Darwinian Daisyworld model from and Watson & Lovelock (1983), Robertson & Robinson (1998) and Lenton & Lovelock (2001).
Units of time are 40 Myr, giving R&R's span of 10 Gyr.
This model offers many opportunities for modification. Maybe the Black and White populations can mutate into each other? The role of q as a measure of segregation of the B and W populations is interesting, and while this model uses purely stigmergic communication between species, direct interaction would also be possible.