understanding population growth. population ecology deals with #’s of indiv. in a species how and...
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Understanding Population Growth
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Population Ecology
•Deals with #’s of indiv. in a species
•How and why their numbers are the way they are
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Population Density
# of indiv. of a species
unit of area
• A better way to describe size of a pop.
Manhattan, New York CityManhattan, New York City
70,595 people per sq. mile70,595 people per sq. mile
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Dhaka, Bangladesh: 7 million in 59 mi2
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Spread of Disease
Lack of Natural Resources
Competition
Lack of Jobs
Crowded Much?!?
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Populations Change in Size…
Dependent on:
• Birth rate (b )
• Death rate (d )
• Immigration (i )
• Emigration (e )
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Question: How can you get the growth rate of a
population to slow down? Give reasonable solutions!
Make a list with your partner
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Rate of change ( r ) =
[birth rate (b)-death rate (d )]/1000
r = 40 - 20
1000 1000
r =0.04 - 0.02 x 100 = 2% per year
Growth Rate How fast is pop. growing?
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Growth Rate of a Pop.
r = (b - d ) + (i - e )Total Population (1000)
• Use total pop. when given. If
prob. states per 1000, use 1000.
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Population Momentum• Pop. growth that occurs even if levels of
childbearing immediately declined to replacement level
Older people still have
babies
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Practice: With a 2 % growth rate, the world population will double….
• Time for a pop. w/ a stable growth rate to double in size
Doubling Time =
td = 70
r (%)
Doubling Time
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Doubling Time
Population Reproductive StrategiesJ-curve (Exponential) = r-selected
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Exponential Growth= r-selected
Reproductive Strategies
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S-curve (Logistic) = K -selected
Reproductive Strategies
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S-curve (Logistic) = K -selected
Reproductive Strategies
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Carrying Capacity
K = carrying capacity (Max. pop. of a particular species that a habitat can
support over a given time period.
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Carrying Capacity
• May vary by:
– Seasons
– Changes in environment (fire, storm, etc.)
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R Selected vs K Selected
• R-selected1) Many small
offspring2) Little/no care of
offspring3) Most offspring die
before reaching reproductive age
4) High population growth rate
5) Generalists
• K-selected1) Fewer, larger
offspring2) High parental care3) Most offspring
reach reproductive age
4) Lower population growth rate
5) Specialists
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RR
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RR
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KK
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KK
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What Advantages do R Selected Species
have? What about K? Which would you
rather be???
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Density-Dependent
Controls
• Competition for resources due to land issues
• Ex: Predation, Parasitism, Disease, Poisoning
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Density-Independent
Controls
• Controls on Population not due to space issues
• Ex: Natural disasters
• Ex: Severe weather
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•Proportion of a pop. to survive to breeding age
•Type I= Late loss: K-strategists. •Type II = Constant loss: intermediate
reproductive strategists
•Type III = Early loss: R-strategists
Survivorship
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