Re: Life's complexity: self-organization, evolution or both?

On Sat, 22 Sep 2007 01:28:15 GMT, Bill Morse
<wdNOSPAmorse@xxxxxxxxxxxxxxxx> wrote:

r norman wrote:

On Wed, 19 Sep 2007 23:30:35 GMT, Bill Morse
<wdNOSPAmorse@xxxxxxxxxxxxxxxx> wrote:

r norman wrote:

On Tue, 18 Sep 2007 02:22:08 GMT, John Harshman
<jharshman.diespamdie@xxxxxxxxxxx> wrote:

Bill Morse wrote:

r norman wrote:


On Mon, 17 Sep 2007 03:03:43 GMT, Bill Morse
<wdNOSPAmorse@xxxxxxxxxxxxxxxx> wrote:


Perplexed in Peoria wrote:



(snip)


That may well be true, but organism complexity and ecosystem
complexity are completely different animals. NS (i.e. reproduction
and genetic inheritance) is central in explaining organism
complexity. But NS isn't much involved in explaining ecosystem
complexity.

Arguable. One doesn't ordinarily think of ecosystems as having excess
reproduction. But they might be considered to have heritable fitness.
I don't think one should completely dismiss the idea of ecosystems
competing.


Ecosystems are MUCH simpler than organisms, and their evolution is
something even a physicist can understand.

This seems extraordinarily unlikely on the face of it. Ecosystems are
composed of a large number of organisms. All our experience with
other systems tells us that aggregations of large numbers of subunits
results in greater complexity than that exhibited by any of the
subunits.

It depends on how you count "number of subunits". Also, the patterns
of interaction between units within an organism are quite intense
whereas those between units within an ecosystem are rather weaker.
Yes, if somebody catches and eats you, that might be considered
intense from your point of view. But you have to look at the
population and the probability of being eaten. The nervous and
hormonal control systems, not to mention the genetic regulatory
control systems, within an organism and within a cell are much more
deterministic.


While I grant that there is a difference in intensity of interaction,
the definition is not all that clear. How does one treat
endosymbionts? Are they part of the larger organism or are they and
the larger organism part of a mini-ecosystem? And how does one treat
eusocial insects, remembering that ants comprise a huge fraction of
the organisms in many terrestrial ecosystems?

My initial thought in support of Pip's idea that ecosystems might be
simpler than organisms was that organisms in ecosystems might behave
statistically - I think this is in line with your argument that
interactions between units within an ecosystem are relatively weak.
But in reflecting on real ecosystems, I just don't see that
statistical methods capture much of what goes on. For instance,I'm
unaware of any statistical treatment that captures the importance of
capstone species.



But without trying to measure complexity to see which one "wins", you
must consider that organisms must contribute to the success of the
ecosystem in which they live if they are to survive and reproduce. So
yes, indeed, ecosystems are strongly affected by evolution and change
with evolution. So why not just say that they evolve, even though the
mechanism is rather different from evolution of populations and
species.


I can agree with that. But I am interested in the question of whether
ecosystems also evolve by a mechanism that is similar to natural
selection. Do ecosystems compete? In the classic view of the 1960's
that I was taught, there was for instance a natural succession of
ecosystems following a disturbance. I doubt this is the current
thinking. It seems to me instead that succession as well as such
phenomena as change in vegetation mix with altitude on a given
mountain can best be explained by a model of competition between
ecosystems.

I am attempting to disagree with both John and Richard simultaneously (no
mean feat in itself!), so I followed to this one because it contained both
of your comments.

That made no sense to me unless your last word was intended to be
"individuals" instead of "ecosystems". All succession would be is the
ability of different organisms to outcompete others in particular
environments over particular time scales, remembering that individuals
help create each others' environments. Succession is the statistical
result of all manner of individual interactions among species adapted to
different environmental features.

Yes, I agree with John. Succession is, indeed, still taught because
it occurs and can be readily observed. The reason for succession is
that the activity of organisms within an ecosystem cause significant
changes to the physical environment, that is to the ecosystem, to
their own detriment. Succession is, indeed, an "evolution" of
ecosystems using that word not in the biological sense but as the
playing out of a series of sequential events. The change is the
result of the ability of species and individuals within those species
to compete and survive in ever changing environments.

It seems my hazy memory of my ecology courses led me to confuse succession
with the concept of ecological communities - for some reason I had
thought that succession was marked by the same sort of shift in species
assemblages that is seen in change in vegetation with altitude.

