Download Lab 2 Food Chains, Food Webs, and Ecosystems

Lab 2 Food Chains, Food Webs, and Ecosystems
Objectives:
1. Define food chains.
2. Distinguish between food chains and food webs.
3. Understand trophic levels.
4. Understand how trophic levels apply to organisms.
5. Understand the major pathways of energy flow and matter cycles in
ecosystems.
Introduction:
Food chains are a series of organism that eat each other. They help us visualize how
energy flows through ecosystems. Food webs are a complex network of many
interconnected food chains and feeding relationships. Remember these are simple
representations and true ecosystems are very complex.
Ecosystems:
An ecosystem is a group of organisms and their physical environment, all interacting
by a flow of energy and a cycling of nutrients. There are two key concepts that you
should understand in relation to ecosystems.
1. Energy flows through an ecosystem.
This flow occurs in one direction only; the flow generally starts with light and
heat energy from the sun. It generally ends as the metabolic heat given off by
organisms in an unusable form into environment. Remember that all living
organisms respire, and during this process they use energy. Only the energy
organisms are able to store can be passed to the next level.
2. Matter cycles in an ecosystem
This cycling of material is very important. It is how chemicals like carbon,
nitrogen, and phosphorus move from organism to organism in an ecosystem.
In general energy flows and matter cycles are closely tied together. For instance, when
an owl eats a mouse both matter (proteins, carbohydrates, and fats) and energy
(stored within chemical bonds) are transferred from the mouse to the owl.
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In ecosystems there are three groups that make any functional ecosystem. These are:
Producers, Consumers, and Decomposers. They can be linked together by matter
cycles and energy flows.
A general model of an ecosystem is depicted below.
General Ecosystem Model
Heat (energy lost)
Ecosystem
SUN
Producers
Energy
Consumers
Matter/Nutrients
Decomposers
Nutrient
Reservoir Pool
Drawing adapted from C. Olmsted
The first functional group is the primary producers. All of these organisms are
autotrophic, that is they can convert sunlight into useable energy via photosynthesis.
These organisms are mainly plants, but also include members of other groups like
Monera (cyanobacteria) and the Protista (kelps, Volvox, and autotrophic euglena).
These organisms form the base for any food chain or web without then there can be no
ecosystem.
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The second functional group in an ecosystem is the consumers. They feed on both
the primary produces and other consumers. These can then be further broken down
into groups of organisms based on what they eat. We term these groups’ trophic
levels. All organisms that are the same number of energy transfers away from the
original source of energy are at the same trophic level.
For example, all producers belong to the first trophic level, all herbivores (which feed
only on the primary producers) are at the second trophic level in a food chain or web.
We call herbivores the primary consumers. A carnivore or secondary consumer
then eats the primary consumer. This process can continue for several steps. While
we generally put an organism in a specific trophic level most of them truly feed on more
than one trophic level. For instance, bears are omnivores (eating both plants and
animals) and can feed a primary consumer level when eating plants, a secondary
consumer level when eating deer, or even at higher levels when eating fish (large fish
are often 3 or 4level consumers).
The third functional group, which is no less important, is the decomposers. These
organisms are the keys to nutrient cycling in ecosystems. As you have seen some
decomposers are fungi and bacteria. We will also see that many other small organisms
are decomposers, these are often called detritovores (feeding on detritus). Because
all organisms create waste and eventually die they continually add to the detritus pool.
Decomposers are not generally placed into a trophic level, but are extremely important.
Remember that a large percentage of the energy and nutrient flow from
produces goes directly to the decomposers and is not available to consumers.
Procedure 1. Using the box model presented above complete Procedure 1
on the laboratory worksheet.
Food Chains and Pyramids:
We can construct simple linear representations of energy flow and matter cycles
Trophic levels break down as follows:
Producer Primary Consumer Secondary Consumer ….
Top Consumer.
Energy is lost (as usable energy in the form of heat) at each trophic level. Enough
energy is lost at each trophic level that food chains are often limited to usually 3- 4
levels or rarely 5-6 trophic levels. On average 10% of the energy is passed between
trophic levels, with the other 90% being unavailable to the other groups.
We can show this minimal energy transfer with a pyramid of biomass pyramid that
represents mainly matter.
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Or with a pyramid of energy that includes both matter and energy.
Using the following organisms construct a food chain: rabbit, wolf, grass.
How many rabbits do you think are needed to keep a wolf alive for 1 month?
How many grass plants will all these rabbits need to survive for one month?
Food Webs:
Food webs are complex networks of food chains that represent feeding relationships.
They help you understand the complexity of these relationships.
In the following activity, you will build a food web to demonstrate how complex these
systems can be.
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Procedure 2: Onto the Desert/Into the Forest:
The object of this activity is for all the members of a group to work together to form
a food web. From the deck of cards on the table (after shuffling), each member of
the group will in order turn the top card and try to place it onto the table into a food
chains that from webs. Chains can be added to at the top, bottoms and sides. Use
chalk or markers to draw lines between the cards showing which way energy is
flowing.
Complete the questions in Procedure 2 Part A that relate to the food web
your group constructed.
Now try to arrange the cards into a pyramid.
Try to show the energy flow in this pyramid.
Complete the questions in Procedure 2 Part B that relate to the food web
your group constructed.
Procedure 3: A Walk on the Mountain
Mount Tabor
This is obviously not a natural Oregon ecosystem. Describe the park, the organisms
you see, and how man has created this ecosystem. Given what you know about this
area, tell what parts of habitat are natural and what parts are put there by man or
closely regulated by man.
After finding your organisms, find a place to sit and look over the valley. Think about
what you see in ecological terms.
(Homework)Procedure 4: Thinking About Nature
Read from the class website: “There is a Hair in my Dirt’” by Gary Larson
Answer the questions in your laboratory worksheet.
