Bill/Forum,
May I/we have the Weigert reference/link, please?
Does anyone (Weigert?) have any idea WHY performance goes down as complexity
goes up? Is it because we humans have trouble with more that a small handful of
variables or is it the nature of the program? Is it because the phenomena we're
trying to observe are bigger than we in space and time, not to mention degree
or quality ("he said fuzzily")?
Why is it that some of us now and then come to a point where it seems clear,
when we have dropped our objective guards and spears, and we fall down some
rabbit or worm hole into some place other than our conscious minds and find, to
our surprise, that, as Edna St. Vincent Millay once put it, "I found that I had
translated the line."*
Speaking of predator-prey population dynamics, has anybody ever figured out
"mouse plagues?"
On "avoiding parameters," to put it poetically (Robert Frost, The Mending
Wall): "Before I built a wall I'd ask to know ~ What I was walling in or
walling out." I presume you did. But does everybody?
With respect to your other email, several years ago I suggested fuzzy logic to
a sizeable (regional) group of ecologists . . . The atmosphere was, shall we
say, odd. I got one linear question about how one could do real science that
way. All else was silence.
WT
*For those interested in the context: "My attention was caught by a line in
quite another poem; and a few minutes later, with something of the terror which
a person must feel who realizes that he has undoubtedly been bitten by a
mosquito and that he is in a notoriously malarial climate, I found that I had
translated the line! I was breathing hard. . .I had entirely forgotten what I
was looking up. . .Fatally in my mind was the sickening conviction that I was
in for it, that I had caught the fever, and that neither quinine nor wise
counsel could save me." --Edna St. Vincent Millay on translating Les Fleurs du
Mal [Her introduction to the translation, "Flowers of Evil." (From
http://geocities.com/bostonpoet2000/articles/trans.html )]
----- Original Message -----
From: "William Silvert" <[email protected]>
To: <[email protected]>
Sent: Friday, January 23, 2009 3:07 AM
Subject: Re: [ECOLOG-L] Subject: Ecology Certainty Uncertainty
Illusion/Delusion, was Re: Ecological Modelling
> Highly detailed models seldom work well. In a classic paper by Weigert he
> showed that the best models have an intermediate level of complexity beyond
> which performance gets worse. The interactions between closely related
> species are so difficult to quantify that some degree of aggregation is
> essential.
>
> Galtman didn't specify what the purpose of the model was and what he
> expected it to do, but for a long time people have modelled predator-prey
> systems successfully. We did this by avoiding the use of parameters that we
> couldn't measure. Sure the models don't answer every question, but so long
> as they answer the questions we posed that was enough.
>
> That doesn't mean that every question can be answered by modelling. Many
> years ago we had a joint workshop with the fishing industry and they wanted
> us to predict biomasses of cod and haddock. I pointed out that we had
> already developed a model that predicted the total landings of cod+haddock,
> but the two stocks varied unpredictably with inverse correlation so that we
> could not break the total down into the two components. They were
> dissatisfied with that, but that was the best we could do.
>
> Bill Silvert
>
>
> ----- Original Message -----
> From: "joseph gathman" <[email protected]>
> To: <[email protected]>
> Sent: Thursday, January 22, 2009 9:12 PM
> Subject: [ECOLOG-L] Subject: Ecology Certainty Uncertainty
> Illusion/Delusion, was Re: Ecological Modelling
>
>
>>> That means, I suspect, that ecology is, in the view of literal believers,
>>> > "doomed" to be "applied."
>>
>> I don't know about that, but I DO think that what may well be doomed is
>> our ability to accurately model complex systems. In my own limited
>> attempt at modelling, I tried to model a simple predator-prey system, but
>> it quickly led me into a rat's nest of uncertainties. It would have taken
>> years to collect reliable data from field samples and experiments in order
>> to make the model realistic. And that was with an artificially simplified
>> model system. I can't imagine what it would have taken to build a "real"
>> model.
>>
>> Even the climate modellers acknowledge that over the last decade, all
>> they've managed to do is confirm what their models CAN'T do (and likely
>> never will). Somebody should tell the IPCC that bit about models not
>> being predictive tools.
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