Chapter 1.2

STUDYING POPULATIONS

Review the term “population”

Population – is a group of animals or plants in a specific area.

Numbers of populations

• Scientists like to know the number of populations. They want to know if the number went up or down . OR if the number is the same as 50 years ago.

• There are different ways to figure out the number of populations.

Ways to figure out the number of populations:

Ways:

Direct observatio

n

Indirect observatio

n

Sampling

Mark-and-recapture

studies

Direct observation:

• Counting all the members of population.

Indirect observation:

• Counting the “homes” or signs of animals than animals themselves.

Sampling: • To make an estimate- it is an approximation of

a number, based on reasonable assumptions. Counting number of organisms in a small area, then multiplying to estimate number in larger area.

Mark-and-Recapture Studies: • Scientists catch animals, count and mark them

(first time)• Then, second time in 2 weeks, scientists catch

again, count how many animals have marks and how many are unmarked.

• They use a special formula to figure out the number of population.

Changes in Population Size• Population changes when new people move in

(immigrate) or move out (emigrate)

• Discussion: Why do people immigrate or emigrate?• Answer:

• Scientists look at population to:– Make sure it does not grow TOO BIG

• HARD to find food• DESTROY environment• RUN OUT of water• POPULATION is not disappearing

1. Births and Deaths

Birth rate – number of organisms born in a specific time.

Death rate – number of organisms die in a specific time

Example of birth rate: rabbits make 600 babies a year.Example of death rate: 400 rabbits die in a year

2. The Population Statement

• IF birth rate > death rate THEN population increases

• IF birth rate < death rate THEN population decreases

Math Skills – Inequalities p. 16

• < LESS THAN• > MORE THAN• ½ < 0.75 TRUE/FALSE?• TRUEPractice problems:1. 5 -62. 0.4 3/53. -2-(-8) 7-1.5

Immigration and Emigration

Immigration - moving in the population and increasing that population

Emigration - moving out of population and decreasing that population• WHY?• Food, water, space

• How to show population changes?• USE a GRAPH (see figure 7 on p. 17)• What do the vertical axis of the graph show?• Answer: Number of rabbits• What do the horizontal axis of the graph show?• Answer: Year of study• In what year was rabbit population largest?• Year 4• What was the size of the population that year?• 850,000

Graphing changes in population

Figure 7 Graph p. 17

• From year 0 to 4, more rabbits __________ (joined/left) so population increased.

• From year 4 to 8, more rabbits __________ (joined/left) so population decreased

Calculating Growth Rate p. 17

• Birth rate – number of organisms born in a specific time• Death rate – number of organisms that die in a specific

time• If 1600 geese die and 1400 geese are born,

what is the growth rate that year if growth rate = birth rate – death rate?

• -200• What negative number mean?• Answer: Population decreases

5. Population Density

Definition: Number of organisms in an area of specific size. See figure 8

FORMULA to know population density:

Population density= Number of organisms/ area

More dense vs. less dense

Less dense population

More dense population

Population is the U.S.A.

• Population density= Number of organisms/ area

• Example: 20 per

• What is the population density?

Population density= 20 butterflies/10 square meters (show on board)Population density=2 butterflies per square meter

10 square meters (area)

Matching

1. Population density __X axis2. Organism __number die in specific time3. Count __move out4. Mark and recapture __evidence of population5. Sampling __count in small area first6. Direct observation __one, two, three, four…7. Indirect observation __number in a specific area8. Immigrate __living thing9. Emigrate __mark and count10. Birth rate __count one by one11. Death rate __move in12. Vertical axis __# born in specific time13. Horizontal axis __Y axis

Limiting Factors

Definition

• Something that limits the growth of the population

What can limit?

• food• water• living space• weather

Carrying Capacity

• Definition: maximum number land can support

• Example: population cannot increase more than 10 animals

Questions: When might an ecologist use indirect observation to estimate a population?

What does the word “population density” mean?

What is the limiting factor? List the limiting factors.

What is carrying capacity?

What are 4 ways to determine a population size?

What is immigration and emmigration?

What is an estimate and what method uses estimate?

Section 2 Assessment pg 20

1a. What are 4 methods of determining population size?1b. Which method would you use to determine the number of mushroom growing on the floor of a large forest? Explain. 2a. Name two ways organisms join a population and two ways organisms leave a population.

Con’t.2b. Suppose a population of 100 mice has produced 600 young. If 200 mice have died, how many mice are in the population now? 2c. Suppose that you discovered that there were actually 750 mice in the population? How could you account for the difference? 3a. Name 3 limiting factors for populations3b. Choose one of the limiting factors and describe how it limits population growth. 3c. How might the limiting factor you chose affect the pigeon population in your town?

• Copy the data table • Data table shows first

three years1.• Year 4 shows 15

turtles marked in data table

• Select 1 turtle from box X10

2. Record 10 under Total Number Captured

column3.

• WHAT is Mark and Recapture?• Each square is a turtle• Each square with a dot is a marked turtle

From the 10 that you captured, count how many were marked4.

Record number of marked turtles under Number Recaptured

column5.Formula for last column

is number marked x total number captured

/number recaptured (#1 p. 21)

6.

Year Number Marked Total Number Captured

Number Recaptured

Estimated Total Population

1 32 28 15 60

2 25 21 11

3 23 19 11

4 15

Estimated Total Population = Number marked x Total number captured

Number Recaptured

Example using Year 1: 32x28

15= 59.7 or 60 turtles

Make a graph: x axis is year and y axis is population

size7.

Explain how turtle population changed and why you think it

changed8.

Predict what will happen in year 5.

Why you think that way?

9.

Write a paragraph explaining why mark

and recapture is a good way to track

turtles10.