The dead hand of Malthus...

Kenelm Philip fnkwp at
Wed Apr 24 14:28:10 EDT 2002

> If you can take habitat size as a constant - and not as a shrinking
> factor - natural systems do work as Mathus postulated.

I don't claim Malthus was wrong--he just didn't cover the whole story in
many cases. Let's consider two species of leps:

1) _Phyllocnistis populiella_ (aspen serpentine leaf miner). A few years
ago, nearly every aspen in the Fairbanks area had two mines (one on the
top surface, one on the bottom) on almost every leaf. Clearly, the pop-
ulation was being limited by the amount of food--that year. In other years,
the numbers have been much smaller--showing that one or more other factors
were at work. The number of aspen leaves stays roughly constant from
year to year...

2) Nymphalis antiopa_ (mourning cloak). The foodplant is willow, and there
is _lots_ of willow here. If the population were limited by food, we would
see the sky darkened by mourning cloaks (which would be an interesting
sight). Instead this species' numbers fluctuate about some much lower
level such that you don't normally see totally defoliated willows (the
usual result of their colonial feeding behavior) in the wild. In this
case I don't think Malthusian considerations apply to the _antiopa_ it-
self. They may apply to its parasites, however.  :-)

							Ken Philip


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