PROCEDURE:
HANDS-ON
ACTIVITY: Components of a food web
Objective: Students explore the roles of plants/algae/producers,
herbivores, predators, and decomposers/detritovores, in aquatic food
webs through observation, guided discussions, and written exercises.
Students define how each type of organism acquires energy and nutrients,
and can identify the category in which an organism belongs.
Method: Students divide into four groups of ~5 people. Each group
sits in a circle surrounding a tank or tanks containing representative
of one food web component:
Producers: Algae, macrophytes, aquatic plants.
Herbivores: Snails, Heptageniid mayflies, weevils, leaf beetles,
catfish/plecostomus, tadpoles.
Predators: Predatory stonefly, diving beetles, dragonflies, damselflies,
minnows, salamander larvae/newts.
Decomposers: Baetids, shredding stoneflies, watermold (under microscope)
Each group observes their tanks. Students draw pictures of one or
more organism, and discuss the questions below.
Producers:
Plants and algae use photosynthesis to convert sunlight into energy
in the form of sugar.
• Other than light, what else do plants and algae need
to grow?
• If your tank has been sitting in a sunny spot, you
may see many small bubbles in the water. What are these bubbles made
of, and how did they appear? Hint: What does photosynthesis produce
besides sugar?
• Plants and algae have a large variety of shapes and
growth patterns; for example, some float in the water or on the surface,
while others are attached to rocks. Describe in words some of the
different shapes you see and discuss why this shape helps the plant
conduct photosynthesis. Think about the different types of habitats
these plants occur in, like ponds and lakes versus streams and rivers.
Herbivores:
Herbivores obtain energy by eating plants and algae.
• How can you tell if an animal is an herbivore by examining
its structure? What features of these animals tell you that they
are herbivores?
• Where would you expect to see more herbivores: a pond
in a forest, or in a field? Why?
• If you weighed all the plants and algae in a pond,
and all the herbivores, which would weigh more? Why?
Predators:
Predators obtain energy by eating other animals.
• How can you tell if an animal is a predator? What structural
features do you see in these animals that indicates they are predators?
• Predators can eat not just herbivores, but decomposers
and other predators as well. How does this flexibility in diet affect
the food web?
• Predators are typically the least numerous organisms
found in a pond or stream. Why?
Decomposers:
Decomposers eat dead organic matter, or detritus from plant or animal
sources.
• Name as many sources of organic matter (detritus) in
a pond you can think of in a minute. Where do they come from? Do
they all originate from within the pond?
• Structurally, decomposers are probably the most diverse
group of organisms in the food web. Why? Hint: Look over some of
your answer to question 1.
• Many stream insects, like stoneflies, eat fallen leaves
that fame from trees growing nearby. How does this diet make stoneflies
similar to herbivores in terms of their location on the food web?
How are they different?
Options:
• Each group is assigned one food-web component. After
analyzing the questions, the group presents their discoveries about
that component to the rest of the class.
• Each group sits at one station, which has tanks representing
each component. Students may divide questions up amongst themselves,
or answer all of them as a group.
Students rotate between stations, which have tanks representing
only one component.
FOOD WEB YARN ACTIVITY:
Play the food web game by passing out the assigned organism nametags.
Start with the designated first organism (sun), have the student
read their description of what they are and have them figure out
what organism they are linked to in the circle and how they are related
to that other organism. Have them hold onto their piece of string
and then through that attached ball of string to the next organism
in the circle and so on.
PROCEDURE:
Assign each student an organism and have them write out a piece
of paper describing what they are and what they eat, are eaten by,
or do; also make a nametag with just their organism's name on it
.
Go outside or clear a large space in the classroom and have the
students make a fairly large circle (the larger the circle, the easier
it is to represent a web pattern) .
Give the ball of string to the designated first organism and have
them say what they are and what they eat, are eaten by, or do to
direct towards the next step of the game .
Once the web is created, show what happens when an organism is removed
from the web. Have that student drop their segment of string to represent
that the web's tightly woven structure will be loosened. Discuss
the interconnected destruction that occurs.
Point out the terms producer, herbivore, omnivore, carnivore, and
decomposer using examples from the game .
Discuss the concept of predator eating prey and the importance of
prey and predator being present in the food web (control of populations
and importance of nourishing themselves and young).
Example question: If a rabbit was removed from our game's food web,
how are two other of our game's organisms affected?
Example answer: The coyote wouldn't have enough food to eat and,
due to the loss of its "predator," the rabbit's favorite
type of grass would not have a control on its population.
|
