What Can We Learn About Interdependence at the Pond?

• Lesson A - Should We Introduce Mosquitofish into the Habitat Area Pond?
• Lesson B - Reptiles and Amphibians

Lesson A - Should We Introduce Mosquitofish into the Habitat Area Pond?

FYI

Each of the biotic members of the habitat area pond community has a role to play in that habitat. This role is called a niche. How a species interacts with other organisms, what it eats, and the methods it uses to obtain food all help define its niche.

This lesson focuses on the methods used by pond organisms to obtain food or nutrients. In a healthy pond community, we expect to find organisms filling the roles of producers (plants), primary consumers (herbivores), secondary consumers (predators), and decomposers (scavengers). Omnivores are animals that eat both plants and animals. (Humans are omnivores.)

Mosquitofish are predators; their primary food is mosquito larvae. Other animals or aquatic invertebrates in the aquatic habitat also may eat mosquito larvae. Mosquitofish are introduced into ponds or areas of standing water by local vector control agencies to reduce mosquito populations. So far, Oregon has been relatively free of mosquito-borne illness that causes serious harm to humans.

But, mosquitos have become more of a threat to human health in other parts of the U.S., and that trend could spread to Oregon, too.

In order to answer the Natural Resource Management Question “Should we introduce mosquitofish into the habitat area pond?,” learners must determine which organisms are filling the roles of producers, primary consumers, secondary consumers, and scavengers.

They then must decide whether there is room (biotic energy) within this community for an additional predator, or whether they are willing to accept the loss of other organisms to attain the perceived benefits of limiting the mosquito population.

Do not introduce live mosquitofish into a habitat area pond that has any connection to a natural body of water.

MATERIALS

Part 1

• Quick Reference Guide to Aquatic Invertebrates cards (PDF - 4,340KB), one set per team
• Worksheet Who’s on the Menu? (PDF - 30KB), one copy per team

Part 2

• Mini-aquaria, one (or more, if a control is needed) per team for each experiment
• A large aquarium (or two, if you keep the mosquitofish separate)
• Elodea purchased from a pet store, and/or natural pond weeds and algae
• Sticks, rotting plant materials, or detritus collected off the pond bottom
• Dead leaves with some algae on them (they feel slimy)
• Mosquitofish (Gambusia) purchased from a biological supply company
• Aquatic macro-invertebrates collected from the pond

PREPARATION

Leaders should review the following:

• FYI section
• 4-H Science Inquiry Model
• Learner evaluation criteria in the ODE Scientific Inquiry Scoring Guide (PDF) to assist in coaching learners
• Photocopy sets of Quick Reference Guide to Aquatic Invertebrates cards onto card stock (if you do not already have enough sets from previous lessons).

PROCEDURE

Part 1

Pass out a set of Quick Reference Guide to Aquatic Invertebrates cards and a copy of worksheet Who’s on the Menu? to each team. Ask learners to look at the “How I Get Food” section of the cards. Sort them into the categories Herbivores, Predators, Scavengers, and Omnivores.

Fill in the names of the aquatic invertebrates in each category
on the worksheet. Ask learners to put an asterisk or star by invertebrates that appear in more than one category.

Remind learners of the role of plants as primary producers. Refer to Units 1 and 3 for information on how plants produce biotic energy in an ecosystem.

How many animals are both Scavengers and Omnivores? Ask learners how these two roles may be associated in the habitat. Which of the aquatic invertebrates eat the same food as mosquitofish?

(If learners have not done Lesson B—What’s in a Stream? yet, this is a good time in the lesson sequence to do it.) Have learners draw a web of life depicting their habitat pond community. Which aquatic invertebrates have they found in the habitat area pond in other lessons? What role does each play? Add mosquitofish to the web (they are predators). Add mosquito larvae, if they are not included already (they are scavengers that eat bacteria and plankton). Add algae (it contains chlorophyll and is a producer).

Part 2

Lead a discussion with learners on the roles of scavengers, omnivores, herbivores, and predators in the pond community. Ask them what else they would like to know about the habitat-area pond community to decide whether mosquitofish should be introduced.

Provide a large aquarium with a variety of organisms collected from the habitat area pond. Ask the learners to spend a few days observing them periodically. You may choose to have mosquitofish in the aquarium or in a separate aquarium. Ask learners to record any questions they have about the organisms and their behavior. At the end of this observation period, ask learners to share their questions and observations.

Working in teams, ask learners what roles and interrelationships they can test using mini-aquaria. More than one aquarium may be needed by each team. For example, a team might need two aquaria to test a question such as, “Does the presence of aquatic plants provide shelter which helps invertebrates avoid predators?” This requires two aquaria with only one different variable between them: the aquatic plants.

Possible questions learners may investigate include the following:

• Do large predatory aquatic insects, such as dragonfly larvae, eat small fish?
• Do prey (scavengers, herbivores, and omnivores) hide in plant material to avoid predators?
• How long does it take for X number of scavengers to clean up Y?
• How many mosquitofish are needed to control mosquito larva in a given space?
• Which invertebrates eat mosquito larvae?
• Do mosquitofish eat anything else besides mosquito larvae?

Ask the teams to select a question and agree on their experiment design, including a materials list and a data sheet. Follow the steps outlined in the 4-H Science Inquiry Model. Ask learners to set a time frame for the experiment; or, set one for them. Avoid openended time frames. When all the teams have completed their experiment design, ask them to share them aloud with the group. Allow learners to ask the teams questions about their design.

Pass out the materials requested by each team and facilitate, as needed, while they set up their experiments. Set the experiments aside. Allow time each day of the experiment period for learners to view the aquaria and record what they observe.

At the end of the experiment period, ask the teams to analyze and interpret the data they collect and give a summary report to the group. Working together, with all the information gathered to date, are learners ready to answer the Natural Resource Management Question? Why or why not? What else do they want or need to know? Ask learners, “How does what we learned apply to adding mosquitofish to a natural pond?” “How does this apply to introducing any animal into an ecosystem where it has not recently been found naturally?”

EXTEND THE LEARNING

A Palette of Fun (4-H 713L): Books tell a story

Project WILD Aquatic Education Activity Guide: Water we eating?

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