COUNTING POPULATIONS

Estimations & Random Samples

What are the 3 biggest populations in this pond community?

Name of Population

Ducks Cattails Water Lilies

Actual Count

Sample Count

ACTUAL COUNT

• Each member of a population is counted one by one

Name of Population

Ducks Cattails Water Lilies

Actual Count

6 20 4

Sample Count

Which population was easiest to count?

Why?

RANDOM SAMPLES•Make a GRID

•Count the total number of squares in the grid

•Choose one square of the grid at random.

•Count the population in that one square.

•Estimate the total population by multiplying the number in one square times the total squares in the grid.

RANDOM SAMPLES

Name of Population

Ducks Cattails Water Lilies

Actual Count

6 20 4

Sample Count

1 x10 = 10 3 x 10 = 30 1 x 10 = 10

ACCURACY???

Scientists help prevent over- and under-estimation by taking

several samples and averaging the results.

QUESTIONS

• Why is a sample a good way to count a population?

• What are some disadvantages to using a sample?

• What could you do to sample a population of animals that do not stay in one place?

More on Ecological Statistics…

• Population Statistics

Carrying Capacity: the maximum

population size the environment can

sustain indefinitely given food, habitat,

water, and other necessities available in

the environment

Types of growth

Exponential Linear

Population Growth Curve