[Taxacom] The 'reality' of species boundaries -- Once Again (UGHHH!)

[Stephen Thorpe]

>Nice dodge.  So, again I ask

Nice dodge! Answering a reply by asking the question again! Sure you're not a politician? :)
The answer to your question is that there isn't a (completely precise) answer to your question, but there doesn't have to be one! Naturally demarcated areas of land like Australia don't have perfectly precise boundaries either, but that doesn't stop them from being perfectly meaningful and useful features of objective reality! If I have a motto, it would be "context is everything" (not to be taken out of context! :), and the overall context here, as I see it, is about bioinformatics involving computers (databases) requiring more precision than actually exists in biological taxonomy. I say that species boundaries are natural and a little fuzzy. This makes them very different to generic boundaries, which are purely conventional/subjective, and possibly not suited to automation by computers?

>No, not the same form as my Centropyge example
Did I not just say that it WASN'T intended to be of the same form. Quoting my own view back to me as if it contradicts me, eh? Sure you're not a politician? :)

>How would we determine it, if we had perfect knowledge (following your bomb analogy, if we had a scanner that could analyze the building in 3D and show exactly where the bomb was)?  How would we know -- biologically, and without human subjectivity -- whether it represents a case of two species forming rare hybrids, or one species with two different geographically-based morphotypes?  Is it measured in probability that two given organisms would produce viable offspring?  Or is there some other objective, non-human, biologically-based metric?

If we knew all the relevant biological facts, we could model the situation and see in advance what the outcome would be given enough time. It certainly depends on a complex of factors, so there is no simple answer. But either there will be something keeping the species apart (except for rare hybrids) or not. It might have something to do with inherited habitat preferences, and/or genitalic differences leading to a low probability of fertilization, and/or ...

>Now, let's say that the broad allopatric populations all die out, leaving only the hybrid populations, such that 100% of individuals form hybrids. Are they now suddenly the same species, simply because the allopatric populations disappeared?
If that were to happen, the result would be unchanged! If they were distinct species before the allopatric populations disappeared (=they would never have lost that broad integrity had they not died out), then they are still distinct species, albeit extinct ones, after they disappear, because had they not gone extinct they would have maintained their integrity (apart from the few hybrids) ...

Stephen

________________________________________
From: Richard Pyle [deepreef at bishopmuseum.org]
Sent: Saturday, 12 September 2009 1:32 p.m.
To: Stephen Thorpe
Subject: RE: [Taxacom] The 'reality' of species boundaries -- Once Again (UGHHH!)

> [reply] so, statistics is all just human subjectivity, is it?
> Funny, I thought the whole idea of statistics was to reveal
> objective facts about the world! But wait ... how could I
> have been so stupid? You have to choose a significance level!
> So, statistics is all just human subjectivity after all ...

Nice dodge.  So, again I ask: at what proportion of hybridization does it
stop being hybridization (between two different species), and start being
freely inter-breeding morphotypes (within the same species)?  Is that
threshold established through "real", "natural" values that exist
independent of human subjectivity?

> [reply] yes, indeed! Unusually (for me!), I was not intending
> it to be an analogy! It wasn't intended to be an example of
> the same form as your Centropyge example, but rather just
> another illustration of the paramount importance to species
> concepts of reproductive integrity issues.

No, not the same form as my Centropyge example.  For it to be the same form,
then you would need a case where you have some geographic regions where ONLY
males existed and reproduced with each other, and produced fertile
offspring; and other geographic regions where ONLY females existed and
reproduced with each other, and produced fertile offspring; and a few places
where both males and females occurred together, and reproduced with each
other, and produced fertile offspring; then it would be a meaningful
comparison. Do you have such an example involveing different male/female or
juvenile/adult morphotypes?

> [reply] Aha! Now we are getting somewhere! No, it depends on
> the way things are at present, and in principle could be
> determined right now

How would we determine it, if we had perfect knowledge (following your bomb
analogy, if we had a scanner that could analyze the building in 3D and show
exactly where the bomb was)?  How would we know -- biologically, and without
human subjectivity -- whether it represents a case of two species forming
rare hybrids, or one species with two different geographically-based
morphotypes?  Is it measured in probability that two given organisms would
produce viable offspring?  Or is there some other objective, non-human,
biologically-based metric?

> [reply] change "retroactively become the same species" to
> "were in fact the same species all along", and change
> "retroactively become different species" to "were in fact
> different species all along", and I would agree! :)

But you said:
"If the Centropyge FREELY INTERBRED, then hybrids would take over the whole
range and the whole darn lot would become one. If you think that is (slowly)
happening (and you are correct), then they are the same species."  By use of
the words "(slowly) happening", you indicate it as a process, which requires
time.  Whether or not it slowly happens depends on factors independent of
the existing population of organisms.  In orther words, if you want to claim
that they "were in fact different species all along", then you are implying
that some attribute of the organisms *makes* them different species.  But in
the example I gave, the trend towards or away from hybridization depends on
external factors (I gave the example of climate change).  Thus, whether or
not they *are* species today would not in any way depend on existing
properties of the organisms (we already know they can freely given the
opportunity to do so), but would depend on external factors in the future
(like whether the proportion of exant organisms that create hynrids
increases).


Let me try to put it a different way:  Suppose the current situation is that
less than one percent of all individuals of either morphotype form hybrids
(i.e., the only place we find hybrids is at the narrow zone of overlap). And
letr's say that's low enough hybridization that we don't call them the same
species.

Now, let's say that the broad allopatric populations all die out, leaving
only the hybrid populations, such that 100% of individuals form hybrids.
Are they now suddenly the same species, simply because the allopatric
populations disappeared?

I'm trying to get you to tell me what property of the organisms underlies
the species boundary.

Aloha,
Rich