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: 7 million in 59 mi 2

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 = r = 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 = t d = 70 r (%) Doubling Time

Population Reproductive Strategies J-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-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

R

R

K

K

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