Grasshopper Mark and Recapture (GMR)*
Type of activity:
- Hands-on activity
- Off site activity
- Field data
- Life Science
- Advanced/AP Biology
- Integrated science, all levels
- Environmental studies
- Special education
This activity helps students estimate the density of a population of insects
(grasshoppers) at a given life cycle stage in a given type of habitat.
Notes for teacher:
The size of a population of organisms is a piece of information that is useful in
many biological and environmental studies. However, it is often difficult to obtain this type of information directly. Therefore, we must obtain our information using a method that allows us to estimate the size of a population. The Grasshopper Mark and Recapture (GMR) Activity employs such a method.
The activity can be used as part of a unit on insects in lieu of or in addition to an
insect collection. It allows students to get outside and to put their hands on and observe
common living creatures. The group work involved requires a team effort, and it is rarely
difficult to keep students on task. Students feel a sense of pride about who caught the most insects. Also, when put in single gender groups, girls tend to participate more enthusiastically. Depending on the ability level of students, the GMR can be preceded by a simulation activity adapted from The Science Teacher (Keefer, J. W., and Kleehammer, D. R. 1990. Predicting Packumin Populations. The Science Teacher. 57:7:26-27.). This activity gives students practice with the concepts and calculations involved by capturing Styrofoam packing-pellet "organisms.
Required of students:
Students must work cooperatively in a group setting. They must be able to measure off a plot of land, handle an insect sweep net, paint a dot on the thorax of several grasshoppers, keep accurate records, and (depending on grade/ability level) use a mathematical formula to calculate population density.
Preparation time needed:
It is best if students have already learned the basics of insect life cycles. Students should
also be introduced to types of population studies, their purposes, and their applications in wildlife biology.
It is preferable to gather materials the day before you do the activity, demonstrate the use
of the equipment, and go over general procedures for the day of the activity. If the activity is to be done off-site, travel arrangements must be made in advance. The activity will require a total of 4 to 5 class periods.
The Grasshopper Mark and Recapture (GMR) Activity is a method of estimating the population size (as in the Lincoln-Peterson Estimate) of grasshoppers and other animals. It is designed to be used as part of a unit on insects in any type of biological science class.
The GMR activity is conducted outside in the fall, in an open field that will remain undisturbed for 1-2 weeks. Students capture grasshoppers and mark them in a way that will not injure them.
The marked grasshoppers from the first sample (M) are released where they were captured. A week or two later, a second sample from the same population is taken (p). Some individuals will be marked, or recaptured (m) from the first sampling, while others will be captured for the first time, and thus will be unmarked. The ratio of marked animals (m) to the total number of animals in the second sample (p) is assumed to be the same as the total number of marked animals (M) is to the total population size (P).
Mathematically m / p = M / P.
Therefore, students can arrange the above equation and use P = (M x p) / m to arrive at a numerical estimate of the total population of grasshoppers.
Materials needed for each group of 4-6 students:
- 2 insect sweep nets
- 4 flags or stakes
to mark sampling plot
- Paint or nail polish
- Paper and pencil
- 1 large plastic container with lid
- 1 metric tape measure
(Or 1 student may pace off the area)
- 1 large sheet
- Field guide to insects
- Mark off a grassy area that is 10m x 10m. Mark corners with flags.
- Two student collectors move through the site vigorously sweeping their nets
through the vegetation. Students begin at opposite sides of the site to avoid driving grasshoppers out of the sampling area.
- Take the animals caught to the side of the sampling plot. Carefully open the
net just enough to catch the grasshoppers one at a time. While one student
holds a grasshopper, another puts a dot of nail polish or liquid paper on its
thorax, being careful not to get the marking substance on the wings or the head.
Put each grasshopper into the plastic container as it is marked. One student must keep a tally of how many grasshoppers are marked (M).
- Repeat steps 2 and 3 two more times.
- Release all grasshoppers into the center of the sampling plot.
- Return to the same plot in 1-2 weeks and repeat the sampling. This time
you will capture some insects that are marked, which have been recaptured
from the original sampling, and some individuals that are unmarked, or captured for the first time.
- Calculate the population size estimate using the equation P = (M x p)/m, where M = the total number of individuals marked in the first sample, m = number of marked individuals in the second sample (marked + unmarked), P = population size estimate ((M x p)/m).
- For advanced classes, see item 6 in Extension section.
Method of evaluation:
- Write a paragraph describing how you felt about handling insects before and
after you participated in this activity.
- Write a "Today I learned... " entry in your journal.
- Write a paragraph explaining what you can learn about grasshoppers by doing the GMR that you can't learn by dissecting them (and vice versa).
- When you are counting the grasshoppers caught in your net, also count all the other insects and arachnids you catch. Using your field guide to identify the animals.
- Identify the species of grasshopper you have caught. Take photos, make sketches,
and find out what species live in other parts of the country via computer network.
- Make a computer database on grasshopper populations to be updated yearly.
- Research other mark and recapture techniques for other animals.
- AP Biology - Discuss in terms of the Hardy-Weinberg Equilibrium assumptions.
- AP Biology and mathematics -- Since the estimate could change from week to week,
depending on the proportion of marked individuals in the second sample, we could
express population size as a range of numbers with 95% degree of certainty.
We can calculate the standard error and confidence range of the data using the following
Standard Error, SE = the square root of (M2 x p (p -m))/m3
The confidence range is the value of the estimated population, P, plus or minus 2 times SE.
Example: If P = 150, and SE = 16, then we can say with 95% certainty that the population size is between 118 and 182 individuals.
*(Adapted by Carolyn S. Nevin, co-author, from the 1993 Curriculum Guide of the Northeast Alabama Network of Environmental Educators)