GOAL:

To develop an understanding of the interdependence of all organisms and the need for conserving natural resources

Populations are dynamic with identifiable characteristics and measurable growth patterns.

Ecology E2.00 To understand factors that affect populations

2.01 define and demonstrate understanding of:

a. immigration and emigration
b. environmental resistance
c. carrying capacity
d. homeostasis

I. Factors related to population survival
A. Immigration and emigration
B. Environmental resistance
1. Biotic
2. Abiotic

a. Soil
b. Sunlight
c. Rain

3. Density dependent factors
a. Parasitism
b. Stress
c. Predation
d. Competition
1) Intraspecific
2) Interspecific
4. Density independent factors
a. Weather
b. Seasonal cycles
c. Space
d. Human influences
e. Catastrophic events
C. Carrying capacity
D. Homeostasis

COMPONENT OF SCIENCE: Unifying Concepts of Science

GOAL:

To enable students to acquire scientific knowledge by applying concepts, theories, principles and laws from life/environmental, physical and earth/space sciences.

2.5 CHANGE - Interactions within and among systems may result in changes in the properties, position, movement, form, or function of systems.

2.5b Cycles of change can be extended in scales of time, space and material.

BENCHMARK: Interdependence conveys a need for all organisms within the environment to develop a natural, uninhibited, rate of change.

TIME REQUIRED:

120-180 minutes, depending on the number of activities used

Dictionary, biology textbooks, (one currently used at your school or textbook adoption samples work fine), paper, pencils, graph paper, two different colors of rag "flags", copies of activity sheet.

Abiotic factors, biotic factors, carrying capacity, density dependent factors, density independent factors, emigration, environmental resistance, homeostasis, immigration

This classroom connector addresses Instructional Objective 2.01.

During this series of lessons we have been learning about populations and how they can be described and measured. Today we are continuing that study of populations by looking at factors that influence their survival. If we can learn more about plant and animal survival it should help us to live in better harmony with nature. However, now I want you to take time to think about the last time you had people to visit your home for an extended period of time - perhaps overnight. It is possible that you had to give up your favorite chair or even your bed to make room for these visitors. Write some of the feelings you experienced. (Walk around the room to monitor the student's progress. After a minute or two ask some of the students to share some of their responses. Give students an opportunity to comment.)

(List the significant terms on the chalkboard. Divide the students into groups of four and give each group a portion of the terms to define. Have dictionaries, biology texts, etc., available for students to use. After sufficient time, have the groups share their findings with the class, while the others take notes. When you finish each group should have a complete list of definitions for the terms. Now you can lead a discussion demonstrating how these terms are relevant to populations.)

How can the size of populations be changed? (response) That is correct! Natality and mortality were discussed in yesterday's lesson and they certainly would change the size of a population. However, there are two more ways population size may be influenced. Does anyone know? (Call on volunteers or someone else you think would know the answer.) Good! Immigration is one of our words today and would increase the population when individuals move into a new area and take up residence. Can you think of an example? (response)

Another way to influence population size is the opposite of immigration and it is called emigration. An example of this would be a population of squirrels moving from one mountain into another because of a food shortage. Did you think of an example? (Note student responses. If you detect misunderstandings, go back to review the terms before proceeding.)

Environmental resistance is the sum of all the factors that prevents a population from reaching its biotic potential. These factors are divided into biotic and abiotic factors and can also be classified as either density dependent or density independent. Biotic factors are defined as everything in the environment that is alive or was alive. Give some examples. (responses) Good, you have the idea. The abiotic factors that influence population size and distribution are all the things in the environment that are not alive. Examples are the type of soil, fertile valley or rocky slope, etc., the amount of sunlight received each day, and the annual rainfall.

Density dependent factors are dependent on the number of individuals present in the population and include such things as parasitism, stress, predation and competition.

Having large numbers of organisms in the population makes them more susceptible to parasites. Think what a group of fleas could do if they were to make it to a dog show! Diseases are often caused by parasites and in this way help to check the population increase. Stress is another factor that is related to large numbers of organisms. Remember earlier when we talked about all those visitors who came to your house and how you felt. Some of those emotions were stress' related. In some populations birthrates decline when they are stressed or crowded into a confined space.

Populations can also be limited by predation. As the population of prey species increases generally the number of predators will gradually increase also. The reverse is also true. Can you think of some specific examples? (response)

As the density increases so does competition. When organisms use one or more of the same resources it is said to compete. This competition can be with members of its own population, and is called intraspecific competition. An example is a group of black bears trying to find a den. Do you have examples? (response) Sometimes organisms compete with other populations for a resource. This is called intraspecific competition. An example here is an oak and a dogwood competing for the same water, sunlight, and space in the forest.

Density independent factors are those factors that are independent of population size in their influence. Can you think of examples that are density independent? (responses) (Continue to guide their responses with leading questions until you have helped them to "discover" and discuss weather, seasonal cycles, space, human influences, and catastrophic events. Be sure you help students to see how each of these can limit a population.)

With all these factors working together the environment has a maximum number of organisms that it can support. This number is called the carrying capacity. It represents a balance between biotic potential and environmental resistance or the limiting factors. Even given this great number of complex interactions within a community or ecosystem, populations do not usually change rapidly unless there is some major calamity. This ability for nature to maintain her balance is sometimes called homeostasis. The steady state of balance is possible because the system makes adjustments to small imbalances before they become severe.

"Musk Ox Maneuvers" Project Wild (Secondary)

"Oh Deer" Project Wild (Secondary)

"Where Have All The Salmon Gone" Project Wild (Aquatic)

"Owl Pellets" Project Wild (Secondary)

(Closure must be used at the end of each instructional period. Have the students recap what they have learned and how this relates to populations. A good way to do this is to divide the class into two groups. Have one group list what they have learned and the other group share how it relates to the population topics discussed for the day. Share these with the entire class.)

This is the time this file has been accessed since 11/16/96.

The University of Tennessee at Martin is not responsible for the information or views expressed here.

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