Studying Populations/ Population

Density

How many beans are in the jar?

• With your lab partner…Discuss a way you can find out how many beans are in the jar without dumping the jar.

• You have a limited amount of time to figure it out.

What if I asked you…

• How many beans are in the ‘boxed in’ part of the jar?

Population Density

What is Density

• What is the formula for density?

Population DensityFormula:

Population Density = Total Population/ Total Area

There are 2,000 squirrels living in a 10

x 20 wooded lot. How many squirrels are there per unit?

Scientists studied a 10 x 10 plot of beach soil. They found 150 crabs

living in this plot. What is the density of this

population?

How DO you determine a

population’s size?

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

There are four methods we are going to be discussing:

Direct Observation• Count how many you see. (one by one)

–Good for small #’s and small areas

PROS CONSObvious way Not practical: Cannot do

this in large areas***Reliable because it

isn’t an estimateBest if organism doesn’t

moveLimited view (only as many

as you count)

Examples:

How many in the population of Starfish?

How many in the population of people at the beach?

Indirect Observation• Observe “signs” the organism leaves

behind.• Footprints, nests, etc

PROS CONSSometimes easier to count

signs than mobile organisms

An estimate: need some basic information

Easy calculations to make an estimate

Still hard to do in large areas

Adds to research Signs can be hard to interpret: need basic info

Examples:

How many in the population of bears?

How many in the bird population?

Sampling (Random Sampling)• Make an estimate by counting the number of

organisms in one small area and multiplying it to find the number of organisms in the larger area.

PROS CONSEstimate-made on

reasonable assumptionsEstimate-made on

reasonable assumptionsConcentrate on small area;

multiply to find big areaArea needs to represent

total areaActually counting

organismsNeeds to be random

Examples: How many in the population?

A B C D

1

2

3

4

A B C D

1

2

3

4

Mark-and-Recapture Studies• Collect a group of organisms and label the organisms. Release

them Capture another set, the number re-captured (marked) help indicate the population size.

PROS CONSEstimate-made on reasonable

assumptionsEstimate-lengthy calculations

Can observe health of organisms

Time consuming

Can gather other data at the same time

Dependent on capturing organisms

Assume all organisms have same ability to get captured

Example:

Our Lab on Next week will cover this in more detail!!

Carrying Capacity

• The largest population an area can support.– Can be called:

• Equilibrium or Balance

Depends on resources available, size of population, amount of resources each member is consuming.

Carrying Capacity Analogy

What is the carrying capacity of deer on Walla Walla Island?

Limiting Factors

• An environmental factor that causes a population to decrease (or not grow higher).

– Examples: Food, Water, Sunlight, Oxygen, Carbon Dioxide, Space, Weather Conditions

Populations can Change in Size• Birth Rate- number of births in the population in

a certain time.• Death Rate- number of deaths in the population

in a certain time.--------------------------------------------------------------------

• Immigration- organisms moving into a population (not due to birth)

• Emigration- organisms moving out of a population (not due to death)

Put yourName/Date/Class Period on a

Clean Sheet of Paper

Part 1 # 1-5Part 2 #1-7

Mr. Luce is very concerned with the number of deer in Northeast Ohio and the increase in car accidents. To study this he surveyed 3 communities about their deer populations and found on average 10 deer live per square mile.

1. What method of population study did he use?

2. What could make his result more reliable?

While on vacation Mrs. Goodman wondered how many people used the hotel pool in the morning. When she arrived to sun bathe at noon she counted the towels laying on chairs.

3. Which method of population study did she use?

4. Name one problem that could arise with her data.

Mr. Holman is trying to figure out how many teachers eat in the lunch room each day.

5. What method of population study would be best and why?

Review: 1. What are the four methods of determining

population size?2. Which method would you use if you had a small

area with immobile population?3. Which method would you use if you wanted to

also study the health of the organisms?4. Which method would you use in a large area?5. Which method would you use if you could not

easily see/find the organism?6. Which methods are estimates?7. Which method is most accurate?

Review Answers:1. Direct Observation, Indirect Observation, Random

Sampling, Mark-and-Recapture Studies2. Direct Observation3. Mark-and-Recapture4. Random Sampling5. Indirect Observation6. Indirect Observation, Random Sampling, Mark-and-

Recapture Studies7. It depends on how each method is applied. All methods

have pros and cons. You should pick the method that has the least negatives given the conditions of your study.