Transcript Population Ecology

Chapter 52:
Population Ecology
Population Ecology
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Study of the factors
that affect population
size and composition.
Population
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Individuals of a single
species that occupy the
same area.
Important Characteristics
1.
Density
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Number of individuals per unit area or volume.
Ex:
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Diatoms - 5 million/m3
Trees - 5,000/km2
Deer - 4/km2
2. Dispersion
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Pattern of spacing among individuals.
Types:
1. Clumped
2. Uniform
3. Random
Clumped Dispersion
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May result form a patchy environment.
May increase chances for survival.
Ex:
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Schooling behavior
Flocks of birds
Uniform Dispersion
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Often the result of antagonistic interactions
between individuals.
Ex:
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Territories
Spacing between desert plants
Random Dispersion
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Often the result of the absence of strong
attractions or repulsions between individuals.
Not a common pattern.
Demography
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The study of the vital statistics that affect
population size.
Ex: Birth and Death rates
Demographic Factors
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Age structure of the population.
Birth and Death rates.
Generation time.
Sex ratio and reproductive behavior.
Life Tables
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Mortality summary for a cohort of
individuals.
First developed from life insurance studies.
Life Tables Show
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Mortality rate per year.
Life span of the organism.
Fecundity (birth rate).
Survivorship Curve
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Plot of the numbers of a cohort still alive over
time.
Curve Types:
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Type I
Type II
Type III
Survivorship Curves
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Type I
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Low early deaths.
High late deaths.
Ex:
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Humans
Other large mammals
Type II
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Constant death rate.
Ex:
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Annual plants
Many invertebrates
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Type III
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High early deaths.
Low late deaths.
Ex:
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Trees
Oysters
Comment
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Curve type may change between young and
adults.
Ex: Nestlings - Type III
Adult Birds- Type II
Life History Strategies
1. "r" or Opportunistic species
2. "k" or Equilibrial species
"r" Species
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Increase fitness by producing as many offspring
as possible.
Do this by:
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Early maturation
Many reproductive events
Many offspring
Result
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Maximize reproduction so that at least a few offspring
survive to the next generation.
Most offspring die (Type III curve).
"k" Species
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Increase fitness by having most offspring survive.
Do this by:
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High parental care
Late maturation
Few reproduction events
Few offspring.
Result
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Maximize survivorship of each offspring.
Few offspring, but most survive (Type I curve).
What is the strategy
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For a weed?
For an endangered species?
For Garden Pests?
Population Growth
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DN/Dt = b - d
Where:
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N= population size
t = time
b = birth rate
d = death rate
Rate of Increase
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r = difference between birth rate and death
rate.
r=b-d
Equation:
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DN/Dt = rN
N = population size
t = time
r = rate of increase
From Calculus
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The equation DN/Dt = rN
becomes:
dN/dt = rmax N
rmax = intrinsic rate of increase
Exponential Growth
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dN/dt = rmax N
Characteristic of "r" species.
Produces a “J-shaped” growth curve.
Only holds for ideal conditions and
unlimited resources.
Logistic Growth
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dN/dt = rmax N K-N
K
K = carrying capacity
Result
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“S-shaped” growth curve.
Characteristic of “k" species.
Common when resources are limited.
Comment
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K is not a constant value.
Populations often oscillate around “K” as the
environment changes.
Additional Comments
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Populations often overshoot “K”, then drop
back to or below “K”.
AP Exam rarely asks you to work the
equations, but you should be able to give
them.
Regulation of Population Size
1. Density- Dependent Factors
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Affect is related to N (pop. size).
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As N increases, mortality increases.
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Ex: Food, nesting space, disease
2. Density- Independent Factors
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Affect is not related to N.
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Mortality not related to population size.
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Ex: Weather and climate
Population Cycles
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Cyclic changes in N over time.
Often seen in predator/prey cycles.
Ex: Snowshoe Hare - Lynx
Causes
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Density dependent factors.
Chemical cycles.
Saturation strategy to confuse predators.
Age Structure Diagrams
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Show the percent of a population in different
age categories .
Method to get data similar to a Life Table, but
at one point in time.
Importances
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Can be used to predict future population growth
trends, especially for long lived species.
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Exponential Growth
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Produces age structures that are a triangle or
pyramid shape.
Logistic Growth
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Produces age structures that have even sizes
between most age categories.
Declining Populations
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Produce age structures with a narrow base and
wider middles.
Summary
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Know density and dispersion patterns.
Know Life Tables and survivorship curves.
Be able to contrast and compare “r” and
“k” strategies.
Know exponential and logistic growth
curves and equations.
Know density and density-independent
growth factors.