Proposal
(317) to South American
Classification Committee
Merge Buteo poecilochrous into B.
polyosoma
Effect on SACC: This
would merge Buteo
poecilochrous into B. polyosoma, and change common
name to Variable Hawk for this group.
Background & New information: This is a
case of a taxon that was described based upon a dubious diagnostic formula, one
that was never fully accepted but which nonetheless led some to believe there
must be differentiable characters in existence that merely awaited discovery
and elaboration. Following is a review of the description of the questionable
taxon, B. poecilochrous,
pointing out immediate problems with the original diagnosis. Subsequent to that
is a discussion of the salient features of the current taxonomic arguments.
Buteo poecilochrous was described by Gurney (1879) based upon wing length and body
size being greater than that in its closest relative, B. polyosoma; discussion of
geographic range for these two species was omitted. Stresemann (1925) later
suggested that relative lengths of primaries 6 and 8 (counting in the modern
way, inside out) be used to distinguish between polyosoma (p 8 > p 6) and poecilochrous (p 8 < p 6); later known as
"Stresemann's Wing Formula" for diagnosing the two species. Oddly,
and a foreshadowing of problems to come, the type specimen for poecilochrous has the wing
formula for polyosoma (holotype, adult, unknown sex; British
Museum of Natural History #8751330) (Hellmayr and Conover 1949: 91; Farquhar
1998). Although the geographic range of poecilochrous is entirely overlapped by that of polyosoma (Vaurie 1962), various authors have
suggested that polyosoma generally occurs at lower elevations
and that poecilochrous may be a high Andean endemic (Cabot
1991, Cabot and Serrano 1988, Fjeldså and Krabbe 1990).
Regardless of potential geographic
range or altitudinal segregation the essential feature in the purported
diagnosis of these taxa has rested exclusively on 'Stresemann's Wing Formula.'
I critically examined this diagnostic tool and found it to lack credibility
(Farquhar 1998). I demonstrated clinal variation in lengths of primaries as a
function of elevation (after statistically removing the effects of latitude and
longitude). I further showed that as wing length (p7) increases the relative
lengths of the primaries in question (p 6 and p 8) alternates from p 6 < p 8
in smaller birds (generally labeled as polyosoma)
to the reverse in larger birds (generally labeled as poecilochrous). The effect that
these alternating ratios has upon wing shape was also discussed and shown
graphically to produce, in wing tips with p 6 < p 8, a pointed wing tip
contour; and, in birds with p 6 > p 8 a wing tip contour that was more
rounded (p 5 also increases in length). This relationship clearly has an effect
on wing surface area for larger bodied birds (which typically have the rounded
wing tip). Lower elevation birds are smaller than those at higher elevations
and have more pointed wing tips compared to higher elevation birds, which are
larger and have more rounded wing tips. I showed this feature to be clinal and
does not provide any discernable boundaries in morphometric space with which to
separate taxa. I also examined vocalizations and immature plumage and found
both to lack evidence of segregation.
A recent paper (Cabot and de Vries
2003) discounted my work and argued if favor of a broad range of 13 to 19
(depending on the analysis they used) interrelated wing shape variables to
separate the taxa. Their arguments, both against my work and in favor of their
diagnosis, are weak on several levels (I'm preparing a response for
publication). It should, however, be pointed out that at in my conclusions
(Farquhar 1998: 41) "I suggest that polyosoma and poecilochrous be considered conspecific, at least until
further data are available to show that this taxonomic merger is
erroneous." Therefore, I welcome an unbiased and sensible revision that
clearly demonstrates a useful method for discriminating taxa from within this
group. I do not feel that Cabot and de Vries (2003) have done this. First, they
did not attempt to remove the confounding effects of latitude, longitude and
altitude on their set of morphometric variables that one must do to detect true
morphometric differences within a group that ranges from central Colombia to
Tierra del Fuego, and from 0 to 4500 masl. They present data (Cabot and de Vries
2003: Table 1) on factor loadings for a principal components analysis of 13
wing variables, and because all the significant loadings but one are on Factor
1 (generally referred to as the 'size' factor), one must suspect that there may
be age-related or geographic influences at play. They neither discussed this
problem nor attempted to rectify it. They stated (Cabot and de Vries 2003:203),
"In B. polyosoma body size is linked to geographical
features, such that bigger birds occur in the extreme south of the range.)."
