1 Primary Consumer Energy Flow Investigation Objectives Observe the life cycle of the painted lady butterfly (Vanessa cardui). Construct a trophic diagram depicting a typical North American food chain Measure the efficiency of energy transfer from one trophic level to another. Energy moving through an ecosystem originates in the sun. Solar radiation is responsible for all primary productivity. Energy that is stored in a primary producer biomass is transferred to a primary consumer, or herbivore, biomass when the herbivore consumes and digests the primary producer biomass. The energy captured in the herbivore biomass is then transferred to a primary carnivore when the primary carnivore consumes the herbivore. The chain continues as energy is transferred from primary carnivores to secondary carnivores and so forth. At each these levels of the food chain, referred to as trophic levels, much of the energy transferred from one trophic level to the next is lost for many reasons. One is the fact that not all of the biomass at one level is consumed by organisms of the next higher level. Of the biomass that is consumed, not all is digested and turned into biomass at the next level. Some becomes waste in the form of feces or frass. Also, processes such as cellular respiration require energy and thus transform some of the chemical energy of the biomass into heat. The efficiency of energy transfer varies greatly from one food chain to the next and is extremely dependent on environmental factors such as temperature, aquatic vs. terrestrial habitats, complexity of food web, etc. Generally, about 10% of the energy at one trophic level is transferred to the sent, but efficiencies range anywhere from less that 1% to 25% or higher. Background Prelab 1. What is the primary source of energy for most terrestrial ecosystems? 2. Describe what a primary producer (autotroph) is and give two specific examples of organisms that are primary producers. 3. Describe what a primary consumer (herbivore) is and give two examples of primary consumers. 4. Why isn't all energy transferred to subsequent trophic levels? List as many reasons as you can.
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Primary Consumer Energy Flow
InvestigationObjectives
Observe the life cycle of the painted lady butterfly (Vanessa cardui).
Construct a trophic diagram depicting a typical North American food chain
Measure the efficiency of energy transfer from one trophic level to another.
Energy moving through an ecosystem originates in the sun. Solar radiation is responsible for all primary productivity. Energy that is stored in a primary producer biomass is transferred to a primary consumer, or herbivore, biomass when the herbivore consumes and digests the primary producer biomass. The energy captured in the herbivore biomass is then transferred to a primary carnivore when the primary carnivore consumes the herbivore. The chain continues as energy is transferred from primary carnivores to secondary carnivores and so forth.
At each these levels of the food chain, referred to as trophic levels, much of the energy transferred from one trophic level to the next is lost for many reasons. One is the fact that not all of the biomass at one level is consumed by organisms of the next higher level. Of the biomass that is consumed, not all is digested and turned into biomass at the next level. Some becomes waste in the form of feces or frass. Also, processes such as cellular respiration require energy and thus transform some of the chemical energy of the biomass into heat.
The efficiency of energy transfer varies greatly from one food chain to the next and is extremely dependent on environmental factors such as temperature, aquatic vs. terrestrial habitats, complexity of food web, etc. Generally, about 10% of the energy at one trophic level is transferred to the sent, but efficiencies range anywhere from less that 1% to 25% or higher.
Background
Prelab 1. What is the primary source of energy for most terrestrial ecosystems?
2. Describe what a primary producer (autotroph) is and give two specific examples of organisms that are primaryproducers.
3. Describe what a primary consumer (herbivore) is and give two examples of primary consumers.
4. Why isn't all energy transferred to subsequent trophic levels? List as many reasons as you can.
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ProcedureSet-up: Preparing Culture Cups for Larvae1. Thoroughly wash your hands before handling the materials to set up your culture cups.2. Obtain two culture cups with lids and two pieces of tissue paper. Create 15 holes on each lid using a push pin.3. Place a paper towel over each cup. Use scissors to cut a circle 1.5 cm wider than the lid. Snap the lids into place on thecups, securing the tissue paper on the opening of the cup.4. Measure the mass of the empty Control Cup, the cap, and the paper towel with a balance. Record the Mass EmptyCulture Cup for the Control Cup in Table 1.5. Using a wooden spatula and a ruler, scoop and pack 1.5 cm of food medium (to the marked fill line) into the bottom ofthe cup, making sure the medium’s surface is smooth and even.6. Return the culture cup with food to the balance and record the Mass Culture Cup with Food (including lid and tissuepaper) for the Control Cup in Table 1.7. Calculate the Mass of Food by subtracting the Mass of Empty Culture Cup from the Mass of Culture Cup with Food andrecord this value for the Control Cup in Table 1.8. Repeat the previous four steps for the larvae cup and record each measurement in Table 1.9. With a sorting brush, gently brush two butterfly larvae into the cup labeled “Larvae.”10. Replace the lids on both cups, securing the tissue paper in the seal between the rim of the cup and the lid.11. Measure the mass of each cup and record the figures along with today’s date in Table 2.
1. Measure and record the masses of both the control cup and larvae cups along with any observations about theexperiment at the same time every day until three days after the butterfly larvae attach to the tissue paper at the top ofthe culture cup and have formed their chrysalis. Record your data from each day in Table 2.
