Ch1S2: Studying PopulationsDiscover Activity

Goal: Determine the Cheerio population size without counting each Cheerio in your jar.

*You can use any of the following to help you: ruler and a beaker

*You will have 2 minutes to complete this activity

*When your 2 minutes is up, record your answer

Now count your Cheerios

How close was your answer?

In this activity you came up with an estimate of the size of the

bean population.

Write a definition of the term estimate based on what you did.

Ch1S2: Objectives

• Explain how ecologists determine the size of a population

• Explain what causes populations to change

• Describe the factors that limit population growth

I. Determining population size

A. Methods include: direct and indirect observations, sampling, and mark and recapture

B. Direct Observation- count all the members. (ex. Try to count all the crabs in a tide pool)

C. Indirect Observation- observe signs of organisms rather than organisms themselves (ex. Counting

holes in swallow nests)

D. Sampling- used when pop. may be too large or spread over a wide area

1. estimate- an approximatenumber, based on reasonableassumptions2. Count # of org. in an area

(sample) and multiply to find # in larger area

3. Ex. A biologist collected 1 gallon of pond water and counted 50 paramecium.  Based on the sampling technique, how many paramecium could be found in the pond if the pond were 20,000 gallons

(100,000 paramecium)

Practice Problem

• An oyster bed is 100 meters long and 50 meters wide. In a 1-square meter are you count 20 oysters. Estimate the population of oysters in the bed. (Hint: Drawing a diagram may help you set up your calculation.)

Answer

Total Population is 100,000 oysters

(100m x 50m = 5,000 m square x 20 oysters per m square)

Why is your answer only a estimate?

E. Mark-and-Recapture Studies- 1st- catch org. 2nd- count, mark and release 3rd- return to location and capture again 4th- count how many have marks and

do not have marks 5th- calculate estimated population

II. Changes in population size

A. Pop. Can change in size when

new members join or leave the pop.

B. Births and Deaths1. Main way to enter a pop.

2. Birth rate - number of births in

a pop. in a certain amount of time.

3. Main way to leave a pop.

4. Death rate- the number of

deaths in a population in a

certain amount of time.

C. The Population Statement

1. If birth rate > death rate, population size increases.

2. If death rate > birth rate, population size

decreases.

Birth rate - death rate = the growth rate

Math Skills

• InequalitiesThe population statement is an example of an

inequality. An inequality is a mathematical statement that compares two expressions.

< (is less than) > (is greater than)

Practice problems

1. 5 ____ -6 2. 0.4 ____ 3/5

D. Immigration and Emigration1. Immigration- moving into a population.

2. Emigration - leaving a population.

E. Graphing Changes in Population

1. changes in pop. size can be

displayed on a line graph

http://phschool.com/webcodes10/index.cfm?wcprefix=cep&wcsuffix=5012&area=view&x=0&y=0

F. Population Density- # of individuals

in an area of a specific size.

1. (Formula)

population density = # of individuals

Unit area

2. Example

You count 20 monarch butterflies ina garden measuring 10 square meters. The population density would be 20 monarchs per 10 square meters, or 2 monarchs per square meter.

III. Limiting Factors -an environmental factor that causes a population to decrease

A. Food & water, space and weather conditions are limiting factors.

B. Food and Water1. Pop. Size usually stays near carrying

capacity b/c of limiting factors in its habitat2. carrying capacity- largest pop. that

an area can supportC. Space- over crowding issues for plants

& animalsD. Weather- ex. Temperature, rainfall, hurricane

or flood.

Elbow Room

Directions:

Each groups task is to put together a small puzzle in your square.

*All of the members MUST stay in the square.

*Time how long it takes to complete

your puzzle.

Elbow Room

1. How long did it take each group to complete the task?

2. How does this activity show that space can be a limiting factor?

3. What is the carrying capacity of puzzle-solvers in a square meter?