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WHAT IS IT?

This model simulates the competition of three algal species (red, green, yellow) for nutrients. You can change how much the species differ in their reproductive capacity. This will decide which species ‘wins’ and gets more abundant than the others. Increasing temperature speeds up the reproduction of all algae, and, this way, accelerates the take-over of the ‘winner’.

HOW IT WORKS

Algae individuals in the model are born with a certain amount of energy. They use energy to move in the water one patch each day in a random direction. Blue patches of water represent nutrients. When an alga passes over such a patch, it takes up the nutrients and gains energy. The patch turns black, meaning there are no nutrients left, but with time nutrients regenerate.
When the energy level of an alga is over a certain amount, it reproduces. It produces a number of offsprings that can be set by sliders. The offsprings are born with identical properties (but less energy) than their parent.

HOW TO USE IT

1. Use the ‘SETUP’ button to create a certain number of individuals from each species.
2. Press the ‘GO’ button: This will start the simulation and continues running it until it is pressed again or until day 250.
3. Turn on the ‘SHOW-ENERGY?’ switch and observe the energy level of each alga.
4. Watch the ‘COUNT ALGAE’ monitor for the total number of algae and the ‘BLUE PATCHES’ for the number of patches with nutrients.
5. Look at how the number of different algal species and the amount of nutrients changes over time on the plot.

Sliders:
NUMBER_RED; NUMBER_YELLOW; NUMBER_GREEN: set the initial numbers of red, yellow and green algae respectively.

REPRODUCTION-CAPACITY_RED; REPRODUCTION-CAPACITY_RED;REPRODUCTION-CAPACITY_GREEN;REPRODUCTION-CAPACITY_YELLOW: set how many offsprings do individuals of the different species have when they reproduce.

TEMPERATURE: sets the temperature of the water. Setting it higher will make algae reproduce faster.

THINGS TO NOTICE

Look at how fast the algae consume the excess nutrients until an equilibrium sets in and the number of blue patches remains more or less constant. Setup and run the model several times and observe how many individuals you have from all three species. Is this the same in every simulation run? Why not? Turn the SHOW-ENERGY? switch on and observe how much energy the algae usually have.

THINGS TO TRY

Move the sliders to set how much offspring the algae are able to produce. How does this change the simulation outcome? Why? Set the reproduction capacities of one species higher than that of the the others, and run the model on different temperatures. Does temperature influence the outcome? Does it influence how quickly the outcome is reached?

CREDITS

This model was made by Barbara Bauer (bbauer(at)geomar.de) with NetLogo version 5.0.3. Please refer to the original when distributing or copying it.