[Taxacom] Forgotting at the edge of miracles

John Grehan calabar.john at gmail.com
Sun Apr 26 13:09:19 CDT 2015


Rich

Thank you for the clarification of your general principles. I guess I
consider vicariance is the principal process responsible for
differentiation of related taxa occurring in different locations. I think
so because of my understanding of the biogeographic evidence. I could be
wrong of course, and maybe the other 90% of undocumented taxa will say
something different for them.


On understanding of evolutionary history and distribution – true we only
know what we know for what we know. But what if there is never consensus?
Do we just say that we are a long way from understanding? Maybe the
ultimate truth of the universe is more than we can ever encompass through
empirical evidence.


> Who in biogeography has made claims that we are close to fully
understanding it

“ strong convictions about historical mechanisms behind apparent modern
distribution patterns of organisms (and especially when those patterns are
correlated with inferred patterns of speciation) are wholly unwarranted
when they are based on largely incomplete knowledge of current distribution
patterns and evolutionary relationships of something like 10% of biota.”


I see your point of view regarding the potential influence on what we know,
but just because we don’t know anything about the undocumented species does
not necessarily mean that we are a long way from understanding. It just
means we are a long way from completing an understanding of the
undocumented species (or maybe not if someone finds a way to document them
faster. I guess my conviction is that I can argue with conviction about the
patterns that are known.

John Grehan

On Sun, Apr 26, 2015 at 11:07 AM, Richard Pyle <deepreef at bishopmuseum.org>
wrote:

> > Could you put a bit of meat on your characterization?
>
> A bit?  Sure.
>
> > What do you mean by a single 'model' that accounts for all distributions.
>
> Well, we have lots of proposed hypotheses about historical mechanisms to
> account for modern geographic distribution patterns of organisms.  Some
> (most?) of these hypotheses involve mechanisms that occur on evolutionary
> time scales (i.e., the implication being that present-day patterns of
> geographic occurrence of organisms reflects historical patterns of
> geographic speciation of organisms). Other hypotheses involve mechanisms
> that occur on ecological (i.e., sub-evolutionary) time-scales (the
> implication being that present-day patterns of geographic occurrence does
> not necessarily reflect historical patterns of speciation).  Good
> hypotheses show how existing evidence "fits" the proposed mechanism behind
> how populations of organisms got to be where they are now. Better
> hypotheses show how the existing evidence "fits" the proposed mechanism
> behind how populations of organisms got to be where they are now MORE
> EFFECTIVELY than alternative hypotheses (i.e., in many cases, the same
> evidence often "fits" multiple different competing hypotheses).  The BEST
> hypotheses make specific, testable predictions about future (but not yet
> acquired) evidence, in ways that support one hypothesis over others.
>
> This is all good -- exactly the sort of process by which science SHOULD
> progress (i.e., using empirical data to support or refute alternate
> competing hypotheses).
>
> Now, getting to your question, I used the word "model" as a more inclusive
> term of "mechanisms".  So, one "model" of biogeography, for example, is
> that organisms occur where they do now because historical vicariant events
> have shaped patterns of allopatry and subsequent speciation.  Another model
> of biogeography is that organisms occur where they do now because
> historical dispersal of organisms has shaped patterns of allopatry and
> subsequent speciation.  Other models involve mechanisms of extinction and
> re-colonization, or consequences of both organism-induced and Earth-induced
> factors, or various other sets of factors.
>
> I was echoing and extending Tony's complaint of "A presumption of
> dispersal as an explanation for everything makes for uninteresting, and
> ultimately irrelevant, research",  to replace the word "dispersal" with
> *any* mechanism that has been proposed to account for modern geographic
> distribution patterns of organisms; the key phrase being "as an explanation
> for everything".
>
> The point I was trying to make is that often-times combatants in these
> biogeopgraphic debates act as though there is necessarily one dominant
> mechanism to explain modern distribution patterns of most organisms, and
> the alternate mechanisms only apply to exceptional situations.  Maybe
> different mechanisms play greater or lesser roles for different kinds of
> organisms (e.g., coral-reef fishes vs. terrestrial mammals). Maybe in some
> cases, modern distribution patterns correlate well with historical patterns
> of speciation. Maybe in other cases, they don't.  My main point is that the
> word "Maybe" applies here because we are still "SO, SO, SO far away from
> understanding both evolutionary history and the actual distribution
> patterns of most living things".
>
> > And what is the basis for your contention that we are 'SO, SO' far away
> from understanding evolutionary history and distributions of living things.
>
> That's easy:
>
> 1) The most plausible estimates put total diversity at around 10-30
> million species. We've only cataloged about 2 million (let's call it 10%).
> We obviously don't know the distribution patterns of species that we don't
> even know exist yet. So, at BEST, the evidence to support alternative
> mechanisms behind patterns of speciation and biogeography are using only
> 10% of available evidence.
>
> 2) We are, of course, far from the "BEST" situation (i.e., 10%) because we
> have not yet confidently established evolutionary relationships among the
> 10% of organisms we do know about. For example, molecular evidence strongly
> supports a phylogeny of ((Humans, Chimps), Orangutans); yet you have shared
> with this list in the past compelling morphological and other non-molecular
> evidence to support a phylogeny of ((Humans, Orangutans), Chimps).  If the
> best we can say about one of the most well-studied examples of evolutionary
> relationships is, "we have conflicting evidence"; then where does that
> leave us with the rest of the 2 million species?
>
> 3) Even if we ignore our ignorance of evolutionary relationships, and
> simply trust our assessment of species boundaries to focus on inferring
> mechanisms of biogeography from observed distribution patterns (without
> trying to correlate to patterns of speciation), we are still woefully
> lacking in our documentation of the current distribution patterns of most
> of the known species (let alone the unknown species).
>
> > Who in biogeography has made claims that we are close to fully
> understanding it
>
> Well, we have these seemingly endless (and sometimes fierce) arguments
> about biogeography, and historical mechanisms to explain observed modern
> patterns of distribution. What are these arguments about, if not,
> fundamentally "Mechanism 'X' explains most distribution patterns better
> than mechanism 'Y'"?  My point (again, to echo Tony's), is that such strong
> convictions about historical mechanisms behind apparent modern distribution
> patterns of organisms (and especially when those patterns are correlated
> with inferred patterns of speciation) are wholly unwarranted when they are
> based on largely incomplete knowledge of current distribution patterns and
> evolutionary relationships of something like 10% of biota.
>
> I hope that addresses your questions.
>
> Aloha,
> Rich
>
>



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