Daisyworld is Darwinian: Constraints on adaptation are important for planetary self-regulation

The Daisyworld model demonstrates that self-regulation of the global enviro nment can emerge from competition amongst types of life altering their loca l environment in different ways. Robertson & Robinson (1998. J. theor. Biol . 195, 129-134) presented what they describe as a "Darwinian Daisyworld" in which the ability of organisms to adapt their internal physiology in respo nse to environmental change undermines their ability to regulate their envi ronment. They assume that there are no bounds on the environmental. conditi ons that organisms can adapt to and that equal growth rates can potentially be achieved under any conditions. If adaptation could respond sufficiently rapidly to changes in the environment, this would eliminate any need for t he environment to be regulated in the first place, because all possible sta tes of the environment would be equally tolerable to life. However, the the rmodynamics, chemistry and structure of living organisms set bounds on the range of environmental conditions that can be adapted to. As these bounds a re approached, environmental conditions limit growth rate, and adaptations necessary for survival can also cost energy. Here we take account of such c onstraints and find that environmental regulation is recovered in the Daisy world model. Hence, we suggest that constraints are an important part of a self-regulating planetary system. (C) 2000 Academic Press.