Proposal (96) to South American Classification
Committee
Split Embernagra
olivascens from E. platensis
[This proposal is based on the following
publication:
Hayes, F. E. 2003. Geographic variation in the
Great Pampa-Finch Embernagra platensis complex: evidence for two
species. Ardeola 50:223-235.]
The Great Pampa-Finch (Embernagra platensis)
of southern South America is represented by four subspecies belonging to two
distinct groups occurring in allopatry: (1) nominate E. p. platensis in
the east; and (2) E. p. olivascens, E. p. gossei, and
E. p. catamarcanus in the west. I propose splitting E. platensis
into two species: the monotypic Great Pampa-Finch, E. platensis,
and the polytypic Olive Pampa-Finch, E. olivascens. The two groups
approach each other closely in central Bolivia, western Paraguay, and central
Argentina, but do not overlap (see Fig. 1 in paper). Intergradation between the
two groups has been assumed by previous authors but never adequately
demonstrated.
The olivascens group differs from platensis
by the following six traits:
* averaging larger
in size
* having a
more strongly curved beak
* having a
deeper orange beak
* having less
extensive dusky colouration on the upper bill which is shaped differently
* lacking streaks
or only faintly streaked on the back
* having a
paler loral region, chin and abdomen.
Much overlap occurs in body size and shape, and
even plumage (considerable variability in wear complicates any plumage
analysis), but I found that the structure and coloration of the bill are the
most diagnostic characters (see Fig. 2 in paper). To quantitatively assess the
pattern of coloration on the bill, I measured the maximum height of pale
coloration on the side of the bill. There was slight overlap among taxa in this
measurement, but ALL specimens (including those misidentified, misplaced with
the wrong taxon, or with questionable locality data) were unambiguously
diagnosed to taxon based on the structure and pattern of coloration of the
bill. No individual, including those in which the measurements overlapped,
possessed intermediate traits.
The absence of clinal variation in the extent of
pale bill coloration within each form (see Table 3 in paper) demonstrates that
intergradation either does not occur or is potentially restricted to a narrow,
still undiscovered contact zone in central Bolivia, western Paraguay, or
north-central Argentina. Their apparent lack of sympatry could be attributable
to competitive exclusion. Given the likelihood that bill structure and color,
combined with other traits, may represent reproductive isolating mechanisms
between the two groups, they could be considered specifically distinct. Further
studies of vocalizations and genetics would be useful.
Floyd E. Hayes, February
2004
======================================================
Comments from Robbins: "NO. Although
Hayes may prove to be correct, the lack of any vocal or molecular analyses
leaves in my mind a question on whether platensis and olivascens deserve
species status. Even Hayes seems uncertain on whether these two should be
recognized as species when he states, 'I tentatively propose the
recognition....'. If he is tentative then I see no reason why we should support
the split until there is more information."
Comments from Zimmer: "NO. I'm with
Mark on this on. The evidence sounds flimsy at best, and is lacking any
information on voice. I see no reason to rush here, especially when Floyd also
appears tentative."
Comments from Remsen: "YES. Although
Floyd doesn't have all the pieces we normally require for allopatric taxa, he
does have what I consider to be the only important one for parapatric taxa,
those with a reasonable chance to exhibit free flow of genes, namely parapatry
(or even perhaps sympatry in this case) without any sign of intermediacy where
the two taxa come together. For me, this trumps any other indirect
information."
Comments from Stiles: "NO. The evidence
is suggestive but in my opinion not conclusive, in part because the
demonstration of "true" parapatry is not wholly convincing. The
closest approach shown by specimens of the two putative species seems to be on
the order of 100-300 km if I read the paper aright, and a lot could happen in that
distance! I think that field work in the possible contact zones would be
critical here, with use of vocalizations, morphometrics of specimens and if
possible genetic evidence. In the absence of such information, I feel that this
split is premature."
Comments from Nores: "NO. Pienso que las diferencias morfol—gicas no son demasiado importantes como
para considerarlas especies diferentes. Aunque esto no aclara demasiado, vale
la pena comentar que las dos subespecies se superponen (overlap) en Ucacha (C—rdoba,
Argentina) (Nores e Yzurieta 1980. Aves de ambientes acu‡ticos de C—rdoba y
centro de Argentina. Secr. Agr. Gan. Cba.)."
Comments from Jaramillo: "YES. I am
convinced by Floyd's data that there is little or no intergradation between
these two forms. Having a good deal of experience with the two groups, I have
always thought they were rather different beasts and had in my mind that it was
likely that two species were involved. Apart from the bill and plumage
differences, the voices of the two do differ, although I don't know how useful
that is in an oscine such as this. Furthermore, the habitats they take are
quite different. Both are in open areas, but platensis is found in marsh, marsh
edge, Pampas Grass thickets and other grass/reed dominated habitats. The olivascens group
takes drier habitats, sometimes with Pampas Grass and open grassy areas but
practically always with a dense shrub component. One point I would like
to make is that it disturbs me somewhat that what I am hearing from members is
that molecular or voice data is now a 'must' for convincing that a split is
warranted. Floyd's analysis is a traditional one, I hope that is not the
problem. I can see concerns about needing more information from the potential
area of contact and so forth, but that is an entirely different issue than
suggesting that having voice and molecular data is some kind of a requirement
for work like this to have weight. I would like to ask what voice data would
really do in a situation such as this one where you have two allopatric oscine
taxa, that have diverged enough to show structural and plumage differences.
Wouldn't you just expect voice to differ in this situation? What would it be
telling you that the data that Floyd has put forth not tell you? It is a very
different situation than dealing with suboscines and various non Passerines,
where we have good evidence that voice is hard-wired."