Thus, they acknowledged geomorphological bias but did not control for it. I did
control for this bias by focusing on residuals of regressions of raw
morphometric variables against latitude, longitude and elevation, which allows
comparisons of measurements across such vast geographic distances in an
unbiased way. Perhaps a reanalysis of their data would show a different
picture, or perhaps not, but for now it is invalid. On this basis alone their
arguments for separating the taxa could be rejected.
Second, criticisms in Cabot and de Vries
(2003) of my work are weak.
(1) They make claims against my
finding that wing length and wing formula are clinal, and use multivariate
statistical techniques to show segregation. However, until they correct for
geomorphological biases their claims of discrete, species-level boundaries in
morphometric space are unsubstantiated. Further, in their set of standard
measurements of culmen, tarsus, toe and claw, in addition to numerous
measurements of the wing; nearly all (34 of 36) are shown to overlap in their
ranges of measurements between females of each taxon and males of each taxon
(Cabot and de Vries, 2003: Table 2). Even if the dataset they found to be most
useful (the 13 - 19 wing shape measurements) were to be valid in a statistical
sense, how would one actually identify them in the field? One would have to
rely on a subjective gestalt, or trap and measure every bird, which would not
be defensible from conservation policy perspective. Such cryptic species are
not unknown to science but this layer of uncertainty begs even more rigorous
quantitative underpinnings that at present elude us.
(2) They claim that plumage pattern
changes with age in adults. This is false. Beyond Farquhar (1998) there is
ample evidence (W. S. Clark, pers. comm..) that while there may be more than
one Basic plumage (as in B.
albicaudatus), the adult plumage -- characterized in part by presence of a
mostly white tail with a black-subterminal band -- retains its color pattern
throughout successive molts. Vaurie (1962) had advanced the notion that polyosoma and poecilochrous shared four plumages, with a fifth
belonging uniquely to polyosoma.
According to my analysis (Farquhar 1998), this is a highly polymorphic group
with at least 27 plumage types, most of which occur above 1,500m. There is no
consistent geographic, sexual or species-level variation here.
(3) They assert that I examined
only alarm calls, which in their opinion, "sometimes resemble those of
other Buteo species." Two points here. First, I
did not state that these were alarm calls, only that these vocalizations are
"often considered "alarm calls" and referenced an earlier paper
(Farquhar 1992) that discussed them more extensively. These are those
long-distance, 'species-typical' sounds emitted in a variety of contexts, including
alarm and territory defense. Second, these vocalizations are, in fact, quite
distinct from those in other taxa; there is some variation among purported poecilochrous and polyosoma,
but well within that found in B.
albicaudatus. Thus, there is no reliable way to distinguish taxa within
this group using these vocalizations. They did not counter my claim with data
of their own in their paper; if they have actual data to the contrary, they
need to present it for peer review.
(4) That I did not analyze other datasets
(e.g., ecological and behavioral) was due in part to the lack of such
information at the time of my work. However, the categories they list,
including predatory strategy and food selection, are highly dependent upon the
environment in which the birds are found, and these can be substantially
different across the vast range they occupy. Hence, the variation they describe
can easily be interpreted as local adaptation. The birds are opportunistic and
take prey based upon availability and conspicuousness, as far as I have seen in
the field, and in the literature. (5) Regarding breeding behavior, they state
that no polyandry has been observed in polyosoma, but is suspected in poecilochrous (the references they cite, Solis and Black
1981, and de Vries and Coello, unpubl. data, do not report genetic paternity
data). There are indeed numerous cases of 'polyosoma' having three
adults (trios, a female and two males) at a nest. In fact, one of de Vries' own
students worked on such a group in SW Ecuador, near Ancon, in the 1992-1993
time period. Moreover, the polyosoma on the Falkland Islands regularly have
trios at nests (J. Meiburg, pers. comm.).
Third, recent genetics work
(Riesing et al 2003) found no evidence that these two taxa should be separated
at the species level, as they "detected an average distance of 1.28%
between the subspecies polyosoma and poecilochrous in _CR1, whereas no genetic variability was
found in an unpublished cytb data set of 606 bp (C. Farquhar, pers.
comm.)." Cabot and de Vries (2003) did not mention this paper.
