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Exercise 17
odonate, Tetragoneuria spp.) under different conditions of light and prey densities.
The prey will be Daphnia magna, a relatively large zooplanktonic cladoceran.
Effects of Light on Predator Success
Procedures
1. Place one bluegill and one odonate into separate containers filled with equal
volumes of water at room temperature. Allow the organisms to acclimate for
15 min without disturbance (such as loud noise or startling moves), particularly
around the fish. These predators have been starved and should feed readily.
2. Select 30 Daphnia of similar size from the available culture. Carefully add 15
Daphnia, one at a time with a wide-bore pipet, to each container and observe the
feeding for 3 min. Remove the predators and count the prey remaining in each
container. Record the number of prey consumed by each predator. Place each fed
predator in a designated repository to avoid accidental reuse in subsequent
experiments.
3. Repeat steps 1 and 2 above, but place the containers into total darkness immediately
after adding the prey to each. Speed is essential when adding prey and placing
the containers into darkness and when removing the predators after the 3-min
feeding period.
Questions
1. Based on your observations and pooled class data on the feeding in light, compare
predation by the fish and by the odonate.
a. How does each predator detect prey?
b. How does the prey organism detect the predator? What defenses does the prey
appear to have?
c. What predation strategy (searching or ambushing) is employed by each predator?
d. What energy considerations are associated with each strategy?
e. How are the prey consumed by each predator, and how does this affect feeding?
f. What additional information would be useful in making a more complete
evaluation of the effects of light on these predators?
g. What environmental (habitat) factors favor each predator?
h. What sources of error are possible in these experiments? How would they affect
the results?
2. Why should exotic predators or prey not be introduced into natural ecosystems
without "considerable forethought"?
The Effect of Prey Density on Predator Success, A Functional Response
Procedures
1. Place one bluegill into each of three containers and an odonate in each of three
additional containers. The containers should be filled with an equal volume (same
as in the above) of water at room temperature before adding the predators.
2. Select 320 Daphnia of similar size from the available culture. Separate these prey
organisms into two sets of 30 prey, two sets of 50 prey, and two sets of 80 prey.
3. Pair the six containers with predators such that each of the three pairs has a fish
and an odonate. Add 30 prey to each container of one pair, 50 to each container
of another pair, and 80 to each container of the third pair. All trials should not
Exercise 17
odonate, Tetragoneuria spp.) under different conditions of light and prey densities.
The prey will be Daphnia magna, a relatively large zooplanktonic cladoceran.
Effects of Light on Predator Success
Procedures
1. Place one bluegill and one odonate into separate containers filled with equal
volumes of water at room temperature. Allow the organisms to acclimate for
15 min without disturbance (such as loud noise or startling moves), particularly
around the fish. These predators have been starved and should feed readily.
2. Select 30 Daphnia of similar size from the available culture. Carefully add 15
Daphnia, one at a time with a wide-bore pipet, to each container and observe the
feeding for 3 min. Remove the predators and count the prey remaining in each
container. Record the number of prey consumed by each predator. Place each fed
predator in a designated repository to avoid accidental reuse in subsequent
experiments.
3. Repeat steps 1 and 2 above, but place the containers into total darkness immediately
after adding the prey to each. Speed is essential when adding prey and placing
the containers into darkness and when removing the predators after the 3-min
feeding period.
Questions
1. Based on your observations and pooled class data on the feeding in light, compare
predation by the fish and by the odonate.
a. How does each predator detect prey?
b. How does the prey organism detect the predator? What defenses does the prey
appear to have?
c. What predation strategy (searching or ambushing) is employed by each predator?
d. What energy considerations are associated with each strategy?
e. How are the prey consumed by each predator, and how does this affect feeding?
f. What additional information would be useful in making a more complete
evaluation of the effects of light on these predators?
g. What environmental (habitat) factors favor each predator?
h. What sources of error are possible in these experiments? How would they affect
the results?
2. Why should exotic predators or prey not be introduced into natural ecosystems
without "considerable forethought"?
The Effect of Prey Density on Predator Success, A Functional Response
Procedures
1. Place one bluegill into each of three containers and an odonate in each of three
additional containers. The containers should be filled with an equal volume (same
as in the above) of water at room temperature before adding the predators.
2. Select 320 Daphnia of similar size from the available culture. Separate these prey
organisms into two sets of 30 prey, two sets of 50 prey, and two sets of 80 prey.
3. Pair the six containers with predators such that each of the three pairs has a fish
and an odonate. Add 30 prey to each container of one pair, 50 to each container
of another pair, and 80 to each container of the third pair. All trials should not