Re: Understanding MinEP and MaxEP
- From: "Perplexed in Peoria" <jimmenegay@xxxxxxxxxxxxx>
- Date: Thu, 15 Sep 2005 11:18:22 -0400 (EDT)
"William Morse" <wdmorse@xxxxxxxxxxxx> wrote in message news:dgaeug$a5f$1@xxxxxxxxxxxxxxxxxxxxxx
> Let me emphasize one more time that as I understand it Lotka did not
> think entropy was maximized - he thought the rate of work was maximized,
> which means the rate of entropy production is only about 50% of maximum -
> but is still not a minimum. How does this work in your example? Let us
> start with a system with some primary producers and look at the breakdown
> side (only because this is the side we are typically on - basically
> parasites on plants). Well, each organism wants to process resources at a
> high rate in order to outcompete other organisms, so there is necessary
> waste. But the waste creates other niches, since it represents
> unprocessed energy. Another organism appears to process that energy. But
> it also has competition, so it can't completely process it and creates
> its own waste. This creates another niche, and so on. The net result is
> effective conversion of potential energy to work (biomass) and entropy at
> close to the maximum rate of work conversion possible. If the rate is too
> high, then there is additional waste energy available to be converted to
> work (i.e. there is an available niche). If the rate is too low, some
> organism will be selected for that can more rapidly utilize the energy
> and will outcompete the existing occupier of the niche.
I agree with what you are saying both with regard to what Lotka's logic
was, and also with regard to the validity of that logic.
However you seem to be missing one key point which leads you to mistakenly
believe that there is a significant distinction between maximum work
and maximum entropy production. The thing you are missing is this:
In a 'climax' ecosystem at steady state, biomass does not accumulate!
Therefore, you can't use accumulation of biomass as a measure of 'work'.
Biomass may represent 'work' to a growing organism, but to an ecosystem
it is secondary production. Ultimately, all of the potential energy
available to the primary producers is going to be converted to heat.
(It may be converted to heat by either biological or non-biological
mechanisms, but it is going to become heat in any case). Now heat is
not the same as entropy - you have to divide heat by temperature to
get entropy. You get the most entropy if the heat production is done
at nice low biological temperatures (by leaves or termites) rather
than at high temperatures (black-body minerals or forest fires) from
the original potential energy source (sunlight or cellulose). So
maximum work really does come pretty close to maximum entropy production
if you count the 'work' as simply a secondary energy source.
Or are you saying that total biomass production (primary plus secondary
plus etc.) constitutes 'work'. Lotka likes ecosystems best when they
have many trophic levels? I am not sure that that idea is defensible.
To my mind, the ideal ecosystem would have a single species which
builds biomass in its youth, but lives off stored biomass in its
senescence, eventually withering away to nothing and leaving behind no
wastes. Other than its biochemical implausibility, what is wrong with
that? Would you count that as a particularly unproductive ecosystem?
I would say that as long as it consumes all of the available energy
resources and generates its heat at a low temperature, it is doing just
fine.
.
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