1. Studying Populations
Level 2
Section 2 Notes

2. Do NOW: What’s the Population of Beans in a Jar?
Your goal is to determine the bean population size, but you will not have time to count every bean.
You may use a ruler, a small beaker, or another larger jar to help you count the bean population.
You have two minutes to estimate the bean population using a technique of your choice.
Count the actual number of beans. Were you close? How effective was your technique?

3. Determining Population Size
Direct Observation – Counting all of the members of a population.
Ex: Counting all of the crabs in a tide pool.
Indirect Observation – Observing the signs of organisms rather than the organisms themselves.
Ex: Counting bird nests rather than the actual bird.

4. Determining Population Size-Continued
3. Sampling – Count the number of organisms in a small area (a sample), and then multiply to find the number in a larger area.
*This will give you an estimate – and approximation of the population based on reasonable assumptions.
*This is best to use when the population is very larger and/or spread out over a large area.
*Be sure to make sure your sample area is typical of the larger area.
Ex: Number of trees in a forest.
4. Mark-and-Recapture Studies – Scientists capture organisms without harming them, mark them, and release them back into the ecosystem. After some time, they capture more of the same species and check for the mark. Using an equation, scientists can estimate the population size.
Ex. The number of turtles in a pond; number of sharks in the ocean.

5. What would you use to determine the population of the following organisms?

6. Changes in Population Size
3. Populations can change in size when new members join the population or when members leave the population.
The main way that new individuals join a population is by being born in to it. The main what that individual leave a population is by dying.
Birth Rate – the number of births in a population in a certain amount of time.
Death Rate – the number of deaths in a population in a certain amount of time.

7. Is the Mallard Duck population on the pond increases or decreasing?
In 2013 an ecologist studied a population of Mallard Ducks living on the pond near his house. He observed that 32 baby ducks hatched and survived until the end of the year. He also observed that 13 ducks died.
What is the birth rate? 32
What is the death rate? 13
Is the Mallard Duck population on the pond increases or decreasing?
It is increasing because the birth rate is greater than the death rate.

8. Immigration vs. Emmigration
5. Immigration means moving to a population; emigration means leaving a population. A. The same ecologist that studied the birth rate and death rate of ducks on a pond near his house observed that 5 new adult ducks joined the population. He also observe that 18 of the ducks flew away and never came back. How many of the ducks immigrated? 5 How many of the ducks emigrated? 18 *Taking everything into consideration, is the duck population increasing or decreasing?

9. Population Density
The number of individuals in an area of a specific size.
Number of Individuals
Population Density = Unit of Area
*Why do you think it is important for ecologists to study the population density of a species?

10. Limiting Factors
A limiting factor is an environmental factor that causes a population to decrease.
A. Some limiting factors for populations are food and water, space, and weather conditions.
B. The largest population that an area can support is called its carrying capacity.

11. 8. Limiting Factors
Food and Water – Organisms require food and water to survive. Since food and water are often in limited supply, the amount of these resources will limit the size of the populations living in the ecosystem.
Space – Organisms also require space for their habitat or room to grow. Plants are often limited by how much space is available. Birds nesting on a rocky cliff will have limited space. If there is no room for a new nest, then space is a limiting factor for the bird population.
Weather – Temperature and amount of rainfall can also limit the size of a population. Hurricanes and floods can have long lasting effects on population size because they wash away nests and burrows.

12. Exit Slip
What are four common limiting factors? What do you think the limiting factors of a rainforest ecosystem would be? Give an example of a specific population that would be limited by a specific factor. Explain how they would be limited.
-or-
Explain the difference between carrying capacity and population density. Why do you think ecologists study these two aspects of a population?