What Were They Thinking?
Text Readings
Chapter Reading:
Chapter #26 in Audesirk, Audesirk and Byers:
“Population Growth and Regulation”
Pg. #513-534.
The Misnamed Extinct
“Irish Elk”
~ 4 meters
Source: http://www.ucmp.berkeley.edu/mammal/artio/irishelk.html
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Questions to Answer
in the Chapter
• How Does Population Size Change? p. 514
• How Is Population Growth Regulated? p. 515
• How Are Populations Distributed
in Space and Time? p. 524
• How Is the Human Population
Changing? p. 526
Population Ecology
“. . . .in nature
plants and animals
produce far more
offspring than can
survive, and that
Rev. Thomas Malthus
(1766-1834)
(hu)man, too, is
capable of overproducing if left
unchecked”
Essay on the Principle of Population (1798)
Population Ecology
Population: A group of individuals of the same
species occupying a particular place at a particular
time.
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Population Dynamics
Populations (N) estimates can be
based on:
- Abundance (“Size or Numbers”)
- Distribution (Area)
- Density (#/Area)
Population Dynamics
The study of changes in the
number and composition in a
population, and the factors
that influence those changes.
1. Population Growth/Decline
A.
B.
C.
D.
E.
2. Population Demography
Birth rates (+)
Death rates (-)
Dispersal - (Emigration [-] & Immigration [+])
Sex Ratio
Age Structure
Population Dynamics
Formula:
Population (N) = (B – D) + (I – E)
A closed population:
Population (N) = (B – D)
Biotic Potential
r
or
Rate of Growth/Decline
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Population Dynamics
Population Growth/Decline is dependent upon:
1. The size of the initial population at the
beginning of the time period.
2. The rate of growth or decline,
r, is based on estimated
per capita (per 1,000
individuals) rates.
Population Dynamics
Thus,
Population change can be estimated
from the beginning of 1 time period
to the end. . . .
N t = r N0
Ending of time period
(new estimate)
Beginning of time period
Known as the Malthusian parameter
Aahhhh. ……The good Rev. Thomas Malthus
Population Dynamics
An Example:
Q: What is the world estimated population
abundance of humans by mid-year 2050?
Formula:
Nt = N0e r t
Nt = N2050 = Unknown (?)
N0 = N2005 = 6,477,450,857
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Population Dynamics
An Example:
Q: What is the world estimated population
abundance of humans by mid-year 2050?
Formula:
Nt = N0e r t
e = 2.71828
t = 45 years
r = ? (b – d) (per capita birth and death rates)
Population Dynamics
An Example:
Q: What is the world estimated population
abundance of humans by mid-year 2050?
Formula:
Nt = N0e r t
r = ? (b – d) (per capita birth and death rates)
b = per capita birth rate (annual number of
births per 1,000 total population)
d = per capita death rate (annual number of deaths
per 1,000 total population)
Population Dynamics
An Example:
Q: What is the world estimated population
abundance of humans by mid-year 2050?
Formula:
r = (b – d) = 0.0220 – 0.0090 = 0.0130
b = 21 = 21/1000 = 0.0220
d = 9 = 9/1000 = 0.0090
Extracted from
Data
Source: http://www.prb.org/datafind
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Population Dynamics
An Example:
Q: What is the world estimated population
abundance of humans by mid-year 2050?
Formula:
Nt = N0e r t
N2050 = 6,477,450,857 x
N2050 = 6,477,450,857 x
N2050 = 6,477,450,857 x
N2050 = 11,626,965,898
(2.7183)(0.0130)(45)
(2.7183)(0.5850)
(1.7950)
Population Dynamics
Exponential Growth (unlimited resources)
Nt = N0e r t
Abundance
r = biotic potential
growth rate
t = time period
(e.g., annually,
monthly, daily,
hourly, etc.
Time
Population Dynamics
Sooo…….
What if
resources
become
limiting?
“J” Crash
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Population Dynamics
In Summary:
•
•
•
•
•
The Definition of a Population.
The Factors for Growth/Decline.
Exponential Growth (Unlimited Resources).
The Graph Shape.
How Do Populations Respond Under
Limited Resources?
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