maximize and
individuals fitness. B. Reproductive
strategies C. Trade-offs between reproduction
and survival
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Population ecology is concerned with

• measuring changes in population size and
  composition
• identifying the ecological causes of such
  fluctuations

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From Chapter 23
So what is a population?
A population is a set of individuals of the same
species that live close enough together to
interbreed.
in a particular geographic area.
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Density the number of individuals per unit area
Aerial census of African water buffalo in the
Serengeti
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Dispersion the spacing among individuals within
the population boundaries
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Demography

• Study of the vital statistics of populations and
  how they change over time
• Birth and Death rates

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A life table follows fate of a cohort from birth
to death
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Idealized survivorship curves

• Type I
• Few offspring with good care (mammals)
• Death rate low until older ages
• Type II
• Intermediate (rodents, annual plants)
• Death rate constant
• Type III
• Many offspring with little care (marine
  invertebrates, long-lived plants)
• Initial death rate high, then low

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Population Ecology Chapter 53 I. Characteristics
of Populations A. Introduction B. Two important
characteristics of populations are density and
the spacing of individuals ( dispersion) C.
Demography II. Life Histories A. Natural
selection favors strategies that maximize an
individuals fitness. B. Reproductive
strategies C. Trade-offs between reproduction
and survival
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Life history - the set of traits related to
reproduction, including frequency of
reproduction, number of offspring, investment in
parental care, etc.
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Fitness involves both individual survival and the
production of viable offspring that will live to
reproduce themselves.

• Therefore, why not a life history strategy that
  involves early
• reproductive maturity, frequent reproduction, and
  many offspring
• per brood?

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A. Trade-offs between reproduction and survival
Survivorship vs. brood size in European kestrel
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Population Ecology Chapter 53 III. Population
Growth A. Exponential Growth B. Logistical
Growth IV. Population Limiting
Factors A. Density dependence B. Population
fluctuations C. . V. Human Population
Growth A. Earths carrying capacity B. What can
you do?
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Population Growth

• Growth rate results from processes that add and
  remove individuals

Births
- Deaths
Immigration
- Emigration
Therefore r (bi) - (de)
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r is the per capita growth rate, r b - d,
where b is the per capita birth rate and d is
the per capita death rate
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Clicker Question
 Kingfish, Louisiana, had a population of 1,100
individuals. They had a birth rate of 12/100, a
death rate of 8/100, and an emigration
(individuals leaving the population) rate of
2/100. How many people were added to Kingfish's
population in one year?
What is r?

1. 0.02
2. 22
3. 44
4. 2
5. Not enough information given

r (bi) - (de)
r 0.12 - (0.080.02) 0.02
rN(0.02)(1,100) 22
good job!
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As b decreases and/or d increases, r, the per
capita growth rate, decreases.
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The carrying capacity (K) of an environment is
the maximum population size that the environment
can sustain with no degradation of the habitat.
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As the population size (N) approaches carrying
capacity (K), the population growth rate
approaches zero.
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The Logistical Growth Equation
?K - N? ? K ?
dN dt
rmaxN
By multiplying the exponential rate of increase
rmaxN by (K - N)/K, we reduce the actual growth
rate of the population as N increases.
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The logistic model of population growth produces
a sigmoid (S-shaped) curve when N is plotted over
time.
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How well do actual populations fit the logistical
model?
This laboratory population of Paramecium grew
according a logistical model.
This laboratory population of Daphnia overshot
carrying capacity.
And this natural population of song sparrows
fluctuated considerably in response to
environ- mental stresses.
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Population Ecology Chapter 53 III. Population
Growth A. Exponential Growth B. Logistical
Growth IV. Population Limiting
Factors A. Density dependence B. Population
fluctuations V. Human Population
Growth A. Earths carrying capacity B. What can
you do?
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Density-dependent factors limiting population
growth

• Plants light, nutrients, water
• Animals food, water, nesting/breeding sites
• Increased predation
• Accumulation of waste in the environment
• Increased transmission of disease
• Stress

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Fluctuation in a moose population on Isle Royale,
Lake Superior
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Population Ecology Chapter 53 III. Population
Growth A. Exponential Growth B. Logistical
Growth IV. Population Limiting
Factors A. Density dependence B. Population
fluctuations V. Human Population
Growth A. Earths carrying capacity B. What can
you do?
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The human population has been growing
exponentially, though the rate has slowed in
recent decades
Where is K???
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In the U.S., our ecological footprint is large
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So what can you do about it?

• Live sustainably
• Use resources wisely
• Eat more vegetable protein and less meat
• Support global family planning efforts
• Work for peace and justice

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Two's company ...
6,600,000,000 is a crowd!