I was not entirely mistaken, however -there are many recognized ecological
communities (e.g. beech-maple forest vs. oak pine forest), and in fact
some of these exhibit sharp boundaries. Kevin Kelly mentions "the
demarcation between the high tide seaweed community and the watery edge of
the spruce forest is an extreme no-man's-land of barren beach. One can
stand on this yard-wide strip of salty desert and sense the two
superorganisms on either side, fidgeting in their separate lives. As
another example, the border between deciduous forest and wildflower
prairie in the midwest is remarkably impermeable." An example I am more
familiar with is the transition in the Adirondacks from the mountain
conifer forest to the "krummholtz", or cripplebrush, and slightly above
that the treeline and transition to Alpine vegetation. The transitions at
lower elevations (e.g. from northern hardwood to hardwood conifer) creep
up on you as you hike up - you can sense a change but there are still many
members of the species assemblage of the lower elevation community. But
the latter two transitions are very sudden.

Now obviously the change is due to "the ability of different organisms to
outcompete others in particular environments." But in some of these
communities, the interactions between different organisms, the individuals
helping "create each others' environments", becomes a tight enough loop
that the whole community does behave in some sense as a superorganism. And
in those cases, I think the appropriate level to look at for explanations
is the ecosystem level, not the individual level.

Your memory is partly correct: succession is the succession of
ecological communities. However in reality you seldom see one
community totally replacing another distinct community. You
ordinarily see a gradual change is first a few isolated individuals
from the new community appear, then grow in number, then more of a
different species appear and grow in number. Sometimes there is a
cumulative effect which results in exponential growth of the new
members at the expense of the old so that, at the end, it looks like a
landslide. But it was many slow and gradual years in the making until
the final rush. For example, in so-called secondary succession, you
clear land (an abandoned empty lot or plowed field) but leave soil.
Then you get weeds growing, where 'weeds' are just pioneer species
characterized by r-selection: rapid growth to reproduction, small
size at maturity, production of tremendous number of offspring
(seeds) of small size and hence with few nutrients to support the next
generation, etc. Some more long-lasting (biennial and perennial vs.
annual) herbaceous species like grasses. Then the woody plants start
to invade. They have a difficult time starting because they often
tend to K-selection: slow growth, long time to maturity, production of
offspring (seeds) that are large and nutrient filled but small in
number. Their slow growth means the rapidly growing existing
population gets all the nutrients. But once they start, they outgrow
the herbaceous plants especially because, in succeeding years, they
start with a substantial above ground woody structure. Hence the
herbaceous pioneers get shaded out and lose the race except for those
that can sprout, grow to maturity, flower, and set seed all in the
time before the woody plants covering them have had a chance to fully
leaf out. That explains all our early spring flowers! The woody
plants start with small shrubs but these get shadowed out by taller
trees. There are difference between trees in longetivity, ability to
grow in shade, etc. so there is a succession even in tree species
until you have a mature climax forest. At least that is what happens
in my neck of the temperate zone woods. But it most definitely is not
an abrupt change of first this group of organisms, then that one, then
the last one.

You are mistaken about the altitudinal variation. That you are
confusing with latitudinal variation, both caused by temperature. At
the Sonora Desert Museum in Tucson Arizona there is a display of what
you see from the low altitude sonoran desert up through elevation to
and past the tree line at 10,000 foot elevation (Mt. Lemmon just
outside Tucson). That corresponds with moving Northward from the
desert through chaparral and grassland to deciduous forest, then
coniferous forest until you get past the tree line in the Arctic.
(Well, maybe you don't get that good Alpine tundra in southern
Arizona, but you certainly find it in Colorado and even at the
equation in Ecuador!

I don't see why you claim I am confusing altitudinal variation with
latitudinal variation, when you then go on to cite altitudinal variation
observed at Mt. Lemmon. Yes much of altitudinal variation recapitulates
latitudinal variation, although not completely since latitudinal variation
also includes the effects of seasonality. The point is still that one sees
different ecological communities with change in either latitude or
altitude, and that some of these transitions are abrupt.


As to places with abrupt changes, perhaps the best place to look is at
the seashore with its rather spectacular zonation depending on how
high the highest tide reaches, how low the lowest low tide falls, how
far the wave splash zone reaches, etc. Yes, there are community
interactions that produce positive feedback effects within
communities and negative feedback between them resulting in an abrupt
transition. But still, when you look at what is happening at the
boundary, it is individuals who live and die in particular
environments, not ecosystems competing one with another.

