The dead hand of Malthus...

[Kenelm Philip]

	Martin Bailey mentioned the lynx/hare cycle as an example of an
organism controlled by its food supply. It is worth noting the following:
The often-quoted data on hares and lynxes from the Hudson's Bay Company
records show an approx. 10-year cycle for lynxes and an approx. 4-year
cycle for hares, over a 220-year period. These data do not support a
Lotka-Volterra prey-predator interaction. However, the real problem is
that the hare data and the lynx data were taken from different parts of
Canada--so we are talking about the prey the lynx _would_ have fed upon
had they been there! As someone said a long time ago: "It's not what you
don't know that's the problem--it's what you _do_ know that's wrong."

	Another famous case of prey-predator interaction is the mule deer
on the Kaibab Plateau, which were supposed to have had a population
explosion after the removal of mountain lions, and then a crash due to
having consumed all the food available. A 1970 paper by Graeme Caughley
concluded that the 'irruption' may or may not have occuured at all, and
if it did may have been caused by other factors unrelated to predators.

	It is a human tendency to see order where none exists. This tend-
ency leads people to accept even over-simplified theories, because they
impose that so-much-desired order upon the natural world.

							Ken Philip




 
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