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Daisyworld

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Plots from a standard black & white DaisyWorld simulation.[citation needed]

Daisyworld, a term of reference in evolutionary ecology, refers to research work on geosphere–biosphere interactions, in particular modeling by computer simulation to address plausibility of the Gaia hypothesis, focusing on a hypothetical planet with biological populations that fluctuate as the planet's exposure to its sun's rays fluctuate.[1][non-primary source needed][2][verification needed] In the original 1983 work, by Andrew Watson and James Lovelock, the ecosystem was composed of two varieties of daisy (genus Asteraceae).[3] The term more broadly refers to subsequent extensions of that work to further hypothetical systems of these and further species.[2][verification needed]

Lovelock and Watson introduced the notion of a simple ecosystem on a planet orbiting a star whose radiant energy is slowly changing to mimic elements of the Earth-Sun system and the Earth's ecosystem.[citation needed] In the original 1983 work, Daisyworld had white and black daisies as its only life forms, which were presented for their abilities to reflect or absorb light, respectively.[citation needed] The original simulation tracks the two daisy populations and Daisyworld's surface temperature as a function of fluctuations in the sun's rays, and demonstrated that the surface temperature of that simple, hypothetical Daisyworld remained nearly constant over a broad range of solar fluctuations.[citation needed]

Synopsis, 1983 simulation

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Wood and colleagues, in a 2008 review citing the two 1983 Lovelock primary research papers on Daisyworld, 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",[2]

Given the impossibility of fully representing the "coupling" of the whole of the Earth's biota and its environment, the hypothetical model

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 [reflective power, the fraction of incident radiation reflected by the surface], which is, in turn, influenced by the coverage of the two daisy types.[2]

This hypothetical construction produces, in its mathematical modeling, a nonlinear system "with interesting self-regulating properties".[2]

Purpose and impact

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A short video about the DaisyWorld model and its implications for real world earth science.[citation needed]

The purpose of the model is to demonstrate that feedback mechanisms can evolve from the actions or activities of self-interested[clarification needed] organisms, rather than through classic group selection mechanisms.[3][non-primary source needed][verification needed] Daisyworld examines the energy budget of a planet populated by two different types of plants, black daisies and white daisies. The colour of the daisies influences the albedo of the planet such that black daisies absorb light and warm the planet, while white daisies reflect light and cool the planet. Competition between the daisies (based on temperature-effects on growth rates) leads to a balance of populations that tends to favour a planetary temperature close to the optimum for daisy growth.

Lovelock and Watson sought to demonstrate the stability of Daisyworld by making its sun evolve along the main sequence, taking it from low to high solar constant. This perturbation of Daisyworld's receipt of solar radiation caused the balance of daisies to gradually shift from black to white but the planetary temperature was always regulated back to this optimum (except at the extreme ends of solar evolution). This situation is very different from the corresponding abiotic world, where temperature is unregulated and rises linearly with solar output.

Criticism

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Daisyworld was designed to refute the idea that there was something inherently mystical about the Gaia hypothesis that Earth's surface displays homeostatic and homeorhetic properties similar to those of a living organism;[citation needed] specifically, thermoregulation was addressed.

The Gaia hypothesis had attracted a substantial amount of criticism from scientists, e.g., Richard Dawkins, who argued that planet-level thermoregulation was impossible without planetary natural selection, which might involve evidence of dead planets that did not thermoregulate.[4][page needed] 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.[5][6] 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.[7][non-primary source needed][verification needed]

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.[citation needed] 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.[citation needed] Detractors of the simulation believed inclusion of these details would cause the system to become unstable, making it a false analogy.[citation needed] These criticisms were countered by Timothy Lenton and James Lovelock in 2001, who argued that including further factors can improve climate regulation on later versons of Daisyworld.[8][non-primary source needed]

Subsequent research

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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.[8][1][non-primary source needed]

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.[citation needed] 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.[citation needed] For instance, research on the Redfield ratio of nitrogen to phosphorus suggests that local biotic processes might regulate global systems.[9][non-primary source needed]

Later extension of the Daisyworld simulations which included rabbits, foxes and other species, led to the proposal that the larger the number of species,[10] the greater thermoregulartory improvement for the entire planet, results suggesting that such a hypothetical system was robust and stable even when perturbed.[11][page needed] 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.[11][page needed]

This finding was supported by a 1994 primary research report on species composition, dynamics, and diversity in successional and native grasslands in Minnesota by David Tilman and John A. Downing, which concluded that "primary productivity in more diverse plant communities is more resistant to, and recovers more fully from, a major drought". They go on to add that their "results support the diversity stability hypothesis but not the alternative hypothesis that most species are functionally redundant".[12][non-primary source needed][13][verification needed]

Relevance to Earth

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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.[citation needed]

See also

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Further reading

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  • Andrew J. Wood; G. J. Ackland; J. G. Dyke; H. T. P. Williams; T. M. Lenton (January 5, 2008). "Daisyworld: A review". Reviews of Geophysics. 48 (RG1001): RG1001. Bibcode:2008RvGeo..46.1001W. doi:10.1029/2006RG000217. One review providing a 25-year retrospective of the original and subsequent related research.
  • Mossman, Kate & Lovelock, James (July 31, 2019). "James Lovelock at 100: "My Life Has Been One Mass of Visions"" (interview). NewStatesman.com. London, England: New Statesman Limited. Retrieved July 24, 2024.{{cite journal}}: CS1 maint: multiple names: authors list (link) 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).