I guess I fail to see the distinction. Ecosystems are composed of individual
organisms. If the interactions between the individuals are significant
enough - if the environment experienced by an organism becomes determined
more by the other organisms present than by other environmental factors -
then one will see edges between ecosystems. Does this constitute
competition between the ecosystems? I am arguing that it does, that the
location of the edge is based on where one ecosystem becomes more
successful than another.

You might as well become all Gouldian while you are at it if you
insist on multiple levels of selection in those terms. And you are
very perilously close to the travails of 'group selection' with all
the problems that imposes. Yes there are people who advocate such
things, but nowadays they tend to be very careful about how they talk
about it and then they choose to talk only to known members of the
cabal.

I don't think my argument has much to do with group selection, at least in
the form advocated by Wynne-Edwards. As I said way back in the beginning of
this discussion, ecosystems don't have excess reproduction, which
eliminates any type of Darwinian selection. But some ecological communities
do exhibit feedback control, which following Odum lets them act as
systems, and as such these systems can compete for resources.

I read your original statement incorrectly and I hereby offer my
sincere apologies. You wrote "It seems my hazy memory of my ecology
courses led me to confuse succession with the concept of ecological
communities - for some reason I had thought that succession was marked
by the same sort of shift in species assemblages that is seen in
change in vegetation with altitude." I hastily read it to think that
you were still confusing succession with altitudinal variation and, in
my long-winded professorial mode, I described first succession and
then the altitude/latitude situation to contrast them. Definitely,
altitude correlates with latitude and definitely succession is a very
different thing.

As to whether the ecosystem is an 'entity' that can act as an
agent--- I guess I am taking the devil's advocate position here
espoused by others to say that the only real objects living and
breathing and interacting and competing are organisms (although
sometimes you can't even define 'organism'!). As a complex systems
and emergent properties devotee (though not as strong a one as dkomo
might like), I do believe that there is something in the systems
approach. However, when you look at the mechanistic details, it
always comes down to organisms. The ecosystem is, indeed, a system
and it has behavior and properties as a whole, properties I would call
emergent to the intense displeasure of some here. However I am still
not convinced that one ecosystem, acting as an agent, competes with
another. Grasses can suck up all the surface water and nutrients and
cover the ground densely to shut out the possibility of woody plants
taking root and slowly growing. On the other hand, woody plants shade
out the sub-canopy level and insulate it from the wind so that
low-growing herbaceous plants that rely on rapid growth and wind
pollination and dispersal are eliminated. I don't see that it is
necessary to say that grasslands compete against forests. An arid
area ecosystem works as a unit so that transpiration provides the
moisture to permit enough rain to water the plants. Remove the plants
and desertification follows -- no more plants = no more transpiration
and no more rain which means no more plants. The ecosystem as a whole
is a positive feedback bistable system. That is useful. Saying that
it competes is probably not.





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Relevant Pages

  • Re: Lifes complexity: self-organization, evolution or both?
    ... I don't think one should completely dismiss the idea of ecosystems ... composed of a large number of organisms. ... It seems to me instead that succession as well as such ... communities, ...
    (talk.origins)
  • Re: Lifes complexity: self-organization, evolution or both?
    ... One doesn't ordinarily think of ecosystems as having excess ... composed of a large number of organisms. ... there was for instance a natural succession of ecosystems ... assemblage of the lower elevation community. ...
    (talk.origins)
  • Re: Lifes complexity: self-organization, evolution or both?
    ... One doesn't ordinarily think of ecosystems as having ... are composed of a large number of organisms. ... succession of ecosystems following a disturbance. ... "the demarcation between the high tide seaweed community and the watery ...
    (talk.origins)
  • Re: Lifes complexity: self-organization, evolution or both?
    ... One doesn't ordinarily think of ecosystems as having excess ... composed of a large number of organisms. ... there was for instance a natural succession of ecosystems ... help create each others' environments. ...
    (talk.origins)
  • Re: Lifes complexity: self-organization, evolution or both?
    ... I don't think one should completely dismiss the idea of ecosystems ... composed of a large number of organisms. ... statistical treatment that captures the importance of capstone species. ... with the concept of ecological communities - for some reason I had ...
    (talk.origins)