In summary, while it is not
inconceivable that more than one species level taxon (e.g., the Juan Fernandez
Hawk, B. polyosoma exsul,
or others) could exist within the B.
polyosoma/poecilochrous complex,
there is as yet no strong case for separating the taxa as polyosoma and poecilochrous at this time; the current data on
genetics, vocalizations, and morphometrics do not support it. As laid out in
Farquhar (1998), I suggest that, pending further data, Buteo poecilochrous be merged with Buteo polyosoma (Quoy and Gaimard 1824), which has
priority, and that Buteo polyosoma should be the scientific name for this
group (including one subspecies, the Juan Fernandez Hawk, B. polyosoma exsul); the common name
for all except the Juan Fernandez Hawk should be Variable Hawk. If 'buzzard' is
preferred over 'hawk' then this is acceptable.
References:
Cabot, J. 1991. Distribution and
habitat selection of Buteo
polyosoma and B. poecilochrous in Bolivia and neighbouring countries.
Bull. Brit. Ornithol. Club 111:199-209.
Cabot, J. and P. Serrano. 1988.
Distributional data of some non-passerine species in Bolivia. Bull. Brit. Orn.
Cl. 108:187-193.
Cabot, J. and T. de Vries. 2003. Buteo polyosoma and Buteo
poecilochrous are two distinct
species. Bull. Brit. Orn. Cl. 123:190-207.
Farquhar, C. C. 1992. Individual
and intersexual variation in alarm calls of the White-tailed Hawk. Condor 95:
234-239.
Farquhar, C. C. 1998. Buteo
polyosoma and B. poecilochrous, the
'Red-Backed Buzzards' of South America are conspecific. Condor 100:27-43.
Fjeldså, J., and N. Krabbe. 1990.
The birds of the high Andes. Zool. Mus., Univ. Copenhagen and Apollo Books,
Svendborg, Denmark.
Gurney, J. H. 1879. Note upon three
American raptorial birds apparently new to science. Ibis 3:171-178.
Hellmayr, C. E. and B. Conover.
1949. Catalogue of birds of the Americas. Field Mus. Nat. Hist., Zool. ser. 13,
pt. 1, no. 4.
Quoy, J. R. C., and J. P. Gaimard.
1824. In Voyage autour du monde, 1817-1820 (Par M. L. de Freycinet). Vol. 3:92.
Riesing MJ, Kruckenhauser L, Gamauf
A, Haring E. 2003. Molecular phylogeny of the genus Buteo (Aves: Accipitridae) based on
mitochondrial marker sequences. Molecular Phylogenetics and Evolution
27:328-342.
Solis, C and J. Black. 1981. Anidación
de Buteo poecilochrous en Antisana. Rev. Geogr., Quito.
21:132-142.
Stresemann, E. 1925.
Raubvogelstudien, X. Die weissschwänzigen Bussarde Süd-Amerikas. Jour. für
Ornith. 73:309-319.
Vaurie, C. 1962. A systematic study
of the Red-backed Hawks of South America. Condor 64:227-290.
Craig
Farquhar, November 2007
______________________________________________________________________________________________________
Comments from Laurent Raty: "I don't know who is right on the issue of
con/allospecificity of polyosoma and poecilochrous,
and will let this to Committee members. However, I feel quite
uncomfortable with the analytical methodology advocated by Craig Farquhar in
his 1998 paper (and again in the proposal), and would like to warn about this.
Attempting to control for a possible geomorphological bias is certainly
laudable in many situations but, in this particular case, it is potentially
more problematic than working with raw data. The method (pooling all the
individuals of two putative species, regressing their measurements against
latitude, longitude and elevation, then focusing on the residuals) rests on a
very strong assumption - namely, that latitude, longitude and
elevation affect the whole data set in one single and same way, independent
from the effect of possible taxonomic differences. If there really are two
species, this seems pretty unrealistic - particularly if these two species
are thought to have different elevational distributions, as in the present
case. If this assumption is violated, then it is basically impossible
to "remove a geomorphological bias" without affecting seriously
the taxonomy-related signal in the data, perhaps even destroying it
entirely. To take an extreme situation: in a data set pooling the measurements
of two morphologically discrete species that fully segregate
altitudinally, "controlling for an elevation bias" would be largely
equivalent to "controlling for species". In such a case, looking
for differences between the two species in the residuals, would be
looking for differences we have just actively erased from the data; it
would be no surprise if we don't find them... (I have attached a .xls file with a simulated example illustrating
the extent of the problem in this type of situation, in case it can help.)
