The dead hand of Malthus...

Martin Bailey cmbb at sk.sympatico.ca
Wed Apr 24 19:56:20 EDT 2002


----- Original Message -----
From: "Kenelm Philip" <fnkwp at aurora.alaska.edu>
>
> I don't claim Malthus was wrong--he just didn't cover the whole story in
> many cases.

> 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...


Good point.

A number of years ago  I played around with the Christmas Bird Counts
results for House Sparrows (HOSP) for a number of Canadian cities. I was
wondering if HOSP numbers would be cyclical as they are with so many other
bird populations even though HOSP live in an environment which we try to
keep constant.  By the judicious  fudging of results using a variety of
univariate time series analyses I concluded that HOSP populations were
cyclical even in a steady state system - The City.

Would I repeat the study today.  No.

A new factor has entered  the equation. Merlins.  They are now found in
cities eating House Sparrows.  A more interesting study would be to see if
city based Merlin populations fluctuate.
My suspicion is that they do not.  Their excess population - 85% of
offspring don't make to the next year. Limits to growth, or something like
that.

Martin Bailey.




 
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