Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Rock-Paper-Scissors Tournaments Explain Ecological Diversity

16.03.2011
The mystery of biodiversity – how thousands of similar species can co-exist in a single ecosystem – might best be understood as the result of a massive rock-paper-scissors tournament, a new study has revealed.

According to classical ecology, when two species compete for the same resource, eventually the more successful species will win out while the other will go extinct. But that rule cannot explain systems such as the Amazon, where thousands of tree species occupy similar ecological niches.

The childhood game of rock-paper-scissors provides one solution to this puzzle, report researchers at the University of Chicago and the University of California, Santa Barbara in Proceedings of the National Academy of Sciences. A mathematical model designed around the game's dynamics produced the potential for limitless biodiversity, and suggested some surprising new ecological rules.

"If you have two competitors and one is better, eventually one of the two will be driven extinct," said co-author Stefano Allesina, PhD, assistant professor of ecology and evolution at the University of Chicago. "But if you have three or more competitors and you use this rock-paper-scissor model, you can prove that many of these species can co-exist forever."

The rock-paper-scissors rules are an example of an "intransitive" competition, where the participants cannot be simply ordered from best to worst. When placed in pairs, winners and losers emerge: rock beats scissors, paper beats rock, and scissors beat paper. But when all three strategies compete, an impasse is reached where no one element is the undisputed winner.

In nature, this kind of rock-paper-scissors relationship has been observed for three-species groups of bacteria and lizards. But scientists had not yet studied how more complex intransitive relationships with more than three players – think rock-paper-scissors-dynamite, and beyond – could model the more complex ecosystems.

"No one had pushed it to the limit and said, instead of three species, what happens if you have 4,000? Nobody knew how," Allesina said. "What we were able to do is build the mathematical framework in which you can find out what will happen with any number of species."

Allesina and co-author Jonathan Levine, PhD, professor of ecology, evolution & marine biology at UCSB, combined the advanced mathematics of game theory, graph theory, and dynamical systems to simulate the outcome when different numbers of species compete for various amounts of "limiting factors" with variable success. An example, Allesina said, is a group of tree species competing for multiple resources such as nitrogen, phosphorus, light, and water.

When more limiting factors are added to the model, the amount of biodiversity quickly increases as a "tournament" of rock-paper-scissors matches develops between species, eliminating some weak players but maintaining a stable balance between multiple survivors.

"What we put together shows that when you allow species to compete for multiple resources, and allow different resources to determine which species win, you end up with a complex tournament that allows numerous species to coexist because of the multiple rock-paper-scissors games embedded within," Levine said.

In some models, where each species' advantage in one limiting factor is coupled to a disadvantage on another, a mere two limiting factors is capable of producing maximal biodiversity – which stabilizes at half the number of species originally put into the model, no matter how large.

"It basically says there's no saturation," Allesina said. "If you have this tradeoff and have two factors, you can have infinite species. With simple rules, you can create remarkable diversity."

The model also produced a strange result: when the limiting factors are uniformly distributed, the total number of species that survive is always an odd number. Adjusting the model's parameters to more closely model the uneven distribution of resources in nature removed this intriguing quirk.

Allesina and Levine tested the realism of their model by successfully reverse-engineering a network of species relationships from field data on populations of tropical forest trees and marine invertebrates. Next, they will test whether the model can successfully predict the population dynamics of an ecosystem. Recently, Allesina was awarded a $450,000 grant by the James S. McDonnell Foundation to conduct experiments on bacterial populations that test the rock-paper-scissors dynamics in real time.

In the meantime, the rock-paper-scissors model proposes new ideas about the stability of ecosystems – or the dramatic consequences when only one species in the system is removed.

"The fact that many species co-exist could depend on the rare species, which are more likely to go extinct by themselves. If they are closing the loop, then they really have a key role, because they are the only ones keeping the system from collapsing," Allesina said.

"If you're playing rock-paper-scissors and you lose rock, you're going to end up with only scissors in the system," Levine said. "In a more complex system, there's an immediate cascade that extends to a very large number of species."

The paper, "Competitive network theory of species diversity," was published online by the Proceedings of the National Academy of Sciences on March 14, 2011. The research was supported by the James S. McDonnell Foundation and the National Science Foundation.

Robert Mitchum | Newswise Science News
Further information:
http://www.uchospitals.edu

More articles from Ecology, The Environment and Conservation:

nachricht Upcycling 'fast fashion' to reduce waste and pollution
03.04.2017 | American Chemical Society

nachricht Litter is present throughout the world’s oceans: 1,220 species affected
27.03.2017 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

Im Focus: Quantum-physical Model System

Computer-assisted methods aid Heidelberg physicists in reproducing experiment with ultracold atoms

Two researchers at Heidelberg University have developed a model system that enables a better understanding of the processes in a quantum-physical experiment...

Im Focus: Glacier bacteria’s contribution to carbon cycling

Glaciers might seem rather inhospitable environments. However, they are home to a diverse and vibrant microbial community. It’s becoming increasingly clear that they play a bigger role in the carbon cycle than previously thought.

A new study, now published in the journal Nature Geoscience, shows how microbial communities in melting glaciers contribute to the Earth’s carbon cycle, a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

New quantum liquid crystals may play role in future of computers

21.04.2017 | Physics and Astronomy

A promising target for kidney fibrosis

21.04.2017 | Health and Medicine

Light rays from a supernova bent by the curvature of space-time around a galaxy

21.04.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>