Download 1 Lab 6: Species interactions - Predation I. Introduction to Predation

Lab 6: Species interactions - Predation
I. Introduction to Predation
Predation refers to the interaction between two organisms, in which one (the prey) is killed and
consumed by another (the predator).
These interactions may occur between two organisms
belonging to different species, or between two individuals of the same species. Dynamic models of
predator-prey interactions have been developed which show how the population sizes of both
predator and prey species fluctuate over time. Past research has revealed that predation rates and
patterns of population fluctuation vary considerable in frequency and intensity in response to a
number of key factors. Primary among these factors are:
•
Relative abundances of predators and prey
•
Relative sizes of predators and prey
•
Predator gender
•
Prey physical/behavioral attributes (e.g., cryptic color, escape mechanisms)
•
Energetic quality of prey
•
Predator condition or gut fullness
•
Predator experience
•
Habitat heterogeneity
Since we can control some of the above factors in the laboratory, we can perform predation
experiments in which we measure their impact on predation rates.
II. Objectives
In this lab, we will investigate the predator-prey interaction between Gambusia holbrooki (mosquito
fish) and Artemia sp. (brine shrimp). We will vary (i) habitat conditions and (ii) predator sizes in
order to determine the influence of these two factors on predation rates.
The objectives are:
1) To demonstrate how habitat heterogeneity affects predation rates by observing predation rates of
Gambusia holbrooki on Artemia sp. under two different environmental conditions.
2) To demonstrate how predator size affects predation rates by observing predation rates of
Gambusia holbrooki on Artemia sp. using predators of two different sizes (large and small).
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III. Instructions
The predator organism for this experiment is the mosquito fish (Gambusia holbrooki), several of
which have been collected from different aquatic habitats on campus. The prey organism is brine
shrimp (Artemia sp.), several of which have been raised in the lab. The mosquito fish have not been
fed for 24 hours to improve the likelihood that they will actively forage for the prey in our
experiments.
Before you start the lab exercise, be sure to do the following:
1. Generate several hypotheses as a class that you can test with today’s exercise (Hint: the
objectives, above, may help with this).
2. Discuss how to keep track of the data that you record at your field site and set up data sheets.
3. Gather all the equipment that you will need for the lab exercise(s):
• Large Mosquito fish
• Small Mosquito fish
• Brine shrimp
• 6 1000ml Beakers
• Material for adding habitat heterogeneity to beakers
• Timer
• “USED” aquarium
Experiment 1 – Effect of habitat heterogeneity on predation rates
1) You will be provided with six 1000ml beakers, each with 800ml of aerated fresh water.
2) Label three of the beakers “HOMOGENOUS” and the other three “HETEROGENOUS”
3) In the “HETEROGENOUS” beakers place three rocks.
Leave the “HOMOGENOUS”
beakers without rocks.
4) Next you will need to add the fish to the beakers. In each beaker you will add 1 large fish.
To do this, you will use a fish net to capture a fish from the holding tank and then GENTLY
place it in the beaker.
It will then be left for 15 minutes to get accustomed to the
environment.
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5) During this time each group will prepare data entry sheets to record the results. You will be
recording the number of shrimp consumed at 1 minute intervals over a 6 minute period. Use
the table below as a guide to set up your data sheet:
Number of Brine Shrimp consumed by Mosquito Fish in Homogenous habitat
Time
(min)
0
1
2
3
4
5
6
Total
# of shrimp
consumed –
Replicate 1
0
2
3
0
0
0
0
5
# of shrimp
consumed –
Replicate 2
0
2
1
3
0
0
0
6
# of shrimp
consumed –
Replicate 3
0
0
2
3
2
0
0
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6) The class will be divided into groups so that each group monitors one of the six beakers.
7) Next you will add the brine shrimp. Cups have been provided, each containing 10 brine
shrimp in fresh water. Take one cup over to your designated beaker along with a timer
8) When you are ready, pour the contents of the cup into the beaker and immediately start
timing.
9) You must watch the beaker carefully so that you can see how many shrimp (if any) have
been consumed by the fish.
10) After each 1 minute interval, record in your data sheet how many shrimp have been eaten.
Remember, you are only recording how many shrimp have been eaten during that one
minute interval (see table above for example).
11) At the end of the 6 minute period, make sure you have all the data recorded in your table.
12) Once the experiment is complete, place the fish in the “USED” aquarium. Since our
experimental predators were not allowed to eat for 24 hours, there would be a bias in our
results if fish that had just eaten were used in another experiment.
13) Next you will need to enter your data in the tables on the board so that the entire class can
have the full data set for the 6 beakers.
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Experiment 2 – Effect of predator size on predation rates
1) You will be provided with six 1000ml beakers, each with 800ml of aerated fresh water.
2) Label three of the beakers “SMALL FISH” and the other three “LARGE FISH”
3) Next you will need to add the fish to the beakers. In each of the “SMALL FISH” beakers
you will add 1 small fish. To do this, you will use a fish net to capture a fish from the
holding tank labeled “SMALL FISH” and then GENTLY place it in the beaker. It will then
be left for 15 minutes to get accustomed to the environment.
4) In each of the “LARGE FISH” beakers you will add 1 large fish. To do this, you will use a
fish net to capture a fish from the holding tank labeled “LARGE FISH” and then GENTLY
place it in the beaker.
It will then be left for 15 minutes to get accustomed to the
environment.
5) During this time each group will prepare data entry sheets to record the results. You will be
recording the number of shrimp consumed at 1 minute intervals over a 6 minute period. Use
the table below as a guide to set up your data sheet:
Number of Brine Shrimp consumed by small Mosquito Fish
Time
(min)
0
1
2
3
4
5
6
Total
# of shrimp
consumed –
Replicate 1
0
1
1
0
0
0
0
2
# of shrimp
consumed –
Replicate 2
0
2
1
0
0
0
0
3
# of shrimp
consumed –
Replicate 3
0
0
2
1
0
0
0
3
6) The class will be divided into groups so that each group monitors one of the six beakers.
7) Next you will add the brine shrimp. Cups have been provided, each containing 10 brine
shrimp in fresh water. Take one cup over to your designated beaker along with a timer
8) When you are ready, pour the contents of the cup into the beaker and immediately start
timing.
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9) You must watch the beaker carefully so that you can see how many shrimp (if any) have
been consumed by the fish.
10) After each 1 minute interval, record in your data sheet how many shrimp have been eaten.
Remember, you are only recording how many shrimp have been eaten during that one
minute interval (see table above for example).
11) At the end of the 6 minute period, make sure you have all the data recorded in your table.
12) Once the experiment is complete, place the fish in the “USED” aquarium. Since our
experimental predators were not allowed to eat for 24 hours, there would be a bias in our
results if fish that had just eaten were used in another experiment.
13) Next you will need to enter your data in the tables on the board so that the entire class can
have the full data set for the 6 beakers.
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