Counting Animal Populations
Author: Joyce Brumberger
Through hands-on investigation, students will learn about the method field scientists use to determine the population of a species for a specified study area. Through collaboration they will design and implement their own strategic method for counting the population of students in their school.
What should students know as a result of this lesson?
- Students will learn vocabulary terms abiotic, biotic, and indicator species
- Students will learn how the Mark and Capture system for population studies is conducted
- Students will learn the importance of taking sample sizes that are large
- Students will learn the importance of repetition of experimental data collection
What should the students be able to do as a result of this lesson?
- Students will be able to develop strategies for estimating
- Students will be able to calculate estimated populations using a simple mathematical formula
- Students will be able to design a method of counting the population of students in their school
- 3 large jars of equal size
- Suggested jar contents: M&M's, large jelly beans, gum drops
- Post-it Notes
For each group:
- 1 1000 mL beaker
- 1 500 mL beaker
- Black beans, enough to fill the 1000 mL beaker 1/2 full
- White beans, enough to fill 500 mL beaker 1/2 full
- 1 quart size plastic container
- Aluminum foil squares to cover top of 1000 mL beaker
- Large rubber bands to hold aluminum foil in place
- Baking sheet or other large flat container
- Data Table Worksheet - 1 for each student
Preparation for Engagement:
- Count the number of objects that are placed in each of the three jars and record quantities.
- Prepare the board or a poster board with three columns. Label one column for each jar's content.
Preparation for Exploration - For Each Group:
- Fill the 1000 mL beaker 1/2 full with black beans.
- Fill the 500 mL beaker 1/2 full with white beans.
Cut squares of aluminum foil to fit over the 1000 mL beaker with enough to hang over the sides to be secured with a rubber band.
- Display the three clear jars containing the M&M's, large jelly beans, and gum drops.
- Ask each student to estimate the number of gum drops in the jar and record their estimate and their name on a Post-it note.
- Tell students to post their answers in the Gum Drop column on the board so that the numbers increase in a descending order. Tell them they may have to carefully move Post-it notes so that they can properly place an estimate in the correct order.
- Once all the estimates are posted, reveal to the group the correct number of gum drops. If no one guessed the exact amount, ask the group to help determine which estimate was closest to the actual number, which could be higher or lower than the actual value.
- Recognize the winner(s) with a round of applause.
- Tell students that they will have the opportunity to estimate again, this time with the jelly beans.
- Repeat steps 2-6.
- With the knowledge gained from previous estimates, tell students that they will be given one last opportunity to estimate.
- Repeat steps 2-6
Assessment: Assessment is ongoing as students respond orally and with written estimates during the Engagement phase. Improvement in estimating ability for succeeding jars can be noted for each individual.
- Divide students into groups of three.
- Discuss with students the assumptions that are made with the Mark and Recapture method (see worksheet).
- Tell students that the black beans in the jar represent an animal species in the wild and that the beaker represents the study area in which the animals live.
- Tell students that they are going to conduct two "capture and release" events.
- Provide each student with a "Counting Animal Populations" data table.
- Provide each student with a Mark and Recapture Worksheet which provides the procedures.
Assessment: Assessment is ongoing as students partake in the exercise counting beans and orally discussing findings and recording on worksheet.
- Ask students to relate their experiences when estimating the objects in the jar. Answers will vary, but responses may indicate that as they gained experience with estimating, their accuracy improved.
- Ask students what is the value of estimating. Answers will vary, but the value of estimating allows individuals to determine a quantity without having to count the actual number.
- Ask students what are some ways that estimates can be made. Responses may be that estimates can be made based on visual observations and past experience and/or visual observations and a mathematical formula to help calculate a value.
- Ask the students what factors affected the changes in their total estimated populations for each trial? Most commonly the response is that handful sizes were very inconsistent.
- Review with students the assumptions that were made at the beginning of the exploration.
a. no animals ran out of the study area - emigration
b. no new animals enter into the study area - immigration
c. there were no births - natality
d. there were no deaths - mortality
e. animals did not become "trap happy" - looked for the traps
f. animals did not become "trap shy" - ran away from the traps
- Studies can be conducted using a "closed" system or an "open" system. Ask students to identify the type of system modeled in the Exploration phase. Closed
- Ask students to give an example of a study that might actually be conducted in a closed system. Answers will vary, but one example is the study of a deer population in which an area of many square acres is fenced.
- Ask students to post their percent error on the board or a poster board. Ask students to indicate along side their percentage value whether they took large or small handful samples.
