1 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.
Transcript
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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
SUN
Producers
Decomposers
Consumers
Nutrient
Reservoir Pool
Energy
Matter/Nutrients
Heat (energy lost)Ecosystem
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?
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 Falcon Soil fungi Earthworm tick Ground squirrel Pine tree Mushroom grasshopper rabbit Chipmunk newt Owl moth 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 TROPHIC LEVEL
ORGANISM TROPHIC LEVEL
1 9
2 10
3 11
4 12
5 13
6 14
7 15
8 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? ______________________________________________
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?
