Food Web Game and Ecological Sampling Lab Guide

Food Web Game and Ecological Sampling Lab Guide

The earth is the Lord’s, and everything in it, the world, and all who live in it; for he founded it on the seas and established it on the waters. – Psalm 24: 1-2

Introduction

I. Food Web Game – Take My Energy, Maybe?

Trophic structure refers to the different feeding relationships in an ecosystem which, in turn, determine the route of energy flow and the pattern of chemical cycling.

An overview of energy and nutrient dynamics in an ecosystem

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Food chains have been used to explain the transfer of energy from the sun (the ultimate source of energy) to producers and consumers.

Sample Terrestrial and Marine Food Chains

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Food chains are more accurately in nature linked together in food webs. Trophic relationships in a community are dependent on who eats whom. Depending on the organism’s diet it could be a primary consumer, secondary consumer, or tertiary consumer.

A stable community is like a pyramid with interactions among the levels shown in the pyramid below. These interactions are often beneficial to organism, but detrimental to another. The struggle for survival of the various levels within the community determines the structure of the community.

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There are two different hypotheses to explain the limits that exist on the length of the food chain. First, the energetic hypothesis states that about 10% of the energy stored in each trophic level will be converted to organic matter in the next trophic level. Ultimately, this is not a very efficient transfer of energy. Second, the dynamic stability hypothesis suggests that long food chains are less stable than short food chains, therefore, any population fluctuation at a lower trophic level will be magnified at a higher trophic level.

II. Counting Beans – Ecological Sampling Techniques

Ecological sampling techniques are used because it is often difficult to count every organism in a particular location. Ecologists use the information obtained by these techniques to monitor population density which is an indication of species health. Random sampling techniques are used because they help ensure that the samples are representative of the whole population.

The type of organism being sampled will determine the most useful techniques. Plants and non-motile animals are often sampled by quadrats or transects. Aerial observations work well for large animals found in areas with few trees. Mobile animals, both large and small, are often sampled with a mark-recapture technique. Mark-recapture involves catching the species of interest and marking them with a band, paint spot, notch, or photograph. The animal is then released close to its spot of capture. After the animal has had time to be reintegrated into the population, the ecologist will collect a second sampling of the animal. Counting how many of the marked animals are recaptured during the second collection can be used to estimate population size. This method is known as the Lincoln-Peterson Index. The formula is:

                N = M · S      where         N = population size estimate

                                  R                      M = marked individuals released (from first capture)

                                                          S = total size of the second sample

                                         R = marked individuals recaptured on the second sample

Things to remember about the Lincoln-Peterson model:

• While this is not a closed population, there is not a significant effect on the population numbers due to birth, death, immigration, and emigration.
• Everyone has an equal probability of being caught a second time. While survival is never guaranteed; marking, releasing, and recapturing should not threaten the animal’s ability to survive.
• There are enough animals recaptured to accurately estimate the population size.

Objectives

• To imitate a small food chain in order to demonstrate how they work.

• To gain an understanding of trophic level interactions and energy transfer
• To understand the importance of ecological sampling
• To learn a variety of ecological sampling techniques
• To simulate a mark-recapture method of sampling and use the data to estimate population size

Materials

• Laboratory resource
• Game pieces
• Lab notebook and pen
• Container for holding beans
• 500 dried beans (can be kidney or pinto beans)
• 1/4 measuring cup
• Black marking pen
• Medicine counting tray
• Calculator

Procedure

I. Food Web Game – Take My Energy, Maybe?

1. Game pieces included in the game and their trophic level:

        Sunflowers (10) – producers

        Mice (5) – primary consumer

        Snakes (3) – secondary consumer

        Cougar (1) – tertiary consumer

        Raccoon (1) – omnivore who feeds at multiple levels

1. Draw one of the game pieces to determine your role in the food chain. DO NOT TELL ANYONE which organism you have drawn.
2. You will be given a number of energy points to start with depending on which organism you have drawn. If you are eaten during the game, you will give up points as indicated on the game piece to whatever ate you. If you are the one who eats what you encounter, then you will gain points as indicated on the game piece. If you come in contact with an organism not on your diet, then you will lose points having to deal with that organism.
3. There will be four rounds of the game. Sunflowers will acquire 1 energy unit each from photosynthesis at the beginning of each round; this will be added at the final tally of energy points. When each round begins, walk around until your instructor says FEED!  At this time, find one person close to you. You will quietly show each other your game piece. There will be music playing in the background to help hide any quiet discussion that may happen. If the other person shows you their game piece and they are a prey organism, take the appropriate number of energy points. If the other person turns out to be a predator, you will need to give them points because you were eaten. Remember, you want to be discrete about sharing information.
4. Record your points gained or lost for each round on the small index card provided (round 1, +2; round 2, -1, etc.). After four rounds, as a class, we will add up all of the energy units for each round and record in the chart provided. At the very end, you will subtract 8 points for each organism (3 for each sunflower) as heat lost to the environment. We will be able to see how much energy is left over at the end.

II. Counting Beans – Ecological Sampling Technique

1. Use the medicine counting tray to count out 500 of the dried beans provided.
2. Place the beans in a container.
3. Use the ¼ measuring cup to obtain a sample of beans.
4. Mark both sides of the beans in the measuring cup and return them to the container. Place the lid on top.
5. Gently shake the container to thoroughly mix the contents.
6. Obtain a second sample of beans with the ¼ measuring cup.
7. Count the number of marked and unmarked beans in the measuring cup. Record this information where indicated on the worksheet.
8. Using the formula provided, calculate the Lincoln-Peterson index for estimating population size.

Results

Complete the worksheet. The textbook and Internet resources may be utilized to identify organisms and answer the questions. You may work in groups of 2 (work with another group for yeast budding) however, your answers must be in your own words. All references used should be presented in APA format at the end of the worksheet.