- Ask students to analyze the data posted to determine if any correlations or explanations could be made. Commonly, those who took small handfuls had a larger percent error than those with larger samples. This exemplifies that in science many repetitions of an experiment or a study conducted with large populations result in more accurate information.
- Discuss with students the terms abiotic and biotic. Abiotic factors refer to the non-living physical conditions that affect organisms. Examples are temperature, water, soil, climate, sunlight, pH, wind, and oxygen. Biotic factors refer to the interactions among organisms. Examples are an organism's response to the available food supply or competition for space with its own species or another.
- Ask students what information a population study could provide? Along with the natural fluctuation of populations of species, the study of a specific specie population can help assess environmental conditions. These plant or animal organisms are referred to as "indicator" species because of their low range of tolerance to a specific environmental factor. Lichens are very sensitive to toxic gases and are used to study air pollution. Frogs have very sensitive skin. The development of skin diseases or disorders in large populations reflects changes in UV radiation levels.
Assessment: Students' oral explanations of their data, analysis and conclusion will provide teacher the ability to evaluate their understanding of these aspects of experimentation.
- Working in pairs, instruct students to design a method for calculating the total number of students in their school for the grade.
- Instruct students that their design must be clearly outlined and age appropriate.
- Ask each set of partners to share their design strategies with the whole group.
Assessment: Students' oral explanations of their data, analysis and conclusion will provide the teacher the ability to evaluate students understanding of these aspects of experimentation
Basic math skills - multiplication and division.
Best Teaching Practices
- Learning Cycle
- Science Process Skills
Alignment with Standards
- MS-LS2-2 Construct an explanation that predicts patterns of interactions among organisims across multiple ecosystems.
- MS-LS2-4 Construct an argument supported by empirical evidence that changes to physical or biological components of an ecosystem affect populations.
Common Core Standards:
- RST.6-8.3 Follow preciesly a multistep procedure when carrying our experiments, taking measurements, or performing technical tasks.
- RST.6-8.7 Integrate quantitative or technical information expressed in words in a text with a version ofthat information expressed visually (e.g., in a flowchart, diagram, model, graph, or table).
- RST.6-8.9 Compare and contrast the information gained from experiments, simulations, video, or multimedia sources with that gained from reading a text on the same topic.
- WHST.6-8.2 Write informative/explanatory texts, including the narration of historical events, scientific procedures/experiments, or technical processes.
- Grades 5-8 Content Standard A
- Grades 5-8 Content Standard C
- Grades 5-8 Life Sciences Benchmark D
- Grades 5-8 Scientific Ways of Knowing Benchmark A and B
- Grades 5-8 Scientific Inquiry Benchmark A and B
POne of the most difficult jobs for a wildlife manager is to accurately determine the size or density of a population. Because of the intrinsic difference in life cycles between plants and animals, wildlife managers have developed techniques for counting each group. Plants can be simply counted and reported as so many individuals per square meter or hectare. On the other hand, animals are more difficult to count due to their mobility.
Wildlife managers use a "Mark and Recapture" technique for counting animals. For this method to yield effective results (good population density values), several assumptions need to be considered and controlled. The assumptions are that:
- no animals ran out of the study area - emigration
- no new animals enter into the study area - immigration
- there were no births - natality
- there were no deaths - mortality
- animals did not become "trap happy" - looked for the traps
- animals did not become "trap shy" - ran away from the traps
The assumption, therefore, is that the population being counted is considered static
.neither growing, nor declining or being stressed by the inventory procedure. Managers know this is not realistic; consequently they adjust their values based on the natural history of the organisms and a formula to calculate the population referred to as the Lincoln Petersen method of analysis.
(Total of estimated population) = ((total captured in first trapping) x (total captured in second trapping)) / (Number of marked recaptured)
Students should not put beans in their mouth, nose, or ears.
The sustainability of an ecosystem is a function of the delicate balance between abiotic and biotic factors. Animal populations rise and fall over time based on the degree these factors shift. Slight changes in air or water temperature, for example, could dramatically impact animals with a narrow range of tolerance. A fluctuation in food supply, biotic factor, could increase or decrease the population of a species.
We commonly hear or read statistics about animals that are put on the threatened or endangered species lists. How is the total population of a species determined? Understanding the concept of sampling and the application of simple mathematics in which to analyze the data will help students learn how population studies are conducted and how this information can be effectively used.
Engagement: 20 minutes
Exploration: 60 minutes
Explanation: 20 minutes
Elaboration: 30 minutes to develop method, 1-2 days to collect data and analyze
Printable PDF Worksheets
Counting Animal Populations Data Table
Mark and Capture Worksheet