NH Notes: Heat Sharing Huddling Penguins – A Benefit of Selfish Behavior?

Empire penguins huddling presumably to preserve warmth.

Emperor penguins huddling presumably to preserve warmth.

In a paper entitled, “Modeling Huddling Penguins” in PLosOne (an Open Access journal) a few months ago mathematicians take on a difficult question in biology:  Do individuals organisms make decisions to share a resource for the greater good (altruism) or do they generally act only as selfish individuals.  It is very difficult to test the cause of behaviors in many animals and thus hard to determine selfish behavior from selfless behavior.    Penguins (and other animals) are observed to huddle close together in cold weather. It may seem obvious that this behavior has a positive benefit for the individuals and for the group as a whole.  But do the individuals in the group behave this way because it benefits the group or because it benefits them?  Maybe both but how can we tell?

Take the case of an individual emperor penguin in a huddling group.  How is it determined which penguin ends up at the edge of the huddle and thus bearing the brunt of the elements?  Is there a social pecking order and the ones on the outside of the huddle are the losers?  Do the ones on the outside “sacrifice” themselves for the better of the whole to no advantage of their own?  Are the ones on the outside simply the weaker penguins and are sacrificed for the good of the whole but not by their own wishes?  Or do the penguins share the responsibilities of being on the edge of the huddle?  And even if they “share” this responsibility do they share for altruistic reasons (willingly) or could they be forced to share despite their instinctual desire preserve themselves in the center?   How can these hypotheses be tested?

It has been observed for some time that penguin huddles are not static assemblages but rather the penguins are slowing and constantly moving.  That motion suggests a rotation of penguins in the huddle.  One could predict from this that penguins are rotating from the center to the outside and thus “sharing” the burden of being exposed to the elements. But the question still remains, are they rotating because they are altruistically giving each other a break against the cold and thus are sacrificing their comfortable position for the betterment of the whole group (altruistic behavior) or do they rotate for reasons less selfless?   The paper I linked to above provides mathematical modeling evidence that the penguins are in-fact acting exactly as would be predicted if they were each acting selfishly to be in the center of the group.  Penguins at the edge of a huddle are actively attempting to move away from the edge (eg. they don’t want to be cold and are trying to get away from the edge) and thus rotate to the other side of huddle where the wind is blocked.  As more penguins rotate around to the back of the huddle the ones that arrived earlier are able to push into the center of the huddle.   The penguins that started at the middle of the huddle will eventually get closer and closet to the leading edge of the moving huddle and become exposed. Thus, the models predict that over time all the penguins share time at the leading edge of the huddle and at the center of the huddle.    It is a net benefit because the long term survival of all requires that they share the stress of facing the elements otherwise the populations would be continually reduced by death or at least vastly lower reproductive success by those relegated to the edge of group.  So here we have here an interesting, and likely not at all unique, case where selfish behavior by individuals results in benefits for the entire community.

Emergent complex behavior from simple behavioral acts:

The math models of penguin motion in the face of a blizzard show us quite elegantly an example of emergent properties in living things.  Complex patterns in organisms can result from underlying simple behaviors. In this case it is predicted (and seems likely given observations of real penguin huddling behavior) that the act of penguins all shuffling to remove themselves from the harshest conditions results in the preservation of heat for the entire community which is beneficial to the survival of the whole population.   Their movement results from simple self-preservation instincts of the individual but confer greater benefits to the whole. Of course selfish is a loaded term and here I simply mean that the desire of the individual for their own comfort without consideration for the group as a whole.  This type of selfish behavior results in a net benefit to the entire group.

Below I have copied the press release associated with this article with more details about the research and its benefits.

Research Summary from Science Daily:  New Model Reveals How Huddling Penguins Share Heat Fairly 

Emperor_Huddle

Emperor penguins huddling in the bitter cold to conserve heat. What factors determine which penguins experience the most exposure? Mathematical models suggest they share the burden but not altruistically.  Copyright: the American Physiological Society

ScienceDaily (Nov. 16, 2012) — Penguins that face the bitter cold and icy winds of Antarctica often huddle together in large groups for warmth during storms. Mathematicians at the University of California, Merced created a model of penguin huddles that assumes each penguin aims solely to minimize its own heat loss. Surprisingly, the model reveals that such self-centered behavior results in an equitable sharing of heat.

The results are published in the online journal PLOS ONE and the researchers will discuss their findings at the annual meeting of the American Physical Society’s (APS) Division of Fluid Dynamics (DFD), held Nov. 18 — 20 in San Diego, Calif.

Penguins aren’t a typical study subject for Francois Blanchette, an applied mathematician at UC Merced who focuses on fluid dynamics. However, after seeing penguin huddles in the movie “The March of the Penguins” Blanchette realized that the important factors that shaped the huddle, including wind and heat flow, fell within his area of expertise.

Blanchette and his fellow researchers, Arnold Kim and Aaron Waters, modeled huddles packed so tightly that only the penguins on the outside could move. Each penguin in the huddle generated heat that the wind blew away. By considering such factors as the number of penguins in the huddle and the strength and turbulence of the wind, the model calculated which penguin on the outside of the huddle was coldest. The coldest penguin moved to the most sheltered spot available, usually relocating from a windward to a leeward position, and then the heat distribution around the huddle was recalculated. Repeated iterations showed the huddle gradually elongating and creeping downwind over time.

At first the model assumed perfectly steady wind patterns and identical penguins, but produced huddle shapes that were longer and thinner than those observed in nature. When the researchers added uncertainty, which could represent irregular wind eddies and natural differences in the size and cold tolerance of individual penguins, the modeled huddles closely matched real huddles.

The researchers were surprised the model showed the penguins shared warmth nearly equally among themselves. “Even if penguins are only selfish, only trying to find the best spot for themselves and not thinking about their community, there is still equality in the amount of time that each penguin spends exposed to the wind,” says Blanchette. Not all instances of selfish behavior result in such fair outcomes, he notes. “A penguin huddle is a self-sufficient system in which the animals rely on each other for shelter, and I think that is what makes it fair. If you have some kind of obstacle, like a wall, then I think it would stop being fair,” Blanchette says.

Currently the researchers would like feedback from biologists before they further refine the model. Gathering experimental data, however, is difficult. “Penguins huddle during blizzards, when the conditions are horrible, and if you’re going to collect data you’re also going to be in a blizzard in horrible conditions,” Blanchette points out. The mathematicians hope their work might serve as a guide for scientists in the field, helping them to know which observations to make to test the model.

Blanchette says his group may also investigate how to adapt the model to describe other biological organisms, such as certain bacteria, that move as a group in response to an outside stimulus like food or the presence of a toxin. Eventually, concepts from the model may guide the design of swarming robots that shelter each other in harsh conditions. But for now Blanchette is enjoying a more immediate side benefit of the research: “Nearly everybody seems to love penguins and not enough people love math,” he says. “If we use math to study penguins we could potentially teach more people to love math too!”

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