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Population Ecology
Size, Growth, and Regulation
Associated Reading: 26.1 - 26.2, 26.4
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Courtesy of Joe Robertson, Wikimedia Commons
Courtesy of National Oceanic and Atmospheric Administration
Terms to Know
•Habitat •Population •Community •Ecosystem •Biotic Factors •Abiotic Factors
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Biotic Potential
•Biotic potential: Maximum rate of increase in a
population under ideal conditions
•Varies between species
•In nature, biotic potential is rarely reached
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Population Growth Our hypothetical mouse population
•2,000 individuals
•Reproduce every month
•1,000 births every month
•200 deaths every month
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•Birth rate (b) = # of births Total population size
•Death rate (d) = # of deaths Total population size
b = d = 1,000 2,000
200 2,000
= 0.5 = 0.1
Changes in a Population Over Time
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Rate of change in population size during a
given period of time
•AKA: natural rate of increase
•How quickly a population is growing with each
generation
•Takes into account both births and deaths
r = b - d
r = 0.5 - 0.1 = 0.4
Growth Rate (r)
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Population growth per unit time
(G)
Growth rate
(r)
Total population
(N)
x =
Population Growth (G)
G represents the number of individuals added to a population in the specified time frame
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Month 1 2,000 x 0.4 = 800 mice added + 800 2,800 mice in population by month 2
Month 2 2,800 x 0.4 = 1,120 mice added +1,120 3,920 mice by month 3
Month 3 ???
Apply What You Know
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TIME
PO
PU
LATI
ON
SIZ
E Exponential Growth
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Population growth per unit time
(G) Growth rate
(r)
Total population size
(N) x =
Proportion of resources not
yet used x
Logistic Growth
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An S-shaped growth curve stabilizes at carrying capacity
The S-Curve of Logistic Population Growth
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Overshooting Carrying Capacity
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= Environmental Resistance
Limits on Growth of Populations
Limiting factor: any essential resource that is in short supply
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Total population size
Area of the habitat =
Malheur County 9,930 acres in the SE corner of Oregon
Home to ~10,000 deer
Image courtesy of Google Maps
Density
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Images courtesy of Pixabay.com
Density-Independent Factors
•Factors unaffected by population density.
•Natural disasters, climate changes, etc.
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Image courtesy of U.S. Fish and Wildlife Service
Image courtesy of U.S. Fish and Wildlife Service Public Domain
Image by Karunakar Rayker via Flickr CC BY 2.0
Density-Dependent Factors
•Logistic growth equation deals with density-dependent controls
•Limiting factors become more intense as population size increases
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Images courtesy of Pixabay.com and OpenStax.org
Predator-Prey Cycles
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Human Populations
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Current World Population ←Awesome website alert! Click here for a
real time estimation of the earth's population
Human Population Growth
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The Demographic Transition
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Age Structure Diagram for Sweden
Replacement Level Fertility (RLF)