Resource Distributions and Predator-Prey Dynamics
Day _______________________________________
Learning Objective(s):
AZ DOE---Grade 6, Strand 1, Inquiry Process
Concept 1: Observations, Questions, and Hypotheses
PO1: Differentiate among a question, hypothesis, and prediction
PO2: Formulate questions based on observations that lead to the development of a hypothesis
Concept 4: Communication
PO5: Communicate the results and conclusion of the investigation.
AZ DOE---Grade 7, Strand 4, Life Science
Concept 3: Populations of Organisms in an Ecosystem
PO2 Explain how organisms obtain and use resources to develop and thrive in:
Niches
Predator/prey relationships
PO3: Analyze the interactions of living organisms with their ecosytems
Limiting factors
Carrying capacity
AZ DOE---Grade 8, Strand 4, Life Science
Concept 4: Diversity, Adaptation, and Behaviour
PO1: Explain how an organism’s behaviour allows it to survive in an environment.
Materials:
9 Aquaria or large graduated cylinders
Sea Monkeys @ $3.00 per container
Triops @ $17.00 per kit
3 Heat Lamps and light bulbs
Thermometers
Saline Water
Syringe
Food coloring (3 colors)
9 vials per group
Pipettes
6 Flashlights
Engage
Teacher should demonstrate a thermocline and halocline in an aquarium (already set up)
to the class. The thermocline can be demonstrated using a thermometer (for a
visualization you can also place a small quantity of food coloring into the top layer and
allow the food coloring to dissipate for a few minutes but do not stir the water since
stirring will mix the layers) and the halocline can be shown by having each salinity level
5 minutes marked a unique color using food coloring.
Students should then be shown in aquarium that brine shrimp and triops have already
been established in. The teacher should then ask questions about where the animals are
located in the aquariums and what factors might be making the animals choose these
locations. Teachers can use any of the aquarium set-up designs below for their established
system, just simply add brine shrimp and triops to the set-up aquarium.
Explore
Each group of students should be given 8 vials of brine shrimp. You will want to roughly
divide the total amount of brine shrimp by the number of students in your class so that each
group will have 8 vials.
Groups of students should then cycle through the 8 stations (thermocline, halocline, light
on top of aquarium (bottom darkened), light on bottom of aquarium (top darkened), light
at top and heat lamp, light at bottom and heat lamp, light at top and halocline, and light at
20 minutes bottom and halocline) and place the contents of one vial of brine shrimp in each
aquarium. Nauplii should be slowly dripped into the aquaria by slowly pushing the
nauplii out of a pipette against the side of the aquarium.
Students should record their observations about where the brine shrimp go in each
aquarium. Students will need to pay close attention to their brine shrimp to insure that
they are following their own brine shrimp. If time permitting, you can have the students
write down their observations in a class wide table of observations on the chalk board.
You can then use this table to help further guide your questions in the section below.
Explain
The teacher should then ask the students why they think the brine shrimp are behaving
this way? What factors are influencing the brine shrimp decisions? What other factors
would also be important? Would other species of animals (i.e. predators) or more brine
shrimp affect where the current brine shrimp want to be located?
Definitions provided for food chain, community, halocline, thermocline, niche, predation
(all terms in “terms list” below).
15 minutes
Students asked to think about how these systems would be affected by a predator?
Where would the predator want to be? Why? How would the predator’s presence affect
the brine shrimp and where they want to be? Why? Note: Do not give them too much
specific guidance regarding these questions in relation to their experiment in the expand
section in order to allow the students to develop their own hypotheses. How is energy
moving through these systems?
Ask lots of questions here and really get the students involved.
Expand
Students should make a hypothesis about how one of these systems would be affected by
the introduction of a predator.
Once all of the groups have decided upon their hypothesis, the students should add triops
to their tank of interest. Note: All groups with a hypothesis regarding a specific station
must be present when the triops are added at that station.
25minutes
Students should record their observations regarding the brine shrimps location before and
after the addition of the triops as well as recording where the triops go within the
aquarium. Students should take detailed observations of how the community dynamics
and patch usages change with-in the tank.
If time permitting, students should also be given a beaker of water from a fish tank that
was inhabited by a fish to see how/if a top predator further changes the community
dynamics and patch usage.
Students should then draw conclusions based upon their observations and decide whether
their hypothesis was supported or rejected.
Evaluate
Students should fill out a worksheet identifying the different steps they used in the
scientific method to test their hypothesis (located below)
15minutes
If time permitting, students should then orally present their findings to the class
identifying how the brine shrimp assorted themselves under the different resource
structures.