2. If there are any days (i.e. weekends) where you do not have access to your experiment, simply divide the mass lossover the time period and assume a consistent loss of mass occurred each day during that time. For example, if youare unable to measure the cups on a Saturday and Sunday, do the following:
a. Record the mass on Monday.b. Subtract Monday’s measurement from Friday’s measurement.c. Divide the difference by 3.d. Subtract the quotient from Friday’s measurement, then record the difference as Saturday’s mass
measurement.e. Subtract the quotient from Saturday’s measurement, then record the difference as Sunday’s mass
measurement.3. If you notice that the tissue paper has disintegrated, complete the following steps to replace it:
a. Obtain a new piece of tissue paper from you teacher.b. Using a balance, measure the mass of the tissue paper and record it in your notes.c. Carefully open your larvae cup and place the tissue paper over the opening, leaving the original tissue paper
in place.d. Carefully replace the lid and record the mass of the cup with the new tissue paper. Subtract the mass of the
tissue paper from the total mass and record this for today’s measurement.NOTE: You will have to subtract out the mass of the extra tissue paper from the total mass for each day forthe remainder of your experiment.
Collecting data throughout the experiment
Data Collection
Table 1. Set-up (day 1)
Control Cup Larvae Cup
Cup Number:
Mass of Culture Cup with Food (including lid & tissue paper) (g):
Mass of Empty Culture Cup (including lid & tissue paper) (g):
Original Mass of Food (g):
(Mass of Culture Cup w/ food - Mass of Empty Culture Cup)
Table 2. Daily Mass Measurements (day 2-?)
Date Mass of Control Cup (g) Mass of Larvae Cup (g) Observations
Table 3. Final Data
Control Cup Larvae Cup
Final Mass of Chrysalises (g):
Mass of Leftover Food (including cup, lid & tissue paper) (g):
Mass of Empty Culture Cup (including lid & tissue paper) (g):
Final Mass of Leftover Food(g):
(Mass of Leftover Food - Mass of Empty Culture Cup)
Lid mass_________ Paper towel mass: _____________ Cup (without lid) mass: _______________
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Analysis of Results - Calculations
Table 4. Mass Loss of Culture Cups
Control Cup Larvae Cup
Date Daily Mass
Loss (g)
Cumulative
Mass Loss (g)
Daily Mass
Loss (g)
Cumulative
Mass Loss (g)
Larvae Daily Mass Loss – Control Daily
Mass Loss (g)
4/20 N/A N/A N/A N/A N/A
Table 5. Percent Efficiency
Larvae Cup
Final Mass of Chrysalises (g):
(from Table 3)
Mass of Food Consumed (g):
(Original Mass of Food – Final Mass of Leftover Food)
% Efficiency:
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Analysis of Results – Discussion Questions
1. What is the purpose of having a control in this experiment?
2. Why was the mass loss of the control subtracted from the mass loss of the cups with butterfly larvae?
3. Describe the significance of the two plots in the graph titled Cumulative Mass Loss of Culture Cups.
4. Describe the general shape of the plot on the graph titled Larvae Daily Mass Loss Subtracting the Control Daily
Mass Loss. Why is the curve shaped like that?
5. Why was there a greater mass loss in the culture cups with larvae than in the control cup with no larvae?
6. The painted lady butterfly can be part of the following food chain that is typically found in North America (mass
of representative organisms follows in parentheses): mallow leaves (butterfly food medium constituent) (0.2 g
per leaf), painted lady butterfly (0.5 g), American robin (77 g), domestic house cat (5,000 g). Assuming that 10%
of the biomass from one trophic level is transferred to the next trophic level, calculate the number of robins,
caterpillars, and mallow leaves that must be consumed to support one 5,000 g domestic house cat in this food
chain.
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7. Construct a biomass pyramid diagram depicting the food chain described in the previous question.
8. What was the experimental efficiency of biomass transfer in this experiment? Is this significantly close to the
hypothetical efficiency delineated by the “ecological rule of thumb?” Explain why or why not.
9. Why do you think there are rarely food chains with more than four trophic levels?
10. Describe any occurrences in this experiment that may have led to skewed results.
Conclusion – Write a 2-3 sentence conclusion summarizing the purpose of the lab, your results and possible sources of
experimental error.
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Final Data Collection
1. On the fourth day that the larvae are in the chrysalis stage, carefully, so as not to disturb the chrysalis, remove the
lid of the cup. Gently remove the tissue paper to which the chrysalises are attached. Using a pair of forceps,
grasp each chrysalis by the small point of attachment to the tissue paper and pluck it from its attachment point.
Repeat this procedure for the second chrysalis.
2. Place both chrysalises on the balance. Measure and record on the data sheet the combined mass of both
chrysalises.
NOTE: If the fourth day falls on a day when you will not have access to the larvae, complete this step on your last
day of access prior to the fourth day.
3. Conditional Action: If the caterpillars have not consumed all of the food medium in the cups, and there is
significant amount of medium left in the bottom of the cup (i.e., food medium entirely covers the bottom of the
cup):
a. Use forceps to remove as much frass, silk and shed exoskeleton, etc. from the cup as possible. Be careful
not to confuse frass with food. The two substances are the same color, but frass will appear as tiny
pellets, and food media will be in its original configuration and location at the bottom of the cup.
b. Find the mass of the leftover food and record this value in Table 3.
c. Calculate the Final Mass of Leftover Food by subtracting the Mass of Empty Culture Cup (from Table 1) from
the Mass of Leftover Food (including cup, lid & tissue paper). Record this value in Table 3.
Table 5. Percent Efficiency
Larvae Cup
Final Mass of Chrysalises (g):
(from Table 3)
Mass of Food Consumed (g):
(Original Mass of Food – Final Mass of Leftover Food)
% Efficiency:
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