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(29 pts)
BE SURE TO PAUSE THE VIDEO AS YOU ANSWER EACH QUESTION, ESPECIALLY WHEN ASKED TO MAKE PREDICTIONS.
This exercise is based on a series of famous experiments conducted in the 1960’s along the rocky shore of Washington state, in the northwestern United States (Paine, 1966: Am. Nat. 100: 65-75; Paine, 1969: Ecology 50: 950-961). The intertidal community is comprised of organisms living in the area covered by water at high tide and exposed to the air at low tide. The nine species in this laboratory’s simulated rocky intertidal area include three different algae; three stationary (or “sessile”) filter-feeders; and three mobile consumers.
The following table provides information on the species that you will encounter in this simulation
COMMON NAME OF ORGANISM (GENUS) TYPE OF ORGANISM PRODUCER
OR CONSUMER? FILTER FEEDER?
(YES / NO) STATIONARY OR MOBILE?
Nori Seaweed (Porphyra) Algae Producer NO Stationary
Black Pine (Neorhodomela) Algae Producer NO Stationary
Coral Weed (Corallina) Algae Producer NO Stationary
Mussel (Mytilus) Mollusk Consumer YES Stationary
Acorn Barnacle (Balanus) Crustacean Consumer YES Stationary
Goose Neck Barnacle (Mitella) Crustacean Consumer YES Stationary
Whelk (Nucella) Mollusk Consumer NO Mobile
Chiton (Katharina) Mollusk Consumer NO Mobile
Starfish (Pisaster) Echinoderm Consumer NO Mobile
In this laboratory, you’ll use simulated experiments to elucidate how interactions between species can play a major role in determining community structure. You will apply techniques similar to those used in the original studies.
In the competitive dominance hierarchy diagram below, the arrows point from weaker to stronger competitors. For example, the arrow pointing from Nori Seaweed to Black Pine indicates that Black Pine is dominant over (i.e., can displace) Nori Seaweed. Next to each species name, indicate how many arrows point to that species. The highest number indicates the most highly ranked and aggressive, or “best”, competitor. Which species is the dominant competitor? (2 pts)
You will now examine the predator-prey interactions that occur in the rocky intertidal zone.
This table provides information on the prey each of the predators consumes.
STARFISH WHELK CHITON
Prey Species: Mussel Gooseneck Barnacle Black Pine
Percentage of Diet: 60% 50% 40%
Prey Species: Gooseneck Barnacle Acorn Barnacle Nori Seaweed
Percentage of Diet: 40% 50% 30%
Prey Species: Coral Weed
Percentage of Diet: 30%
Use this data on feeding relationships to construct a food web diagram for the organisms that live in the simulated intertidal zone. Link the species names below with arrows that point from prey to consumer. (3 pts)
Based on your studies so far, you know important details about the competitive and feeding relationships among the species in your simulated intertidal community, and these relationships, when integrated, define the role played by each. One way to more fully elucidate the importance of a species to its community structure is to remove it from the environment and observe what happens. In this exercise, you will experimentally determine how removing each of the highest trophic level species (the mobile consumers) affects the rocky intertidal community structure.
Before you start your experiments, you will first make some predictions. Refer back to your data to inform your answers. [NOTE: only one species will be removed in each experiment.]
[ 1.1 ] In the spaces provided below, predict which other species in the community will be impacted the most by each removal and explain your reasoning. (6 pts)
Predicted impact of removing Whelk and explanation:
Predicted impact of removing Chiton and explanation:
Predicted impact of removing Starfish and explanation:
[ 1.2 ] One removal experiment will have a more dramatic impact than the other two. Write down which one you predict this will be, and why: (2 pts)
[ 2 ] Select “Who Rules the Rock?” from the Select an Exercise menu.
[ 3 ] Your first step is to record population sizes BEFORE REMOVALS. To make sure the simulation is initialized correctly, click the RESET button. A data table is provided on the next page for recording your results.
HELFUL HINT: if you click on the colored bars in the Population Size graph, the numbers (population sizes) that the bars represent will pop up!
[ 3.1 ] In the table on the next page, record the population size of each species at ‘Time Elapsed = 0 Weeks’ in the BEFORE REMOVALS column.
[ 4 ] After recording data BEFORE REMOVALS, you are ready to remove mobile consumers. Find the REMOVE WHELK button (which is round and depicts a Whelk with a slash through it) in the TOOLS PANEL. When you click this button, all Whelk will vanish from the Intertidal Zone.
[ 5 ] For each removal experiment, you will run the simulation for 200 weeks (in model time, not real time!). To do this, first make sure that the Time Elapsed = 0 weeks (RESET if not), and then click the STEP 200 button in the CONTROL PANEL..
[ 6 ] Confirm that the simulation stopped at (or near) 200 weeks. If so, click the bars in the Population Size graph and record the abundance of each species.
[ 6.1 ] In the data table, record the population size of each species in the AFTER WHELK REMOVAL column. (1 pt)
[ 7 ] RESET the simulation and confirm that Time Elapsed = 0 weeks. Then click the REMOVE CHITON button to remove all Chiton from the Intertidal Zone.
[ 8 ] Click the STEP 200 button to run the simulation for 200 weeks.
[ 8.1 ] When Time Elapsed = 200 weeks, record the population size of each species in the AFTER CHITON REMOVAL column. (1 pt)
[ 9 ] Finally, RESET the simulation and use the REMOVE STARFISH tool and the STEP 200 button to repeat the experiment for Starfish.
[ 9.1 ] In the data table, record the population size of each species in the AFTER STARFISH REMOVAL column. (1 pt)
Abundance Data for Removal Experiments
SPECIES BEFORE
REMOVALS AFTER WHELK REMOVAL AFTER CHITON REMOVAL AFTER STARFISH REMOVAL
Nori
Black Pine
Coral Weed
Mussel
Acorn Barnacle
Goose Neck Barnacle
Whelk 0
Chiton 0
Starfish 0
[ 10 ] When your data table is complete, answer the following questions. Try to be as quantitative as possible with your answers, indicating by approximately how much each species increased or decreased in size (e.g., “The Starfish population more than doubled”; “The population of Coral Weed decreased to about half its original size.”).
[ 10.1 ] What were the most dramatic changes to the community after Whelk were removed? (2 pts)
[ 10.2 ] What were the most dramatic changes to the community after Chiton were removed? (2 pts)
[ 10.3 ] What were the most dramatic changes to the community after Starfish were removed? (2 pts)
[ 10.4 ] Which removal had the greatest impact upon the rest of the community? (2 pts)
[ 10.5 ] Referring back to your competitive dominance hierarchy and food web diagrams, try to explain what happened in the removal experiment that had the greatest impact on community structure. Why was the effect so pronounced? In other words, why was that species a keystone predator? (5 pts)