Studying Populations

1
Studying Populations

• Life Science

2
Determining Population Size

• Scientist use a variety of methods to determine
  population size
• Direct Observation
• Indirect Observation
• Sampling
• Mark and Recapture

3
Observations

• Direct Observation

• Indirect Observation

• The most obvious way to determine population size
  is to count the organisms!
• Examples
• Counting crabs in a tidal pool
• Squirrels in your backyard
• People in this classroom

• Sometimes it is easier to observe signs of
  organisms rather than the organism itself!
• Examples
• Cliff swallows/mud nests
• Can you think of others?

4
Sampling

• Use
• Used when a population is very large or spread
  out.
• Estimate
• An approximation of a number based on reasonable
  assumptions.
• Example
• Counting all of the organisms in a small area and
  then multiplying to find the number in a larger
  area.

5
Calculating Populations

• An oyster bed is 100 meters long and 50 meters
  wide. In a 1 square meter area you count 20
  oysters. Estimate the total population of oysters
  growing in the bed.
• Hint To find the size of the bed you must use
  the following equation length x width area

100 x 50 5000 m2 x 20 100,000 oysters in the
bed.
6
Mark and Recapture

• Mark and Recapture
• Used when a population is spread out or hard to
  observe
• Examples
• Turtles in a bay
• Basking Sharks

7
How would you determine the size of these
populations?

• Oak Trees in the Audobon Sanctuary
• Striped Bass along the North Shore of MA
• Bumble Bees in your back yard.

• Ant colonies next to your driveway.
• Robins living around your house
• Squirrels in Middleton.

In your plan be sure to include How? And Why?
8
Changes in Populations

• Birth Rate
• of organisms born each year
• Death Rate
• of organisms that die each year
• Immigration
• Organisms moving in
• Emigration
• Organisms moving out

9
Graphing Populations
10
The Population Statement

• Population Growth
• Birth Rate gt Death Rate
• Population Decline
• Birth Rate lt Death Rate
• Growth Rate
• Birth Rate-Death Rate
• Example
• BR 1600 Deer
• DR 1400 Deer
• Growth Rate ?

11
Population Density

• Number of Organisms ----------------------------
  ----Unit of Area
• Ex 50 White Sharks per square kilometer
• What are the impacts of a high population density?

12
Limiting Factors

• Definition
• An environmental factor that causes a population
  to decrease
• Examples
• Food
• Water
• Nesting Space
• Mates
• Weather

13
Carrying Capacity

• Definition
• Largest population an ecosystem can support.
• Populations hover around carrying capacity if
  limiting factors dont change.