Download Human Population Growth

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