DaisyWorld - A Single Daisy Ecosystem

A. Go to DaisyWorld.

B. Run the DaisyWorld model: Click on ‘Scenario' then ‘White Daisies', to run the model with only white daisies. Observe closely the two plots - the top plot shows the changes in daisy area as solar luminosity increases on DaisyWorld; the bottom plot shows the changes in temperature for both DaisyWorld and "BarrenWorld" (a barren world having no life) as solar luminosity increases.

C.  Now answer the following questions.

            1. Sketch a curve representing the growth response (rate) of the daisies to temperature. Label axes. (hint: see the Details section of the model site).

            2. What key property of the daisies results in the regulation of the planet's surface temperature?

            3. Explain the DaisyWorld feedback loop by representing:

     a) the growth response of daisies to increases in temperature at temperatures below 22.5°C; and

     b) the growth response of daisies to increases in temperature above 22.5°C. This feedback loop should include the effects on the following variables: daisy extent, planetary albedo and planet temperature.  In other words, after you figure out what happens to growth rate with increasing temperature, how does that impact daisy coverage, albedo and, ultimately, planet temperature again? You can use whatever method you would like to show the relationships between these variables under the two conditions (i.e., diagram, figure, words etc.).   

     [Hint: In one case, the temperature feedback system is positive and the effect is to keep Earth's temperature stable.  In the other case, the temperature feedback system is negative and the effect is to move Earth's temperature away from a steady state point leading to instability.  Which type of mechanism (positive or negative) is operative in a) and b) above?]

            4. As the DaisyWorld output shows, the percent area covered by daisies shows a steady increase, followed by a rapid crash. Explain this phenomenon.

            5. Based on your answers to questions 1-4, what happens to DaisyWorld temperatures when solar luminosity increases? Why is the DaisyWorld temperature response different from BarrenWorld?