DESRT WORLD

Background

Daisyworld is a model ecology with coupling between life and the environment. It shows how the adaptation of plants (daisies) can respond to and ameliorate external driving forces. The model was first proposed by Watson and Lovelock to investigate James Lovelock's Gaia hypothesis concerning feedbacks between climate and life on the Earth.

The Applet

On an imaginary planet, the sun shines (insolation) and daisies grow. The daisies may have different shade of green (albedo, from 0-1), the lighter they are, the more they reflect sunlight, cooling the planet (and vice versa). Heat diffuses across the planet via a diffusion constant (diff).

Daisies can die (fixed probability) or spread to adjacent sites: they grow best at 295.5K and the offspring colour mutates by a random amount (up to mutate).

Daisy colour gives no direct reproductive advantage, but some combinations of colours regulating the temperature better, giving a feedback which gives the whole system a growth advantage. The net effect is that the daisy colour adjusts to regulate the temperature at 295.5K. Adjust the insolation, and the mean daisy colour adjusts to compensate. If you choose a curved planet, you will find darker daisies near the pole and lighter ones at the equator.

For extreme insolations, the regulation can no longer compensate, and everything dies (yellow = bare earth). In the curved planet this can produce polar or equatorial deserts.

The feedback/diffusion process means that some parts of the planet regulate the temperature elsewhere, thus life survives longer on the curved planet, but when it breaks down the formation of a small desert (no regulation) causes positive feedback and the desert spreads to cover a whole band of the planet.

To run the applet, press the "Go!" button. While running, the "Stop" button pauses the applet, whereas the "New" button allows you to change the parameters without reseting the simulation. The "Reset" button resets the applet to new random initial conditions.

References