Lemming Population Flux Solved: Mass Suicide Not to Blame 181
quogmire writes "Australia's ABC reports that biologists from the Universities of Finland and Freiburg (Germany) have finally solved the question of lemming population fluctuations once thought to be caused by lemmings mass-suiciding by plunging off cliffs. 'Lemming populations, they say, surge spectacularly and fall just as quickly, thanks to the combined feasting of four predators: the stoat, arctic fox, snowy owl and a seabird called the long-tailed skua.' The original article (Login required) is published in Science."
Suicide theory is a fraud! (Score:5, Informative)
It's well known, by me at least, that the whole 'lemming suicide' thing was something that Disney cooked up during their 'bad documentary' era. In this case the lemmings were hearded off a cliff by the documentary crew, and was filmed as a 'mass suicide'.
I've seen some pretty amusing/sad documentaries that came out of Disney, including one that had the antics of a Jaguar eating various creatrues. It was OBVIOUS that it was a jaguar in a rather well done habitat where they threw in various animals, mostly eels, for the jaguar to attack. It was exceptionally amusing, but sad, too, that they thought to do something like this and pass it off as truth.
Re:Suicide theory is a fraud! (Score:3, Informative)
http://www.snopes.com/disney/films/lemmings.htm
Re:Suicide theory is a fraud! (Score:5, Informative)
RTFA? (Score:4, Informative)
But I just wanted to point out that the ABC article is somewhat misleading. The original research article at no point addresses or attempts to refute the mass-suicide myth. Because, honestly, no scientist believed that was possible. The question they considered was much more reasonable: do the large deviations come from predators eating lemmings, or from a lack of vegatation for the lemmings to eat? It seems as though they have resolved that the crashes in population come from predator over-population, not from food scarcity.
This article will probably not shake the foundations of population dynamics. As some other posters have pointed out, it is not so surprising that one sees immense highs and massive crashes in a predator-prey system, because these phenomena exist even in simple mathematical models of pred-prey systems. So for a mathematician this should fly right under the radar.
On the other hand, to a population dynamics guy, this is somewhat interesting, as in that field it is typically considered hard to model these dynamics accurately. It seems as though these guys have determined some parameters in the population dynamics model experimentally, and this is what it is interesting.
Re:University of Finland? (Score:3, Informative)
I'm afraid you're mistaken (Score:3, Informative)
I'm afraid you misread that. The post says "Universities of Finland and Freiburg (Germany)", while the ABC article says "University of Finland, and Benoit Sittler of the University of Freiburg in Germany."
The university in question is the University of Helsinki, Finland. (I have university access to the Science articles.)
Re:Carrying capacity (Score:3, Informative)
Re:Carrying capacity (Score:2, Informative)
This is very true. But it is true in the one-dimensional case, which I claim is the case for the dynamics of the population of humans.
All that being said, why does the model for the population have to be one-dimensional? This is a reasonable objection. An answer to that is, no matter how many dimensions the system has, there should be a way to coarse-grain it and get an essentially 1-D system.
For example, let the population of humans be P(t). If we make the assumption that the growth rate of humanity depends only upon the number of people alive, then it can be written
dP/dt = f(P) P,
where f(P) is some unknown function which absorbs all of the possible variables. For example, we could say that there are thousands of factors which impinge on the growth rate of people, like availability of food, prevalence of pollution, etc. Now, our only assumption is that all of these factors depend on the size of the population. Then we can say that the growth rate is really a function only of P.
Now, to be fair, it is possible that there are factors which don't depend on the size of the population. But I think it is reasonable, in that all of the standard constraints to growth, like prevalence of pollution, limits of food, etc., can depend only on population.
Now, if this model is correct, then it is true that this system is not chaotic at all, but that there is complete regularity. For example, as long as it is true that for sufficiently large P, this function f(P) is negative, then there is a number, called the carrying capacity for the system, and any initial population will tend towards it.
I do agree that it is possible that this function f can depend on some other things, for example imagine that for some strange reason, tomorrow the availability of the food supply takes a big hit, and that f becomes much smaller without P changing. Then we could have a crash of some sort, but my feeling is that although this is possible, it's not reasonable. I think that on the other hand it is reasonable to expect that this function f will depend only on P.