Ecology Populations

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Ecology- Populations -
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Populations

• POPULATION
• A group of individuals of a single species living
  in the same general area.

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Populations - Characteristics
Attributes of Populations
1. Dispersion
- a measure of how organisms are distributed in
space
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Populations - Characteristics
1. Dispersion - can be Clumped
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Populations - Characteristics
1. Dispersion - can be Uniform
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Population Characteristics
1. Dispersion - can be Random
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Population Characteristics
Scale is important in dispersion
Uniform
Clumped
Clumped
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Population - Characteristics
2. Density
Number of organisms/unit area
Measurement depends on dispersion
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Population - Characteristics
2. Density
Immigration
Births
Population size
Emigration
Death
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Population - Growth
Factors which lead to population increase Birth
Immigration
Factors which lead to population decrease Death
Emigration
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Population - Growth
During any time interval
Change in population size in the time interval
Number of births in the time interval
Number of deaths in the time interval
-

DN Dt
-

B
D
(D or delta just means change)
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Population - Growth
We usually express birth and death as a rate per
individual
b the per capita birth rate so 40 births for
every 10,000 individuals is a birth rate of b
.004
m the per capita death rate so 10 deaths for
every 10,000 individuals is a death rate of m
.001
Note we do this so we can directly compare
populations of different sizes
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Population - Growth
This means that B bN
and that D mN
Birth rate
Death rate
Number of births
Population size
Number of deaths
Population size
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Population - Growth
Now our original population growth equation
DN Dt
-

B
D
Can be re-written as
DN Dt
bN - mN

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Population - Growth
And just to make it a bit simpler
b - m can be rewritten as r - the per capita rate
of increase
DN Dt
DN Dt
rN

bN - mN

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Population - Growth
DN Dt
rN

Is the same as
dN dt
rN

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Population - Growth
We finally get to the first kind of growth
equation Exponential population growth
-this assumes that populations will grow at their
maximum rate - rmax
So
dN dt
rmaxN

This means that in a given period of time (t) a
population will add a number of individuals equal
to its growth rate times the number of organisms
in the population
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Population - Growth
What does exponential growth look like?

• Kind of like a snowball effect
• starts slow but gets bigger
• at an increasing rate

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Population - Growth
What does exponential growth look like?
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Population - Growth
This can apply to any species
Human
Only difference is the time
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A Problem
Imagine you are studying a population of 1932
wombats
In one year - 73 births
- 38 deaths
Whats the change in the population size?
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A Problem
Imagine you are studying a population of 1932
wombats
b birth rate 73/1932 .0377
m death rate 38/1932 .0248
r(per capita or intrinisic rate of increase)
b - m .0377 - .0248 .0129
DN Dt
rN

.0129 x 1932 25
Next year the population is 1932 25 1957
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In year 2 - assume the same death and birth rates
Add - 1957 x .0129 25.2 individals
Year Begin End
After 100 years - 6,879.5 wombats
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Population - Growth
A second kind of population growth
From Gauses Paramecium experiments
?
P. aurelia alone
P. caudatum alone
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Population - Growth
A second kind of population growth
From Gauses Paramecium experiments
P. caudatum alone
P. aurelia alone
LOGISTIC POPULATION GROWTH
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Population - Growth
LOGISTIC POPULATION GROWTH
exponential
K - carrying capacity of the habitat
logistic
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Population - Growth
LOGISTIC POPULATION GROWTH
Remember equation for exponential growth
dN dt
rN

How do you get the line to flatten out??
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Population - Growth
LOGISTIC POPULATION GROWTH
How do you get the line to flatten out??
dN dt
(K - N) K
rN

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Population - Growth
LOGISTIC POPULATION GROWTH
What does this mean?
dN dt
(K - N) K

rN
Scenario 1 Population has just started growing
so N is small If N is small, this expression
is close to 1
Say K is 2000 and N 4 critters That would
make equal to 0.998 (or nearly1) and the
growth is close to exponential
(K - N) K
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Population - Growth
LOGISTIC POPULATION GROWTH
What does this mean?
dN dt
(K - N) K

rN
Scenario 2 Population is close to K so N is
large If N is large, this expression is close to
0
Say K is 2000 and N 1987 critters That would
make equal to 0.0065 (or nearly0) and the
growth is close to zero
(K - N) K
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Population - Growth
LOGISTIC POPULATION GROWTH
dN dt
(K - N) K

rN
(K - N) K
In this area is close to 0
(K - N) K
In this area is close to 1
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Population - Growth
LOGISTIC POPULATION GROWTH
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Population - Growth
The growth of a population can be influenced
by Demography - the vital statistics - specific
birth and death rates for organisms at a
particular ages.
Type I death rate higher in older indviduals
Type II death rate consistent
Type III death rate higher in younger
individuals
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Population - Growth
Growth of human populations
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Population - Growth
Growth of human populations
Why?
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Population - Growth
Growth of human populations
Chad
Canada
Italy
Egypt
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Population - Growth
Growth of human populations
Wheres it going??
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Population - Growth
Growth of human populations
Effects are different for each country