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Daisyworld is the name of a model developed by Andrew Watson and
James Lovelock James Ephraim Lovelock (26 July 1919 – 26 July 2022) was an English independent scientist, environmentalist and futurist. He is best known for proposing the Gaia hypothesis, which postulates that the Earth functions as a self-regulating syst ...
(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 Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...
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 Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...
(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 A microclimate (or micro-climate) is a local set of atmosphere of Earth, atmospheric conditions that differ from those in the surrounding areas, often slightly but sometimes substantially. The term may refer to areas as small as a few square m ...
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"), has become a term of reference in
evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...
ary and population
ecology Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...
. It derives from research on aspects of "coupling" between an ecosphere's biota and its planetary environment, in particular via mathematical modeling and
computer simulation Computer simulation is the running of a mathematical model on a computer, the model being designed to represent the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be determin ...
, research dating to a series of 1982-1983 symposia presentations and primary research reports by James E. Lovelock and colleagues aimed to address the plausibility of the
Gaia hypothesis The Gaia hypothesis (), also known as the Gaia theory, Gaia paradigm, or the Gaia principle, proposes that living organisms interact with their Inorganic compound, inorganic surroundings on Earth to form a Synergy, synergistic and Homeostasis, s ...
. Also later referred to as a modeling of geosphere–biosphere interactions, Lovelock's 1983 reports focused on a hypothetical planet with biota (in the original work, daisies) whose growth fluctuates as the planet's exposure to its star's rays fluctuate, i.e., a pair of daisy varieties, whose differing colours drive a difference in interaction with their environment (in particular, the star). Reference to Daisyworld types of experiments have come to more broadly refer to extensions of that early work, and to further hypothetical systems involving similar and unrelated species. More specifically, given the impossibility of mathematically modeling the interactions of the full array of the biota of Earth with the full array of their environmental inputs, Lovelock introduced the idea of (and mathematical models and simulations approach to) a far simpler ecosystem—a planet at the lowest limit of its biota
orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...
ing a
star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
whose radiant energy was slowly changing—as a means to mimic a fundamental element of the interaction of all of the Earth's biota with the Sun. In the original 1983 works, Daisyworld made a wide variety of simplifying assumptions, and had white and black daisies as its only organisms, which were presented for their abilities to reflect or absorb
light Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...
, respectively. The original simulation modeled the two daisy populations—which combined to determine the planet's overall reflective power (fraction of incident radiation reflected by its surface)—and Daisyworld's surface temperature, as a function of changes in the hypothetical star's
luminosity Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...
; in doing so Lovelock demonstrated that the surface temperature of the simple Daisyworld system remained nearly constant over a broad range of solar fluctuations, a result of shifts in the populations of the two plant varieties.


Synopsis, 1983 simulation

Wood and colleagues, in a 2008 review citing the two 1983 Lovelock primary research papers on Daisyworld (still Daisy World or the same in lower case, at that point),. 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. 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
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 A greenhouse is a structure that is designed to regulate the temperature and humidity of the environment inside. There are different types of greenhouses, but they all have large areas covered with transparent materials that let sunlight pass an ...
, so its surface temperature is simply determined by... he hypothetical star's
luminosity Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...
and its he planet'soverall
albedo Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...
[reflective power, the fraction of incident radiation reflected by the surface
nowiki>]
, which is, in turn, influenced by the coverage of the two daisy types.
This hypothetical construction produces, in its mathematical modeling, a nonlinear system "with interesting self-regulating properties".


Purpose and impact

The purpose of the model is to demonstrate that feedback mechanisms can evolve from the actions or activities of self-interested organisms, rather than through classic
group selection Group selection is a proposed mechanism of evolution in which natural selection acts at the level of the group, instead of at the level of the individual or gene. Early authors such as V. C. Wynne-Edwards and Konrad Lorenz argued that the beha ...
mechanisms. 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 Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...
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 sought to demonstrate the stability of Daisyworld by making its
sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
evolve along the
main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...
, taking it from low to high
solar constant The solar constant (''GSC'') measures the amount of energy received by a given area one astronomical unit away from the Sun. More specifically, it is a flux density measuring mean solar electromagnetic radiation ( total solar irradiance) per un ...
. This perturbation of Daisyworld's receipt of
solar radiation Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible light perceptible to the human eye as well as invisible infrared (typically p ...
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 In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them und ...
world, where temperature is unregulated and rises linearly with solar output.


