One law to rule them all: Sizes within a species appear to follow a universal distribution

Mar 04, 2013
One law to rule them all: Sizes within a species appear to follow a universal distribution
© 2013 Florian Altermatt / Regula Illi - Eawag

Flocks of birds, schools of fish, and groups of any other living organisms might have a mathematical function in common. Studying aquatic microorganisms, Andrea Giometto, a researcher EPFL and Eawag, showed that for each species he studied, body sizes were distributed according to the same mathematical expression, where the only unknown is the average size of the species in an ecosystem. His article was published in in PNAS in March 2013.

Several observations suggest that the size distribution function could be universal. Giometto made his observations in the lab on 14 of aquatic , including unicellular and multicellular ones that are very distant from an evolutionary point of view. The microorganisms he studied varied by four orders of magnitude, the difference in size between a mouse and an elephant.

Furthermore, the describing the size distribution remained unchanged even when the species adapted to new environments - changes in , the presence of absence of competitors - by changing their average size.

Based on these observations, Giometto and his collaborators suggest that two separate factors work in tandem to shape the size distribution of a species. First, influence the average size of a species. Second, physiological factors, or genetics, cause the observed variability of species sizes around the average size.

From species to communities

So far the focus has been on the size distribution of individuals of a single species. But Giometto's findings become particularly interesting in light of an observation that is well known to ecologists. "If you take a cup of water from the sea and analyze all of the microorganisms it contains, you find that in an ecological community no size tends to be over or underrepresented," says Andrea Giometto. Mathematically, the sizes can be described by a power-law distribution.

Taken together, these observations of size distributions within a species and within all the species in a given ecological community have interesting implications. If in an ecosystem several species begin to converge around the same size, a balancing force will kick in to restore the power-law distribution, either by acting on the abundance or size of each species.

If, as Giometto and his co-authors speculate, their observations are valid beyond the species they studied, they may provide additional evidence for the existence of universal laws that govern natural ecosystems. These laws would regulate not only the size and abundance of organisms in an ecosystem, but also other properties, such as the number of species that co-exist.

Finding power-laws and using them to describe complex systems already has a successful track record. "In physics, the observation that systems followed power-laws was instrumental in understanding phase transitions. We believe that power-laws can be similarly helpful to gain a deeper understanding of how systems of living matter work," says Giometto, a physicist, who is seeking to apply methods from his field to understand biological ecosystems.

Explore further: The influence of the Isthmus of Panama in the evolution of freshwater shrimps in America

More information: www.pnas.org/content/early/201… /1301552110.abstract

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User comments : 4

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Lurker2358
1 / 5 (4) Mar 04, 2013
Correlation does not necessarily equal causation.

If you kill all the apex predators, I doubt an entire ecosystem would collapse, because other organisms would be made more efficient by this change. Scavengers would still be successful as well, since the apex would just be replaced by the second most successful predator, and your distribution would be slightly different.

The limit is not a law.

The limit is a solution to the sum of all laws. There's an obvious difference.
FrankHerbertWhines
1 / 5 (4) Mar 04, 2013
D U H ! !
Mandan
5 / 5 (1) Mar 04, 2013
If you kill all the apex predators, I doubt an entire ecosystem would collapse, because other organisms would be made more efficient by this change. Scavengers would still be successful as well, since the apex would just be replaced by the second most successful predator, and your distribution would be slightly different.



I don't see how your comment relates to the article.

But your comment is not true at all. You mistakenly believe that predators will suddenly shift into eating species they have never eaten before just because the species which HAS always eaten those species is no longer around to eat them.

Many predator/prey relationships are, in fact, quite specific and exclusive.

You can have all kinds of things begin to happen when a predator disappears, but the most expected one would be a sudden explosion of its prey population, which then over-consumes whatever it eats, creating multiple reverberating destructive feedback loops throughout the system.

The Teacher
1 / 5 (3) Mar 05, 2013
Accepted-JUST AS DIFFERENT SIZES OF PLANETS (including EARTH)PATHING IN DIFFERENT ROTATION IN THE UNIVERSE KEEPING US BALANCE AND FLOATING

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