Determining Population Size

1
Determining Population Size

• There are four basic Methods that ecologists use
  to determine population size?
• Direct observation
• Indirect observation
• Sampling
• Mark and recapture studies

2
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
3
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
4
Determining Population Size

• Determining the number of frogs in a pond by
  counting all of them individually.

Direct Observation
5
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
6
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.

7
Changes in Population Size

• List 2 ways a population can change in size
• _______________________________
• _________________________________

When new members join the population
When members leave the population
8
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.

9
Changes in Population Size

• Which Two allow a population to increase?
• Birth Rate
• Immigration
• Which two allow a population to decrease?
• Death Rate
• Emigration

10
Changes in Population Size

• What does the population statement say?
• If birth rate gt death rate, population size
  increases.
• If death rate gt birth rate, population size
  decreases.

11
Population Density

• The number of individuals in a specific area.

Number of Individuals
Population Density
Unit Area
12
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
0.5 maples per square meter (m2)
10 square meters (m2)
13
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
14
Limiting Factors

• An environmental factor that causes a population
  to decrease.
• Food and Water
• Space
• Weather

15
Limiting Factors

• Pick one of the limiting factors and describe how
  it limits population growth.
• Food and Water
• Space
• Weather

16
Carrying Capacity

• The largest population that an area can support.
  
• Determined by the limiting factors that are
  present.

17
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