Daisyworld is a simple model designed to show the long-term effects of coupling between life the abiotic environment at a planetary scale. The model was originally described by James Lovelock and Watson in defense of Lovelock’s Gaia theory which suggests that Earth is a self-regulating homeostatic system whose activity maintains the conditions necessary for biological life. The model has transcended the original theory and become widespread across the scientific community as a paradigm for considering the role of biota in the Earth system and a teaching tool for new researchers due to the model’s simplicity.
Model Description
Daisyworld consists of two classes of daisy, one black and one white, that share space on a planet who’s temperature is driven by the luminosity of the sun. The two classes can be considered as distinct species or as distinct phenotypes within the same species. The albedo of each daisy results in either greater light absorption (black daisies) or greater light reflectance (white daisies). The population growth equations that determine the change in area coverage of each species is as follows:
\frac{dW}{dt} = W[e{\beta}(T_W)-\gamma]\frac{dB}{dt} = B[e{\beta}(T_B)-\gamma]Each population change equation follows the traditional form of births (eβ(T)) minus losses (γ). Births are scaled initially by the amount of uninhabited surface area on the planet:
e = area_{planet} - area_W-area_BThen they are scaled by a single-peaked functional form that determines fitness:
{\beta}(T) = 1-k(T-T_{optimal})Here, k is a scalar that determines the difference between the current temperature (T) and the ideal temperature for daisy growth (T optimal) under which growth is still possible. The lower that difference, the higher the birth rate of the daisies. Each daisy type maintains a local temperature (T_W and T_B) that is determined as follows:
T_g^4 = q(A-a_g) + T^4
Model Results
