[GHS IB Biology: Ecology & Conservation Unit] --- [Population Review #1] --- [Population Review #2]



Oregon Population Density

Current US Population

Current World Population


Population: All members of 1 species within defined area.

Population Density: # of species members in defined area. May also be described via mass/ area or mass/volume.

Spacing/ Distribution:


Distribution is often determined by needs of the organisms (food, water, mates, shelter, etc..)

Graphing Populations

Natality: Birth rate.

Immigration: Moving in.

Mortality: Death rate.

Emigration: Moving out.

Populations increase when: Natality + Immigration > Mortality + Emigration


s-curve------------------------------------ j- (exponential) curve

Exponential growth phase: Maximum population growth rate.

Transitional phase: Population increases / decreases.

Plateau phase: Steady state. Population in equilibrium. This is the carrying capacity.

Carrying capacity: Max. population size a particular environment can support with no net increase or decrease over a long period of time.

Factors affecting population increase/decrease :

a. male/female ratio

b. age distribution / 3 at reproductive age

c. species density: effects health, food & H20 supply - territory needs

d. climate, availability of shelter, predator numbers, adaptability, means of protection

Reproductive Strategies:

A) r-strategies: Reproductive strategy where the population puts more resources into producing as many offspring as possible in a short period of time. This reproductive strategy is common in unstable or rapidly changing environments. Examples: salmon (those that reproduce only once), protozoa, bacteria. Characteristics of this strategy include:

a) short life span

b) early maturity (they are capable of reproducing very quickly)

c) small body size

d) reproduce only once

e) many offspring produced per reproductive cycle.

B) k-strategies: Reproductive strategy where the population puts more resources into development and long-term survival of each individual. This reproductive strategy is common in stable, unchanging environments. Examples: whales, sharks, humans. Characteristics of this strategy include:

a) long life span

b) late maturity

c) large body size

d) reproducing many times over long periods of time.

e) one or two offspring per reproductive cycle

All populations eventually reach equilibrium with their environment. Those with exponential growth tend to overshoot their carrying capacity & crash back to low #s.

Population Studies

Random Sampling: Method to scientifically estimate population of individuals in an area using a grid. Count individuals in some grids, average, and multiply by total # of grids.

Mark-capture method: Capture & mark individuals. Release. Capture more individuals. Note how many marked individuals there are. Use Lincoln Index below.


Lincoln Population Index: A mathematical model for estimating population size when counting the whole population would be too difficult to do.

Population Size = (n1 X n2) / n3

where: n1 = # caught, marked, & released 1st time.

n2 = # captured 2nd time.

n3 = number of marked individuals caught 2nd time.

[Population Review #1] --- [Population Review #2]