There is much too high risk of false negative associated to this
method, and I do not think it should be interpreted as
showing conclusively an absence of morphological discreteness."
Comments from Robbins: "NO.
There are two important considerations to this proposal. Whether a Buteo that has been referred to as poecilochrous merits species
recognition, and if it does, what is the appropriate name? I have been uneasy
about the recognition of "poecilochrous" for a long time,
given the uncertainty of how one distinguishes it from polyosoma and how these two purportedly separate
out elevationally. Given L. Raty's comments about Farquhar's supposition, that
Cabot and de Vries (2003) analysis is fraught with compounding factors, I
consulted Cabot and de Vries's paper. Regardless of what the truth is, I found
the Cabot and de Vries paper to have many shortcomings; in fact, I was so
appalled at the lack of critical information (e.g., provenance of captive birds
from Peru), unsubstantiated statements, misstatements about natural history,
inappropriate references (some of which were missing from the References [e.g.,
Remsen and Traylor 1989]) that I wondered how the paper got published in that
state. The genetic data mentioned by Farquhar was also published in 2003, so
Cabot and de Vries would not have been aware of those data. Although Riesing et
al. (2003) suggest poecilochrous does not merit species status based on the
low genetic divergence from polyosoma,
I note that they had only a single example of
poecilochrous from
an imprecise locality ("Monte Antisana", Ecuador), and perhaps from
an unvouchered specimen. Frustratingly, the Cabot and de Vries study missed the
opportunity of examining genetic variation and definitively addressing this
question. Indeed, given that Stresemann's criterion for separating these two
purported taxa apparently is invalid, genetic data might be needed to ascertain
the identification of the holotype of poecilochrous.
"In summary, from what I can
ascertain, the question of the validity of poecilochrous is far from resolved. Given that most works
continue to treat poecilochrous as
a species, I presume the best course of action is to continue to recognize it
until there is a definitive data set that indicates otherwise. Hence, at this
point I vote "no" for merging poecilochrous into polyosoma."
Comments from Stiles: "NO.
Given that Farquhar's analysis has problems, as discussed by Raty, plus my
admittedly limited experience with both of these birds in Colombia where they
do separate out altitudinally and seem distinguishable morphologically (old
records of poecilochrous here being misidentifications) and
extensive discussions of the problem with Cabot and De Vries, who have studied
virtually all extant specimens, I do not think that current evidence indicates
anything but considering both as good species."
Comments from Zimmer: "NO.
This one is a mess! It seems as though neither side has made a particularly
convincing case. Given the questions regarding the statistical methodology used
by Farquhar, I would agree with Mark and Gary that we are best off sticking
with the status quo, even though it may be equally flawed."
Comments from William S. Clark: "I am in favor of Proposal 317. I believe
the Farquhar has made a strong case for this merger. I am familiar with both
taxa in the field and from museum skins. I consider them to be one species.
"There are no sound taxonomic reasons for considering them as
two species. The 'conservative' stance of accepting Dickinson (2003) as the
ground truth for the taxonomic list doesn't seem to make much sense in this
case, as there is no way to tell these two taxa apart, except for altitude, and
even that may be suspect, as birds can fly.
"The two taxa in question can't be distinguished by plumage
or by voice. The method given by Stresemann for distinguishing them has been
shown to be flawed by Farquhar. The small differences in DNA are no doubt due
to geographic isolation. The many responses by folks working on DNA taxonomy to
my questions about their taxonomic relationship resulted in a variety of
answers, so it is clear that DNA in itself will be little help in determining
whether they are one or two species.
"I agree with Robbins's comments on the lack of usefulness of
arguments presented by Cabot and de Vries (2003) for two species. I go further
and wonder why the reviewers didn't catch the numerous errors in this paper,
many of which were pointed out by Robbins.
