1. How Do Living Things Affect One Another?
Ch. 14.4
Ms. De Los Rios
7th Grade
Populations
Pgs
Essential Question:
How Do Living Things Affect One Another?
How Do Populations Change in Size?
What Factors Limit Population Growth?

2. Vocabulary
Birth Rate- the number of births in a specific population in a certain time period.
Death rate- The number of deaths in a specific population in a certain time period.
Immigration- Movement of individuals into a population’s area.
Emigration- Movement of individuals out of a population’s area.
Population density- the number of individuals in an area of a specific size.
Limiting Factor- an environmental factor that causes a population to decrease in size.
Carrying capacity-the largest population that a particular environment can support.

3. How Do Populations Change In Size? Pg. 500
Populations change in size when new members join the population or when members leave the population.
Ecologist study pop. and monitor the sizes of pop. over time.
new members are born into it (join)
Populations change in size when:
or when members die (leave)
Birth and Deaths
The birth rate counts number of births in a population over a certain amount of time. The death rate counts the number of deaths over a certain amount of time.
Do the MATH!

4. The Population Statement pg. 502
When the birth rate is greater than the death rate, the population will generally increase.
Birth rate > death rate= population will generally increase
The population will generally decrease when the death rate is greater than the birth rate.
Death rate > birth rate= population size decreases
For example, the white-tailed deer population in Iowa decreased due to over-hunting.

5. Immigration and Emigration pg. 502
The population can also change when individuals move into or out of the population.
Immigration means moving into a population
Emigration means leaving a population. Ecologists can graph how a population changes over time.

6. Changes in a Rabbit Population
Populations pg. 503
Changes in a Rabbit Population
This graph shows how the size of a rabbit population changed over ten years.
Fig. 2
Population
In Year_______, the rabbit population reached its highest point.
What was the size of the rabbit population in that year?_____________
How do you think the rabbit population affected the fox population over the same ten-year period. Explain your reasoning.______________________________________

7. Population Density pg. 504
The population density is a measure of all the individuals in one area at one time.
Equation
Population Density= Number of ndividuals
Unit area

8. Populations pg. 504 s. Population Density of the Flamingos in the Pond
In the pond on the top, there are 10 flamingos in
8 square meters. The population density is 1.25 flamingos per square meter. s.
Calculate- What is the pop. Density of the flamingos in the pond on the bottom?
Infer- If 14 more flamingos landed in the pond on the bottom, what would the population density be then?
Challenge- What do you think would happen if the population density of flamingos in the pond on the bottom became too great?
Assess your Understanding

9. What Factors Limit Population Growth? Pg. 509
A limiting factor is something in the environment that keeps a population from growing or makes a population smaller.
Some limiting factors are:
food-
shelter
water
space
disease
parasitism
predation
nesting sites.

10. Factors that Limit Population Growth pg. 505
When there is not enough food, shelter, or water for organisms to survive, population growth can be limited. Limiting factors determine an area’s carrying capacity.
Carrying capacity is the largest population that an area can support.
For example, a plant needs to grow in a large enough space to obtain the things it needs to survive. Also, in densely populated areas disease can spread and infect close-growing plants.
Shelters provide for protection and survival, if organisms can’t find a shelter they may die or lose their young (affecting the pop.)
Water- the quantity and quality of water can mean the difference between life and death. (drought=less water= affects pop.)
Poor water quality= threatens living conditions= poor health
Figure 3

11. Relate Cause and Effect
Populations pg. 505
Relate Cause and Effect
As you read about the four factors that can limit populations, think about cause and effect.

12. Did You Know? Pg. 506
Some plants, like the black walnut tree, release chemicals into the environment that prevent other plants from growing too close. This process is called allelopathy (uh lee LOP uh thee).

13. Factors that Limit Population Growth Pg. 507
Size- space affects animal and plant populations. Amount of space determines whether a plant can obtain light, water, and soil nutrients.
Disease- a limiting factor especially in densely populated areas. During warm and rainy periods some crops can develop disease called early blight (leaves rot and fall off killing the plant.)
Predation can limit the population sizes of prey, while parasitism can reduce the size of the host population.
The availability of nesting sites also limits populations. Without room to nest, offspring cannot be added to a population.
Figure 4

14. Assess your Understanding!
Apply It!! Pg. 507
Read pg. 507
Write a letter to the editor that describes how food and space may be limiting factors for the Florida panther. Add a headline to your letter.
____________________________________________________________________________________________
Assess your Understanding!