References

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  1. ^ a b von Bloh, W.; Block, A.; Parade, M.; Schellnhuber, H. J. (April 15, 1999). "Tutorial Modelling of Geosphere–Biosphere Interactions: The Effect of Percolation-Type Habitat Fragmentation" (PDF). Physica A: Statistical Mechanics and Its Applications. 266 (1): 186–196. Bibcode:1999PhyA..266..186V. doi:10.1016/S0378-4371(98)00590-1. ISSN 0378-4371.[non-primary source needed]
  2. ^ a b c d e Andrew J. Wood; G. J. Ackland; J. G. Dyke; H. T. P. Williams; T. M. Lenton (January 5, 2008). "Daisyworld: A Review". Reviews of Geophysics. 48 (RG1001): RG1001. Bibcode:2008RvGeo..46.1001W. doi:10.1029/2006RG000217.
  3. ^ a b Watson, A.J.; J.E. Lovelock (1983). "Biological Homeostasis of the Global Environment: The Parable of Daisyworld". Tellus B. 35 (4): 286–9. Bibcode:1983TellB..35..284W. Retrieved July 24, 2024.
  4. ^ Dawkins, R (1982). The Extended Phenotype: The Long Reach of the Gene. Oxford University Press. ISBN 0-19-286088-7.[full citation needed]
  5. ^ Doolittle, W.F. (Spring 1981). "Is Nature Really Motherly?". The Coevolution Quarterly: 58–63.
  6. ^ Incidentally, neither of these Neo-Darwinians made a close examination of the wide-ranging evidence presented in Lovelock's books that was suggestive of planetary regulation, dismissing the theory based on what they saw as its incompatibility with the latest views on the processes by which evolution works.[according to whom?][citation needed]
  7. ^ Sagan, D. & Whiteside, J.H. (2004). "Gradient-Reduction Theory: Thermodynamics and the Purpose of Life". In Stephen H. Schneider; James R. Miller; Eileen Crist; Penelope J. Boston (eds.). Scientists Debate Gaia: The Next Century. MIT Press. pp. 173–186. doi:10.7551/mitpress/9780262194983.003.0017.{{cite book}}: CS1 maint: multiple names: authors list (link)[non-primary source needed]
  8. ^ a b Lenton, T. M.& Lovelock, J.E. (2001). "Daisyworld Revisited: Quantifying Biological Effects on Planetary Self-Regulation". Tellus Series B. 53 (3): 288–305. Bibcode:2001TellB..53..288L. doi:10.1034/j.1600-0889.2001.01191.x.{{cite journal}}: CS1 maint: multiple names: authors list (link)[non-primary source needed]
  9. ^ Downing, Keith & Zvirinsky, Peter (October 1, 1999). "The Simulated Evolution of Biochemical Guilds: Reconciling Gaia Theory and Natural Selection". Artificial Life. 5 (4): 291–318. Retrieved July 24, 2024.{{cite journal}}: CS1 maint: multiple names: authors list (link)[non-primary source needed]
  10. ^ There are two sets of views about the role played by biodiversity in the stability of ecosystems in Gaia theory. In one school of thought labelled the "species redundancy" hypothesis, proposed by Australian ecologist Brian Walker, most species are seen as having little contribution overall in the stability, comparable to the passengers in an aeroplane who play little role in its successful flight. The hypothesis suggests that only a few key species are necessary for a healthy ecosystem. The "rivet-popper" hypothesis put forth by Paul R. Ehrlich and his wife Anne H. Ehrlich compares each species forming part of an ecosystem with a rivet on the aeroplane (represented by the ecosystem). The progressive loss of species mirrors the progressive loss of rivets from the plane, weakening it till it is no longer sustainable and crashes. See Leakey & Lewin (1996), op. cit.
  11. ^ a b James Lovelock (2000) [1988]. The Ages of Gaia: A Biography of Our Living Earth (2nd, rev. ed.). Oxford University Press. pp. 213–216. ISBN 978-0-19-286217-4.
  12. ^ Tilman, David & Downing, John A. (1994). "Biodiversity and Stability in grasslands" (PDF). Nature. 367 (6461): 363–365. Bibcode:1994Natur.367..363T. doi:10.1038/367363a0. S2CID 4324145. Archived from the original (PDF) on September 27, 2011.{{cite journal}}: CS1 maint: multiple names: authors list (link)[non-primary source needed]
  13. ^ Leakey, Richard E. & Lewin, Roger (1996). The Sixth Extinction: Patterns of Life and the Future of Humankind. New York, NT: Penguin Random House-Knopf Doubleday. pp. 137–142. ISBN 9780385468091. Retrieved July 24, 2024.{{cite book}}: CS1 maint: multiple names: authors list (link) Note, the cited pages are not available via this link.
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