[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Long, long last gasp.



accidentally sent this only to John Bois...

> John Bois (jbois@umd5.umd.edu) wrote:
> 
> <OK.  So what do you call it?  For sake of argument, assume that zebra
> mussel populations thrive because other mussels are limited by
> predation.
> This allows zebra mussels to take all the resources--including
> substrate--from the native mussels.  Is this predation or competition.>
> 
>   Capitalization. They are taking advantage of a situation they do not
> actually have a part in. As such happens during several faunal
> interchanges, opportunity to exapt new territory or food availability,
> even when they did not slam the land masses together to acheive that
> effect, still permits the organisms their availabilities; still, they
> may
> not survive the interchange, and can easily be knocked out by unrelated
> events to competition. An absence of a predator species can lead to a
> vacuum that must be filled; other species expand to compensate. There
> still is not species to fill in the role the American cheetah played,
> but
> that seems null because of the expansion of the wolf to hunt deer and
> antelope in America which the cheetah likely did. Does not mean the wolf
> outcompeted and caused the death of the cheetah. Despite access, wolves
> do
> not hunt in Africa, and this may be reflective of recent competitive
> forces, though those forces (cheetahs, leopards, likely the Asiatic
> lion)
> do not appear to be in abundance.
> 
> <Surely, the zebra mussels are currently outcompeting local species.>
> 
>   If they're better at feeding on a food source, or attracting it, and
> thereby overtly preventing other species from food, or occuring at spots
> where food would be retained more easily and thereby prevent flow into
> other species, sure. But not so given examples where food is evenly
> available. Given even access, different species should only be limited
> by
> their own abilities, and thus competition can occur. Given lack of
> ability
> to prevent another species from capitalizing on a food source, does not
> mean that species is "out competing" anything; it just lacks the ability
> to capitalize and risks death. Thus, mutation. If some population
> manages
> to develop a physical or geographical "upper hand," and unless that
> population prevents another predator from attaining the same goal by
> overt
> action (like, the rainforest biome, where competition among tree species
> for light often leads to stunted or dying growth, lack of undergrowth,
> grasses, etc.), then competition is not the means of success, its
> capitalization. Lions and hyenas compete, since they actively hunt one
> another to prevent the other's success and for the most part the same
> foods. Classic example. On the otherhand, zebra mussels do nothing to
> prevent the other species ability to function, and cannot actively
> compete; they merely capitalize on opportunity, as given the example
> John
> gave.
> 
> <Practically _all_ niche delineations of today are assumed to have been
> the result of unobservable "ghost" competition.  If we can't observe it
> even in extant species, how can we ever observe it in extinct species. 
> This is an unrealistic expectation.  Yet, this doesn't reduce its
> likelihood.>
> 
>   If we do not observe it, how can we in any reasonable frame of mine
> assume it could happen at all? It's a possibility, but one not easily
> favorable, as you say. Yet you say. Competition of species would require
> extensive ecological sampling well below the million-year-markers
> available, and layer by layer, bonebed by bonebed show that one species
> was knocking the other off the face of the Earth. Show where this has
> happened, been proven, and not a pipe dream. Of all the possibilities
> why,
> why favor competition to knock out the pterosaurs? Obviously the
> bird/ptero argument is a neat one, since there is _some_ support for it,
> but it is an ill-favored argument that would have it so that both
> species
> knocked _each other_ off the face of the Earth, one less adaptable to
> survival I must immediately argue against it for the lack of a viability
> that could ever occur. Only humans, in our infinite stupidity thanks to
> our ability to act against nature, can kill off our own species. Others
> seek to permit and endorse survival.
>  
> <No. My hypothesis is that both were reduced by a third group:
> neornithines(sp?).>
> 
>   Ah, one still ill-favored to experience. The evidence for this, or
> even
> to formulate the hypothesis, is based on what?
> 
> <Yes.  But also by past competitive interactions, i.e., niche
> partitioning.>
> 
>   Natural partitioning can occur through geographical means, as much as
> species competition, and unrelated natural means, as in metabolic
> features
> reducing populations at the poles, not that the species there prevent
> others from invading. Other species just can't cope with the weather and
> cold, and as such stay away; this favors the "competition with Gaia"
> idea,
> that the Earth is a proving ground, so that all species are in
> competition
> with the Earth's "design." A good example is that Wallace's Line is
> simply
> not crossed much at all, not that the birds or lizards or fish there are
> being prevented; they just DON'T.
> 
> <Yes.  But there was most likely niche partitioning (or geograhical>
> isolation) among the ratites themselves.>
> 
>   That each appears to be geographically isolated from the others, or
> that
> tinamous are smaller and flight-capable than rheas, and that cassowaries
> prefer denser territory than sympatric emus, yes. Kiwis favored smaller
> size, but may not at all be the "shruken" moa of some thought. They eat
> a
> diet of grubs, and are essentially predartory, whereas the extinct moa
> species have largely been shown to be herbivores, partitions by body
> weight, geography (valley to valley, some species of insects are known
> to
> diversity and becoming parapatric without competing, but simply by
> monopolizing a "chance" diversity not previously exploited by a similar
> insect), or specialization, by whatever [unobservable] means.
> Competition
> is one, largely unprovable, means; capitalization, usually in a vacuum,
> is
> another, more easily testable means.
> 
> 
> =====
> Jaime A. Headden
> 
>   Little steps are often the hardest to take.  We are too used to making
> leaps in the face of adversity, that a simple skip is so hard to do.  We
> should all learn to walk soft, walk small, see the world around us
> rather than zoom by it.
> 
> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
> 
> __________________________________
> Do you Yahoo!?
> Yahoo! SiteBuilder - Free web site building tool. Try it!
> http://webhosting.yahoo.com/ps/sb/
> 


=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free web site building tool. Try it!
http://webhosting.yahoo.com/ps/sb/