Criticism

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; specifically, thermoregulation was addressed. Wood and colleagues noted in 2008 that a key element in the hypothetical construct of Daisyworld was that the species of focus,
"the daisies alter the same environmental variable (temperature) in the same direction at the local level and the global level. Hence what is selected for at the individual level is directly linked to its global effects. This makes the original model a special case (and it is one that is not particularly prevalent in the real world). Evolutionary biologists often criticize the original model for this reason."
The Gaia hypothesis has otherwise 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. 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 Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...
, and found that these further increased the stability of the
homeostasis In biology, homeostasis (British English, British also homoeostasis; ) is the state of steady internal physics, physical and chemistry, chemical conditions maintained by organism, living systems. This is the condition of optimal functioning fo ...
. More recently, other research, modeling real biochemical cycles of Earth, and using various types of organisms (e.g.
photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...
ers,
decomposers Decomposers are organisms that break down dead organisms and release the nutrients from the dead matter into the environment around them. Decomposition relies on chemical processes similar to digestion in animals; in fact, many sources use the word ...
,
herbivores A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...
and primary and secondary
carnivores A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...
) also argues to have produced Daisyworld-like regulation and stability, in support of ideas related to planetary
biological diversity Biodiversity is the variability of life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and phylogenetic diversity. Diversity is not distributed evenly on Eart ...
. This enables nutrient
recycling Recycling is the process of converting waste materials into new materials and objects. This concept often includes the recovery of energy from waste materials. The recyclability of a material depends on its ability to reacquire the propert ...
within a regulatory framework derived by
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the Heredity, heritable traits characteristic of a population over generation ...
amongst
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
, 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
rabbit Rabbits are small mammals in the family Leporidae (which also includes the hares), which is in the order Lagomorpha (which also includes pikas). They are familiar throughout the world as a small herbivore, a prey animal, a domesticated ...
s, foxes and other species, led to the proposal that the larger the number of species,There are two sets of views about the role played by
biodiversity Biodiversity is the variability of life, life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and Phylogenetics, phylogenetic diversity. Diversity is not distribut ...
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 Paul Ralph Ehrlich (born May 29, 1932) is an American biologist known for his predictions and warnings about the consequences of population growth, including famine and resource depletion. Ehrlich is the Bing Professor Emeritus of Population ...
and his wife
Anne H. Ehrlich Anne Howland Ehrlich (born Anne Fitzhugh Howland; November 17, 1933) is an American scientist and author who is best known for the predictions she made as a co-author of ''The Population Bomb'' with her colleague and husband, Paul R. Ehrlich. She ...
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.
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. This finding was supported by a 1994 primary research report on
species composition Relative species abundance is a component of biodiversity and is a measure of how common or rare a species is relative to other species in a defined location or community.Hubbell, S. P. 2001. ''The unified neutral theory of biodiversity and biogeog ...
, 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". Note, the cited pages are not available via this link.


Relevance to Earth

Because Daisyworld is so simplistic, having for example, no
atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
, 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 The biosphere (), also called the ecosphere (), is the worldwide sum of all ecosystems. It can also be termed the zone of life on the Earth. The biosphere (which is technically a spherical shell) is virtually a closed system with regard to mat ...
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 Climate is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteoro ...
, 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 The Gaia hypothesis (), also known as the Gaia theory, Gaia paradigm, or the Gaia principle, proposes that living organisms interact with their Inorganic compound, inorganic surroundings on Earth to form a Synergy, synergistic and Homeostasis, s ...
* 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., "Watson and Lovelock
983 Year 983 ( CMLXXXIII) was a common year starting on Monday of the Julian calendar. Events By place Europe * Summer – Diet of Verona: Emperor Otto II (the Red) declares war against the Byzantine Empire and the Emirate of Sicily ...
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.
* See also thi
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


External links



* ttp://www.ph.ed.ac.uk/nania/daisyworld/daisyworld.html Java Applet for Daisyworld on a 2D spacebr>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.
A NetLogo version of the Daisyworld model
{{Computer modeling Climate modeling Ecological experiments Homeostasis Articles containing video clips