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 Density Formula: Population Density = Total Population/ Total Area

There are 2,000 squirrels living in a 10 x 20 wooded lot 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 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? There are four methods we are going to be discussing: Direct Observation Indirect Observation Sampling Mark-and-Recapture Studies

Direct Observation Count how many you see. (one by one) Good for small #’s and small areas PROS CONS Obvious way Not practical: Cannot do this in large areas ***Reliable because it isn’t an estimate Best if organism doesn’t move Limited 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. PROS Footprints, nests, etc PROS CONS Sometimes 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 CONS Estimate-made on reasonable assumptions Concentrate on small area; multiply to find big area Area needs to represent total area Actually counting organisms Needs to be random

Examples: How many in the population? A B C D A B C D 1 2 3 4 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 CONS Estimate-made on reasonable assumptions Estimate-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 your Name/Date/Class Period on a Clean Sheet of Paper Part 1 # 1-5 Part 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. What method of population study did he use? 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 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 Studies 2. Direct Observation 3. Mark-and-Recapture 4. Random Sampling 5. Indirect Observation 6. Indirect Observation, Random Sampling, Mark-and-Recapture Studies 7. 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.