"As there is no way to distinguish the two taxa for certain,
they should be considered as one species, unless and until someone comes up
with a way to distinguish them. One has to assume in light of their
similarities, that they would readily interbreed should then come into contact.
The problem is: how will we know when that will happen? Or if it hasn't already
happened?"
Comments from Jaramillo: "I
would vote an emphatic YES on this one. I do not see a way to support the
status quo of maintaining two species here given that there is no reliable way
of telling them apart. Stresemann's wing formula feature does not work, plumage
features do not separate them, average size and elevation are left over
perhaps? Perhaps poecilochrous is a good subspecies, but not a good species.
There is another issue here, mainly that this hawk has a clearly separable
highland and lowland population when you are in the north, such as Ecuador with
coastal polyosoma being diagnosable (according to those
who know them) from highland poecilochrous.
However such is not the case when you get to the south. The highland populations
and lowland populations are continuous in northern Chile and NW Argentina.
There is absolutely no way to tell where there is any discrete break between poecilochrous and polyosoma
here as far as I can tell. There are birds in the lowland valleys near sea level
in Arica, and birds which get up to 5000 m in elevation here, with populations
all the way in-between. In Putre at 3500 m these hawks are relatively common,
and seem no bigger or more eagle-like in shape than ones in the lowlands.
Higher up in the Altiplano, their abundance decreases and some I have convinced
myself are larger and broader-winged than birds from farther down, but this is
a tiny average difference, if it is real at all. I have not looked into the
specimens, but I doubt that there are that many from these areas where lowland
and highland populations are entirely linked. In any case my field experience
here is that there is no break, no barrier, no clear difference between
highland and lowland birds. Now another question to ask is where exactly is the
southernmost range for poecilochrous?
If this is a diagnosable taxon, there has to be an answer for this question. However,
"Variable Hawks" are common throughout the alpine zone from northern
Chile all the way to the south of the continent. It is common to see
"Variable Hawks" at 3000 m in the Santiago Andes, where many of the
local species show clear affinities with altiplano species, yet from all I have
been able to gather these highland populations have always been classed as polyosoma,
not poecilochrous. Indeed they
are inseparable from those in the Chilean/Patagonian lowland; in addition there
is absolutely no barrier between the highland populations here and those from
farther north. I have a hard time believing that in the Alpine zone as one
proceeds north from Santiago there is a magical spot where polyosoma becomes poecilochrous. Given how similar, or
nearly identical these forms are from a Chilean/Argentinean perspective, I have
absolutely no confidence that there would be any barrier to gene flow between these
entities, if they are real entities to begin with. As far as I am concerned
there is a greater likelihood that Thayer's Gull and Iceland Gulls are good
species versus this mess. I do think that maintaining these two as separate
species, or supporting the status quo makes little sense given the available
evidence. Sure there may be some problems with Farquhar's analysis, there are
also problems with Cabot's analysis. But from my perspective, and I am very
keen and interested in field identification challenges, there is no difference between
highland and lowland populations of this hawk in the southern cone.
"Not that this should
influence, but there was a point made that maintaining the status quo was
adequate as most folks treat these as two separate species. In our Birds of
Chile as well as Schulenberg et al.'s Birds of Peru, and Mazar Barnett and
Pearman's checklist of Argentine birds these two entities are lumped under polyosoma. So at least from a
Southern South American perspective there seems to be an acceptance to join
these two forms."
Comments from Remsen:
"YES. What a mess. I would say that the burden-of-proof is that these two
forms actually represent separate species. Looking at it broadly, especially
after Alvaro's comments, it appears to me that we could have nothing more than
a high- and low-elevation ecotype whose distinctions disappear toward the
south, where the gap between then disappears. Because the morphological
boundaries appear muddled (although part of that might be because the way the
data were analyzed, as pointed out by Laurent), I think that demonstration of
lack of gene flow is required to maintain these two as species. I am not aware
of any two species in the family that are this close in phenotype."
