Determining Population Size There are four basic Methods that ecologists use to determine population size? Direct observation Indirect observation.

Determining Population Size There are four basic Methods that ecologists

use to determine population size? Direct observation Indirect observation Sampling Mark and recapture studies

Determining Population Size Determining the size of ant population by

knowing the number of ants that inhabit one ant hill, and then observing how many ant hills are in one particular area.

Indirect observation

Determining Population Size Ecologists estimate the size of the rainbow trout

population in a lake by catching a small sample, tagging them and then releasing them. They come back three weeks later and catch another sample noting how many trout have tags, and how many do not.

Mark and recapture studies

Determining Population Size Determining the number of frogs in a pond

by counting all of them individually.

Direct Observation

Determining Population Size Estimating the number of daisies in a 100

square meter meadow by counting the daisies in a 10 meter by 10 meter plot, and then multiplying by 100.

Sampling

Putting it all together Direct observation of a population gives you the most

accurate count of a population while indirect observation is more of an estimate. Why would an ecologist use indirect observation instead of direct observation.

• Because it is not always practical to count all the individuals in a population.

Changes in Population Size List 2 ways a population can change in size:

1. _______________________________

1. _________________________________

When new members join the population

When members leave the population

Changes in Population Size Birth Rate

– Number of births in a population over time. Death Rate

– Number of deaths in a population over time.

Immigration– New members move into a population.

Emigration– Members leave the population.

Changes in Population Size Which Two allow a population to increase?

– Birth Rate– Immigration

Which two allow a population to decrease?– Death Rate– Emigration

Changes in Population Size What does the population statement say?

If birth rate > death rate, population size increases.

If death rate > birth rate, population size decreases.

Population Density The number of individuals in a specific area.

Number of Individuals

Unit AreaPopulation Density =

Population Density An ecologist sets out to find out how many red maple

trees are in a forest that is 1000 square meters (m2). He marks off a 10 square meter plot and counts 5 red maples in his plot.

– Calculate the population density per square meter (m2) in the 10 square meter plot.

5 maples

10 square meters (m2)

= 0.5 maples per square meter (m2)

Population Density What would be a good estimate of the number of red

maples in the entire 1000 square meter forest?

What method of study did this scientist use to estimate the population size (hint look at the front of this packet)?

– Sampling

5 maples per 10 square meter x 100 = 500 maples in the forest

Limiting Factors An environmental factor that causes a

population to decrease.– Food and Water– Space– Weather

Limiting Factors Pick one of the limiting factors and describe

how it limits population growth.

Food and Water Space Weather

Carrying Capacity The largest population that an area can

support. – Determined by the limiting factors that

are present.

Putting it all together: Study the graph on page E17 in your reading

packet and answer the following questions – Over how many years was the population

studied? ________

– In what year did the rabbit population reach it's

highest point? _________

– What was happening to the population from year 0 to year 4 of the study? Why?• The population was increasing because

more rabbits joined the population than left it.

• Resources were not limited.

10 years

Year 4

Analyzing population growth curve of rabbits in a meadow.

In h

undr

eds

Human Population – Have we reached carrying capacity?