Resource Distribution and Predator-Prey Dynamics:
Pre-Class Procedure:
1. Set-up each station (instructions below).
2. Divide the nauplii out between different vials so that each lab group can have 8 vials.
3. Place triops into vials so that each group can have at least one vial.
Station set-up
Station 1: Thermocline
1. Set up a heat lamp above the aquaria.
2. Allow the upper water in the aquaria to increase in temperature and establish a thermocline.
3. Test the thermocline using a thermometer. Be careful not to stir the water with the thermometer
Station 2: Halocline
1. Place a different color of food coloring in each of the different saline solutions
2. Very slowly, add each layer of water salinity to the aquarium using a pipette or syringe. Note: This will be a slow
and tedious process that should take several minutes per layer. You will want to place the densest layer of
water, the one with the highest level of salinity, on the bottom. The easiest way I have found to add the
different salinities to the aquarium is by first adding the non-saline or least saline water first. Then using a very
long syringe you can add the denser saline waters to the bottom of the aquarium by slowly dripping the saline
water out of the syringe against the bottom of the tank. You will need to make sure to not have any air bubbles
in your syringe before putting it in the tank. Optionally, you can also place a cotton ball at the bottom of the
tank and then inject your syringe into the cotton ball if you find this method to be easier.
Station 3: light on top
1. Place the aquarium in a darkened room or corner.
2. Place a flashlight (should not be one that gets hot) on the side of the upper portion of the aquarium.
3. Place a dark strip of paper below beam of light (from the flashlight) to block any light from going to the bottom
of the aquarium
Station 4: light on bottom
1. Follow same steps as Station 3 but place the flashlight on the side of the lower portion of the aquarium and the
dark strip of paper above the beam of light.
Station 5: Thermocline with light on top
1. Follow the steps under both Stations 1 (must use either an infrared or night black heat incandescent bulb)
and 3.
Station 6: Thermocline with light on bottom
1. Follow the steps under both Stations 1 (must use either an infrared or night black heat incandescent bulb)
and 4.
Station 7: Halocline with light on top
1. Follow the steps under both Stations 2 and 3.
Station 8: Halocline with light on bottom
1. Follow the steps under both Stations 2 and 4.
Terms and Definitions:
Community: A general term applied to any grouping of populations of different organisms found living
together in a particular environment
Environment: The complete range of external conditions, physical and biological, in which an organism lives.
Environment includes social, cultural, and (for humans) economic and political considerations, as well as the
more usually understood features such as soil, climate, and food supply.
Food chain: The transfer of energy from the primary producers through a series of organisms that are eaten,
assuming that each organism feeds on only one other type of organism. At each stage much energy is lost as
heat, a fact that usually limits the number of steps (trophic levels) in the chain to four or five.
Halocline: A zone in which there are rapid, vertical changes in the salinity. In low latitudes the the halocline
usually represents a decrease in salinity with increasing depth; in high latitudes it may represent the opposite.
Niche: The functional position of an organism in its environment, comprising the habitat in which in organism
lives, the periods of time during which it occurs and is active there and the resources it obtains there.
Predation: The interaction between species populations in which one organism, the predator, obtains energy
(as food) by consuming, usually killing, another, the prey.
Salinity: A measure of the total quantity of dissolved solids in water, in parts per thousand (per mille) by
weight, when all organic matter has been completely oxidized, all carbonate has been converted to oxide, and
bromide and iodide to chloride. The salinity of ocean water is in the range 33-38 parts per thousand with an
average of 35 parts per thousand.
Thermocline: Generally, a gradient of temperature change, but applied more particularly to the zone of rapid
temperature change between the warm surface waters (eplimnion) and coller deep water (hypolimnion) in a
thermally stratified lake in summer.
Trophic level: A step in the transfer of food or energy within a chain. There may be several trophic levels
within a system, for example, *producers (autotrophs), primary *consumers (herbivores, and secondary
consumers (carnivores); further carnivores may form fourth or fifth levels.
All definitions from: Allaby, Michael. Oxford: Dictionary of Ecology. Oxford University Press. Oxford, England;
1994.
Scientific Method Worksheet
1. Draw your observations regarding where the nauplii congregated at each station.
2. Why are the nauplii behaving in this manner?
3. As a result of your observations today, what are some examples of questions you had regarding how
predators might influence the congregation of nauplii around the different resources (light,
temperature, salinity)?
4. What was your hypothesis?
5. What was the prediction that you made for what would happen in your experiment?
a. Was your prediction correct?
b. Does this mean that your hypothesis was supported or rejected?
c. Why?
6. What conclusions can you draw from this experiment?
7. How is the nauplii’s behaviour beneficial to their survival?
8. Now imagine another predator has been added to this system. How would this further change the
community assembly within your system?