Comments from Stotz:
"YES. In general, I support sticking with the status quo until there is a
clear reason to make a change. In this case despite some lack of clarity,
I just can't support the status quo. Even if the alleged character is
valid, which I'd say is at best doubtful, do we really think that wing formula
is an adequate character to base species status on? Admittedly, in some
species, like Empidonax flycatchers or pewees, wing formula is used
to identify specimens, but that is not the basis for considering the species
involved as distinct. In this case, I don't think there is any clear plumage or
vocal characteristic that differentiate the two taxa, so why would we consider
them separate species? In Peru, much as Alvaro indicates for Chile, distinguishing
the two taxa is essentially impossible. You basically assume based on
elevation which species you have, but they are continuously distributed elevationally.
When I think of other hawks or falcons, I don't think of cases where you have
anything like the confusion as to what constitutes a valid species. There are
cryptic species in Micrastur,
but all have been differentiated by distinctive voices; there doesn't appear to
be vocal differences in polyosoma/poecilochrous.
"Finally, I should say that
while I understand the criticism of Raty (just think back to the study that
showed smooth clinal variation in morphometrics in Screech-Owl that went across
the species boundary between Eastern and Western Screech-Owl), the fact
is that if we are relying on differences in multivariate space to distinguish
the species there is a problem. Even if Farquhar's morphometric analysis
is flawed, the lack plumage and vocal differences between the two would seem to
me to sink a treatment of them as two species."
Comments from Pacheco:
"YES. Ainda que sem maior experiência com os
táxons implicados, estou inclinado a considerar o que criticamente disse
sobretudo Alvaro."
Comments from Nores: "YES para dar una respuesta, pero evidentemente es algo
difícil de decidir en base a los numerosos comentarios. En principio, yo diría
que poecilochrous es una subespecie más grande de polyosoma que vive a mayor altura. En el HBW Thiollay
insiste con que la pluma 3 es más larga que la 5 (de afuera a adentro) en polyosoma y más corta en poecilochrous, e incluso muestra un
esquema de ambas alas."
Comments from Cadena:
"YES, the arguments presented by Alvaro and Doug are compelling. I agree
that although the Farquhar study might have problems, there is no reason to
continue recognizing two species that cannot be told apart reliably by any
means."
Comments from Schulenberg:
"YES. Good lord, we've waited long enough to do away with Buteo poecilochrous.
“I’m not intimidated by the general
notion of taxa that can not be distinguished morphologically, or for which we
need multivariate statistics to help identify birds in the hand - I'm
interested in Scytalopus and tyrannids, after all. But in the cases
of those species, we at least have independent evidence (e.g., vocalizations)
that tell us clearly that we are dealing with more than one taxon, whether we
can distinguish them morphologically or not.
"In the case of these two Buteo, however, the arguments to
maintain poecilochrous smack of a post-hoc attempt to find
something, anything, by which to continue recognizing a taxon that I doubt
anyone would have noticed in the first place, were it not for the historical
accident that this name survived despite long-term and great reservations about
how to identify it. Absent a compelling argument that we have strong reasons to
think that there are two species-level taxa, reasons that I don't see in Cabot
and de Vries, then all this fiddling with a mass of measurements is beside the
point.
"So, I agree with those who
argue that, as Van put it, "the burden-of-proof is that these two forms
actually represent separate species." And to that end, I really don't want
to hear another word about wing tip formulas, multivariate statistics, or right
and wrong ways to control for variables, factors, etc. The clearest, and most
obvious, way to demonstrate that there are two species here would be to show a
marked genetic difference between the two. Although no study has tackled the
problem this way, two papers have touched on the issue. One is paper cited in
the proposal. Now we have a new paper (Lerner et al., 2008, Molecular
phylogenetics of the Buteonine birds of prey (Accipitridae), Auk 125: 304-315)
that also shows no genetic differentiation between poecilochrous and polyosoma.
I don't want to make too much of the results from Lerner et al., since there is
no real voucher for their poecilochrous,
but even so, that's zero for two on poecilochrous vs. polyosoma.
Are we getting a signal here?"
