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Ecology Intro and Food Webs
[The goal of this lesson is to learn how energy flows through organisms in an
ecosystem, and to recognize the original source of that energy (the sun)]
Full class:
The theme for this quarter is Ecology!
What is ecology? (many answers, eventually redirect to the broad definition below)
Ecology is a branch of Biology that studies the interactions of organisms with their
environment.
What do we mean when we say "their environment"? (many answers, encourage
discussion)
Not just physical ("abiotic") factors like the weather, but also other plants and
animals. Predator species and prey species are a part of each other's environment,
so are other members of the same species ("conspecifics").
Food webs
Today we will begin exploring the field of ecology by thinking about how
organisms get their energy.
How do you get energy? (from food)
Where does that food come from? (accept lots of answers: food, other plants and
animals). If necessary: where do other animals get their energy (eventually it can be
traced back to plants).
[Reiterate that all food sources flowing through ecosystems originally comes from
plants]
If all food originates with plants, where to plants get the energy?
(The sun!)
Plants are called "Autotrophs."
Auto is Greek for "self"
Troph- is Greek for "nourishment" which means food.
A food web is a way to picture how different plants, animals, and fungi receive their
food.
Food web project:
We will provide symbols of variety of organisms to choose from. Your task is to cut
them out and arrange them to represent a realistic food web. In 20 minutes we will
meet as a big group again for the next project.
In small groups:
So autotroph means self-feeding, because plants can produce their own food from
sunlight. What are other terms for organisms in food webs?
Other key terms:
Herbivore
Predator
Decomposer
Herbivores and predators are called "consumers" and plants are called "producers."
Trophic levels
Questions in small groups after the students have completed their food webs
[Encourage the students to think about the consequences of perturbing different
parts of their food web-- e.g. what happens if a species goes extinct]
Do multiple herbivore species ever consume the same plants as food?
What would happen to the abundance (number of individuals) of one of these
herbivore species if the other one goes extinct?
Would you expect there to be a greater biomass of predators or prey species in an
ecosystem? Explain. (define biomass-- literally the mass of organisms in that
category).
Do humans ever change the food web? How? [encourage discussion]
Is all energy transferred between trophic levels, or is some energy lost? Is 100% of
energy transferred from plants to herbivores also transferred from those herbivores
to predators (No, in general approximately 10% is transferred)
Why not?
(Organisms use that energy to survive, move, and stay warm. We can feel that
energy as heat. In fact, calories are actually a measurement describing heat!)
What would happen to the abundance of herbivores if predators go extinct?
How would this change in herbivore abundance affect the plant species it
consumes?