From the class website the video clips and answer the questions in the packet.
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Thinking Ecologically about Organisms
While any organism can be grouped into the general categories of producer,
consumer, and decomposer, ecologically it is necessary to broaden your
perspectives about the attributes of living organisms and where they get their
energy to sustain their own needs and reproduce.
There are several questions you should address examining any
organism:
1. What does the organism feed on?
2. How does it acquire its food?
3. What are the environmental requirements needed for the organism to
survive?
4. How does the organism move?
5. How does the organism reproduce?
Terms:
Trophic level
Consumer
Herbivores
Consumption efficiency
Ecosystem
Food Chain
Omnivores
Decomposers
Primary Producer
Carnivores
Detritus
Ecological pyramid
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Lab 2 Ecosystems
Bio 101 General Biology
Name: _____________________
Date _______________
Procedure 1
The General Ecosystem Model
The organisms listed below live together in a biological community. Using the
ecosystem box model (like on page 2) show how energy flows and nutrients cycle
through this community. Start with sunlight and end with heat; try to include every
organism in your diagram. See if you can identify the trophic level of each consumer.
Label all boxes and arrows.
Grass
Ground squirrel
Chipmunk
Falcon
Pine tree
newt
Soil fungi
Mushroom
Owl
Earthworm
grasshopper
moth
tick
rabbit
lichen
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Procedure 2: Activity
Part A
Once the food web is complete, stand back and observe it. Write your observations
about the web as you are making it and upon completion. Discuss why each card was
placed as it was.
Observe the food webs made by other groups. Discuss the similarities and differences
between the different webs.
Part B
How many producers did you have? ____________________
How many primary consumers did you have? _______________
How many secondary consumers did you have? ______________
How many other levels did you have? _________________
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Do you think this represents a true ecological community? Explain your answer.
Procedure 3: A Walk on the Mountain
Mount Tabor
This is obviously not a natural Oregon ecosystem. Describe the park, the organisms
you see, and how man has created this ecosystem. Given what you know about this
area, tell what parts of habitat are natural and what parts are put there by man or
closely regulated by man.
List at least 15 organisms you see and list their trophic level (producer, primary
consumer, secondary consumer, tertiary consumer, decomposer). If you don’t know
the species of tree or plant describe it or sketch the leaf and flower if available. Field
guides are available: See your instructor.
ORGANISM
1
2
3
4
5
6
7
8
TROPHIC
LEVEL
ORGANISM
TROPHIC
LEVEL
9
10
11
12
13
14
15
16
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Describe one microhabitat. A microhabitat is a small area where abiotic characteristics
are different from those in the environment in general (i.e., temperature difference,
more or less moisture, etc). Describe how it is different. Think of all biotic and abiotic
factors that might be different.
Look for areas that might be changing. What is happening? If man does not interfere
except to water, what do you think this area would look like in 50 years?
Identify an area the you think decomposition happening, examine it closely What do
you observe?
Procedure 4. Biogeochemical Cycling-Natural Systems
What is the difference between a turtle and a tortoise?
What does Larson say about loving nature and understanding it? Explain the difference.
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Procedure 4 Biogeochemicals part 2
1. “Little things nutrient cycling” E. O Wilson
What does E.O. Wilson say would happen if the “decomposers” were to disappear from our ecosystems?
2. Oxygen-global cycling –Nova 10-minutes
Why is oxygen so important? _________________________________________
What organisms are producing oxygen? _______________________________________________
What is often described as the “lungs of planet” earth? ___________________________________
What is the extra step described in the video? _____________________________________________
Why do we now have a better understanding of the global oxygen cycle?___________________
What are really the lungs of the earth? ______________________________________________
3. Ecology (Phosphorus-global processes –Nova 11-minutes)
What covers the floor of the lakebed in the Bodele depression?
_____________________
How many square miles is does the diatomite cover? ______________
How often does the dust cloud rise? ______________________
What happens to the dust at the coast?_____________________
Where does the dust go?___________________
The exchange of nutrients is happening when and where?
_____________________________________________________________________
The earth system can best be described as ________________________.
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4. Biogeochemicals (“Nitrogen global lightening” Nova-6 minutes)
What drives the occurrence of lightning?
_______________________________________________________________________________
How many lightning bolt strike the earth every day? _______________
How many tons of nitrates do this produce? _______________________
Then where does it go? _______________________________________
What do we use nitrates for in our bodies? __________________________
5. DVD Ecology (Human Impacts-Nova- 4 minutes)
Currently human presence can be seen over _________ % of the land mass.
Humans manufacture _______________ the nitrate produced by lightning.
Industry and transportation produce more ___________ than the Amazon captures.
What is the key difference be natural cycles and human caused changes?
_____________________________________________________________________________________
What are satieties telling us?
1. ________________________________________________________________________
2. _______________________________________________________________________
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6 Nitrogen Cycling
Video Clips in Biogeochemical
Salmon-trees
Salmon 2 long
Nitrogen Forest Bear Hair- 11 minutes
Attach a one paragraph typed sheet that
describes in general terms with some associated details the answers to the following
questions.
What is the relationship between the salmon and the forest? What biogeochemical is
most responsible for this a relationship? Besides bear what other organisms are
feeding on the salmon? How is the relationship between nitrogen salmon and bear
documented? How do the hair traps help us understand these interrelationships?
Attach a sheet with typed answers to the following questions.
Summary Questions:
1. Can an organism occupy more than one trophic level? Explain, giving examples,
why or why not?
2. What might happen if a single species was removed from a food web?
3. What may happen to toxins that enter the food web at a low trophic level?
Why might this happen?
4. Why is decomposition so important? What would happen if nature was not
efficient at this process?
5. Why are food chains rarely more than 4 links long?
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