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 CityManhattan, New York City

70,595 people per sq. mile70,595 people per sq. mile

Dhaka, Bangladesh: 7 million in 59 mi2

Spread of Disease

Lack of Natural Resources

Competition

Lack of Jobs

Crowded Much?!?

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

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?

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

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

Doubling Time

Population Reproductive StrategiesJ-curve (Exponential) = r-selected

Exponential Growth= r-selected

Reproductive Strategies

S-curve (Logistic) = K -selected

Reproductive Strategies

S-curve (Logistic) = K -selected

Reproductive Strategies

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-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

RR

RR

KK

KK

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

•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