Additional comments from Craig
Farquhar:
"I wish to thank everyone for their insightful
comments and criticisms, and for the ultimate consensus being in favor of the
merger. As Tom pointed out there probably should never have been a split,
thereby precluding the ensuing snare of argumentation. This was indeed a messy situation,
as are many cases in alpha taxonomy, and while this one may be reopened pending
further rigorous study for now the case would appear closed. In the end, my
proposal served more as a catalyst for coalescing long-standing opposition to the
two-species notion. And had it not been for Alvaro's passionate and supportive
narrative I believe we'd still be arguing the case. Is there some way to cite
in future scientific publications not only the terminal decisions but also the
comments by the SACC reviewers, which in this case were invaluable? For this merger
it came down to a judgment call, which I guess defines the state of the art in
taxonomy no matter what the latest analytical tools dictate. Is this an
unbiased science? I'll reserve comment on that one. But it does take me back to
the arguments by the 17th century Nominalists, particularly John Locke, who
contended that species have "no objective reality." Alas, we are category-centric
beings so we must excuse ourselves despite ourselves.
"Having said all that, I would still like to take this
opportunity to address the issue raised by the first reviewer (Laurent Raty)
which served to perpetuate the notion (perhaps correct at some level) that analyses
in my 1998 Condor paper were flawed. It should be noted
that he found fault with but one of the several analyses I presented in my 1998
paper, that being the one used to generate Figure 2 (use of residuals to remove
geomorphological effects of latitude, longitude and altitude). I accepted the
assumption that the relationship between the morphometric and geographic
variables was linear, indeed it might not have been. I agree there is no
practical a-priori basis for making that assumption. But if one must make that
assumption then I would argue that parsimony should be the basis, such that exploring
all the multitudes of transformations and adjustments to the model would have only
served to complicate and perhaps invalidate the issue. I could have left that
analysis out based solely on the inability to satisfy the above assumption but
I retained it because it seemed appropriate for the following reasons. First,
the raw data used to generate Figure 4 clearly showed an elevational cline for
longest primary. Thus the 'extreme' dataset offered by Raty showing two very
divergent groups subsequently converging under analysis of residuals is not
strictly comparable here. The two former taxa were shown by my analysis to broadly
overlap in wing length. Contrary to Raty's statement these birds also broadly
overlap in distribution elevationally (see also Jaramillo's comments). Second,
knowing the cline existed it was safe to speculate that for at least that
morphometric variable (p7) there was no basis for separating taxa (wing length
had been considered one of the main diagnostic criteria in separating the two
putative taxa). I thought it appropriate to also look at residuals (in
retrospect I should have presented the raw data first...) to see how the
morphometric and geographic variables related, statistically free of a
geomorphological effect -- perhaps one not revealed by simply looking at raw p7
vs. altitude (Fig. 4). In my opinion, one would want to remove such a bias in
closely related groups to control for local adaptation. If no divergence were
apparent from such an analysis one could at least tentatively conclude the
geographic variables were not influencing the morphometric variables (assuming
the relationship in this case is linear). In contrast, if divergence did
present itself then this might be a stronger case that locally adapted traits
might be evidence for evolutionary divergence. Of course, one would need to
look at the fitness of the trait in question and its heritability before
determining its use in rendering taxonomic decisions. Local adaptation due
simply to geography could cloud taxonomic boundaries, I think we can all agree on
that. Therefore, Raty's warning about the use of Figure 2 analysis is not
entirely relevant in this case.
"In short, my residuals analysis was but one facet of the
overall methodology and I find it unfortunate that many of the reviewers
focused only on that angle, and Raty's comments, perhaps not having actually read
the entire paper. If it would satisfy the majority to disregard the residuals
analysis I would be comfortable with that. I think the rest of the paper is
strong enough to make the case that the original diagnostic tools were
ineffective resulting in collapsing the boundary between the two taxa. I, like
Tom, eschew overly statistical examinations of species level taxonomy as these
tend to be impossible to relate to in the real world. This is exactly why I
used the very low-tech method of examining wing tip contour (i.e., Stresemann's
blasted wing formula) by overlaying raw data for lengths of p5 through p9 (Fig
3) which nicely shows how the wing tip changes from 'pointed' in small birds to
more 'rounded' in larger birds in both adults and immatures. Clearly, we are
looking at a clinal wing aspect ratio phenomenon most likely associated with body
size and the need for more wing surface area to maintain powered flight in
heavier birds. The genetic data, although somewhat incomplete, published after
my paper evidently also do not support a polyosoma/poecilochrous split.
"Thanks again to all who engaged in this lively and fruitful
discussion and if further comments and suggestions develop I would welcome them
(perhaps in private email, if necessary, to avoid cluttering this forum)."