class=skin-invert-image|thumb|right|Plots from a standard DaisyWorld simulation.<!--A first principle of scientific charting and graphics is that you have to tell the reader, via a figure legend, what they are looking at, and not leave them to guess for themselves. This is all the more necessary for a sophisticated graphic absent a citation pointing to a corresponding, comparable published figure.--> Note, these plots are not from, nor do they correspond directly to, any data figure presented in the studies cited herein.<!--If this is incorrect, cite the study that this graphic was designed to parallel. Note, [[WP:OR is disallowed at Wikipedia.-->]]

Daisyworld is the name of a model developed by Andrew Watson and James Lovelock (published in 1983) to demonstrate how organisms could inadvertently regulate their environment. The model simulates a fictional planet (called Daisyworld) which is experiencing slow global warming due to the brightening of its star. The planet is populated by two species of daisies: black daisies and white daisies. The white daisies have a high albedo (reflectivity), and therefore have a cooling effect on the planet. The black daisies, on the other hand, have a low albedo (and thus absorb more solar radiation) and so have a warming effect on the planet. The daisies' growth rates depend on the temperature, and each daisy also affects its own microclimate in the same way as it affects the global climate. As a result, the populations of the two daisy species self-organize such that the planet remains near the optimal temperature of both daisy species (i.e. with more black daisies when the star is dimmer and more white daisies when the star is brighter). This model is called a parable because it was meant to illustrate how biotic processes could not only affect the environment (in this case the climate), but also stabilize the environment, without any planning or awareness on the part of the species involved.

Daisyworld (also sometimes referred to as "Daisy World" describe it as being formulated in response to early criticism of Lovelock's Gaia hypothesis, specifically, being a model "invented to demonstrate that planetary self-regulation can emerge automatically from physically realistic feedback between life and its environment, without any need for foresight or planning on the part of the organisms",

Given the impossibility of fully representing the "coupling" of the whole of the Earth's biota and its environment, the hypothetical model<blockquote>is an imaginary grey world orbiting, at a similar distance to the Earth, a star like our Sun that gets brighter with time. The environment... is reduced to one variable, temperature, and the biota consist of two types of life, black and white daisies, which share the same optimum temperature for growth and limits to growth. The soil of Daisyworld is sufficiently well watered and laden with nutrients for temperature alone to determine the growth rate of the daisies. The planet has a negligible atmospheric greenhouse, so its surface temperature is simply determined by... [the hypothetical star's] luminosity and its [the planet's] overall albedo <nowiki>[</nowiki>reflective power, the fraction of incident radiation reflected by the surface<nowiki>]</nowiki>, which is, in turn, influenced by the coverage of the two daisy types. W. Ford Doolittle rejected the notion of planetary regulation because it seemed to require a "secret consensus" among organisms, thus some sort of inexplicable purpose on a planetary scale. Others countered the criticism that some "secret consensus" would be required for planetary regulation, suggesting that thermoregulation of a planet beneficial to the two species arises naturally.

Later criticism of Daisyworld centers on the fact that although it is often used as an analogy for Earth, the original simulation leaves out many important details of the true Earth system. For example, the hypothetical system requires an ad-hoc death rate (γ) to sustain homeostasis, and does not take into account the difference between species-level phenomena and individual level phenomena. Detractors of the simulation believed inclusion of these details would cause the system to become unstable, making it a false analogy. These criticisms were countered by Timothy Lenton and James Lovelock in 2001, who argued that including further factors can improve climate regulation on later versions of Daisyworld.

Subsequent research

Later versions of Daisyworld, identifying the research area as "tutorial modelling of geosphere–biosphere interactions", introduced a range of grey daisies, as well as populations of grazers and predators, and found that these further increased the stability of the homeostasis.

More recently, other research, modeling real biochemical cycles of Earth, and using various types of organisms (e.g. photosynthesisers, decomposers, herbivores and primary and secondary carnivores) also argues to have produced Daisyworld-like regulation and stability, in support of ideas related to planetary biological diversity.<!--THERE IS NO MENTION OF ANYTHING REMOTELY RELATED TO DAISYWORLD, HERE: --> This enables nutrient recycling within a regulatory framework derived by natural selection amongst species, where one being's harmful waste becomes low energy food for members of another guild. For instance, research on the Redfield ratio of nitrogen to phosphorus suggests that local biotic processes might regulate global systems.

Later extension of the Daisyworld simulations which included rabbits, foxes and other species, led to the proposal that the larger the number of species, the greater thermoregulartory improvement for the entire planet, results suggesting that such a hypothetical system was robust and stable even when perturbed. Daisyworld simulations where environments were stable gradually became less diverse over time; in contrast gentle perturbations led to bursts of species richness, lending support to the idea that biodiversity is valuable.

Relevance to Earth

Because Daisyworld is so simplistic, having for example, no atmosphere, no animals, only one species of plant life, and only the most basic population growth and death models, it should not be directly compared to Earth. This was stated very clearly by the original authors. Even so, it provided a number of useful predictions of how Earth's biosphere may respond to, for example, human interference. Later adaptations of Daisyworld (discussed below), which added many layers of complexity, still showed the same basic trends of the original model.

One prediction of the simulation is that the biosphere works to regulate the climate, making it habitable over a wide range of solar luminosity. Many examples of these regulatory systems have been found on Earth.

See also

  • Gaia hypothesis
  • Gaia philosophy
  • SimEarth

Further reading

  • One review providing a 25-year retrospective of the original and subsequent related research.
  • . This work was cited as one of the two original 1983 publications by Lovelock, of the Daisyworld construct, by Wood et al. (2008), op. cit.
  • This work was cited as one of the two original 1983 publications by Lovelock, of the Daisyworld construct, by Wood et al. (2008), op. cit.
  • . This is not the first report of Daisyworld, rather, it is a followup study designed to test a specific additional question. As described carefully by Wood et al., op. cit., <small>"Watson and Lovelock [1983] reversed the sign of interaction between daisy color and planetary temperature by assuming that convection generated over the warm spots of the black daisy clumps generates white clouds above them. In this case the black daisies are still locally warmer than the white daisies, but both daisy types now cool the planet. Hence the black daisies always have a selective advantage over their white compatriots, which they drive to extinction. Yet planetary temperature is still regulated, albeit on the cold side of the optimum for growth.</small>
  • See also this author-presented web source of the full article.
  • An interview presenting the history of several topics relevant to this article, from Lovelock's perspective (with respectful reference made to W.F. Doolittle's objections).
  • A more recent, brief retrospective from Doolittle, on Gaia and related studies.

References

  • Online DaisyWorld simulator, with many options (HTML5/Javascript)
  • Java Applet for Daisyworld on a 2D space
  • Spatial Daisyworld Model Java Applet and explanation of Daisyworld with evolution
  • A Unix/X11 simulation of Daisyworld.
  • Modeling the Gaia Hypothesis: DaisyWorld A test applet of a basic Daisyworld model using a 2D cellular automata.

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  • A NetLogo version of the Daisyworld model.

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