populations

1
populations

• Mrs. Spadaro

2
Determining population size

• Direct observation
• Indirect observation
• Sampling
• Mark-and-Recapture Studies

3
Direct Observation

• Count all the members in an area
• How many crabs are in the tidepool
• How many fleas on the dog
• How many flies in the house

4
Indirect Observation

• Observe signs of organisms rather than the
  organisms themselves
• Example Mud nests built by cliff swallows
• Count the entrance holes
• Average family has 2 parents and 2 offspring
• 120 entrance holes
• How many swallows do you think there are?

5
Sampling

• Estimate based on reasonable assumptions
• Count the number in a small area and multiply to
  find the number in a larger area
• Area length x width

6

• Oyster bed is 100 meters long and 50 meters wide.
• In 1 square meter you count 20 oysters.
• A L x W
• A 100 x 50 A 5000 m2
• 5000 x 20 ?
• How many oysters are there in all?

7
Mark-and-Recapture Studies

• Estimate by capturing some of the species and
  marking them without harming them
• Release them again
• Capture another group
• Count the number recaptures and count how many
  have marks on them

8

• Total population number marked x total number
  captured/ number recaptured with marks
• Turtles marked 32
• Total number captured 28
• Number recaptured with marks 15
• Total 32 x 28 896 59.7 60 turtles
• 15 15

9
Changes in Population Size

• Births and Deaths
• Birth rate number of births in a certain amount
  of time
• Death rate number of deaths in a certain amount
  of time
• If the birth rate gt death rate, population
  increases
• If the death rate gt birth rate,
• population decreases

10
Changes in Population Size

• Immigration and Emigration
• Immigration moving into a population
• Emigration moving out of a population

11
Changes in Population Size

• Population Density number of individuals in a
  specific area
• Population Density number of individuals
• unit
  area
• Count 20 butterflies in 10 m2 garden
• Population density 20 2 butterflies/m2
• 10

12
Limiting Factors

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

13
Carrying Capacity

• The largest population that an area can support
• A giraffe must eat 10 kg of leaves each day
• The trees in an area can provide 100 kg per day
  while remaining healthy
• Could 15 giraffes live in this area?
• What is the carrying capacity?