Hi Nikolas,
Give me a break please. I didn't advocate a strict hybridisation rule to define
species. I only said that a study of hybridisation could resolve the
species/subspecies question for the lurida boobook owl in the Wet tropics
rainforests of North Queensland. You then corrected me by saying "You cannot
use hybridisation as a proof for subspecies versus species". You have since
refined that to say that hybridisation cannot be applied strictly
because 'valid' species of gulls and species of ducks hybridise. I agree with
entirely that these species hybridise, only with the caveat that 'valid
species' is a human concept based as much on fashion as on reality. But lets
work back to my original point through your example.
Gulls are colonial breeders that disperse widely and are as much nomadic as
migratory. Not so long ago in geological time they started radiating and
diverging. But now, due to global warming (historical) and the industrial
revolution these new forms are exploding in population size, expanding their
ranges, overcoming the isolation barriers thatr had them diverging, and coming
into secondary contact (i.e. meeting again the populations they were previously
isolated from). So they hybridise, not surprisingly. Taxonomists argue for a
SPECIAL case that hybridisation is not relevant to gulls at the moment. Fair
enough, although they now recognise certain species that inevitably, through
hybridisation, will not exist for too long. Its not extinction, its reverse
radiation.
lurida is entirely different and not part of this SPECIAL case. It is an owl
confined to the wet tropics rainforests. The species has a tiny range
(though large enough to support many endemic species) and is surrounded on all
sides (presently) by its nearest ancestor. It is isolated from other boobooks
only by rainforest habitat. Other boobooks occur in the same latitude,
longitude, altitude, terrain and climate. If it does not interbreed with other
forms of boobook on its door step it is genetically isolated and a full species
by any definition. If it does hybridise, them we have to consider how much and
why.
I don't say this based on what molecular taxonomists write about birds they've
never seen or what cladistic compute programs consider most probable. I have
spent well over a hundred nights spotlighting in NE Qld and I have seen lurida,
ocellata/boobook, presumed hybrids, and unidentified boobooks of a different
character altogether (possibly an undescribed taxon) on many occasions.
David James,
Sydney
==============================
________________________________
From: Nikolas Haass <>
To: David James <>; Mike Honeyman
<>; ""
<>; ""
<>
Sent: Friday, 25 November 2011 11:23 PM
Subject: Definition of a species
Hi David,
If you use hybridization as a strict indicator to rule out two species, then
there should be only one or a few Anas, one or a few Aythya, one ore a few
Larus... I could endlessly continue this list of genera containing accepted
species that hybridize naturally. ...and what about the famous "Swoose" (Mute
Swan X Greylag Goose)? Is Greylag Goose a subspecies of Mute Swan or vice versa?
BTW I'd like to correct a little error: I never said that hybridization ONLY
occurs between "two species nowadays". I said that hybridization ALSO occurs
between "two species nowadays"
Cheers,
Nikolas
----------------
Nikolas Haass
Sydney, NSW
________________________________
From: David James <>
To: Mike Honeyman <>; ""
<>; ""
<>
Sent: Friday, November 25, 2011 6:31 PM
Subject: Definition of a species
Species definitions are indeed a can of worms that have been discussed on B-A
many times, so I do not want to go there.
However, either I don't understand or don't agree with Nikolas and Mike about
hybridisation. A hybrid is simply the offspring of two different forms. The
parents can be individuals from two different genera, species, subspecies
(races), varieties, breeds or cultivars (but not morphs). It is not within the
domain (or interest) of taxonomy to redefine "hybridisation" as something that
only occurs between "two species nowadays".
Of course hybridisation can and is used to indicate species boundaries in ALL
species concepts. It is a line of evidence. When two forms are sympatric and it
is known that they don't hybridise everyone agrees that they are two species
(like the 2 white-tailed black-cockatoos). When they merge into each
other through hybridisation over a broad front then everyone agrees they are
one species (like green and yellow figbirds). In between there is lots of grey
and disagreement, but there is grey and disagreement in everything to do with
taxonomy. Taxonomists can still use hybridisation as a line of evidence
regardless of the species concept they follow, even if few do. There are at
least two big problems with using hybridisation: 1) to understand it you
need data from lots of individuals across a wide area; and 2) it is not
applicable to allopatric species. Neither is justification to dismiss it
as irrelevant to the process of speciation.
A frequent trend in taxonomy these days is to compare the percentage
differences in the Cytochrome B gene. Isn't this just looking for an indication
of whether two forms continue to share genes through the process of
hybridisation, or how long ago they stopped?
Lastly, nearly all existing checklists are predicated on lines of evidence
originally formed around concepts of speciation based on levels of
interbreeding (or the extrapolation of similar patterns when direct evididence
is lacking). Regardless of contemporary opinions, hybridisation still defines
the bird species painted in the field guides.
David James,
Sydney
==============================
________________________________
From: Mike Honeyman <>
To: ;
Sent: Thursday, 24 November 2011 10:03 PM
Subject: Definition of a species
I hear the sound of a can of worms being opened!
Simon there are many definitions of species, to suit specific 'species
concepts'. There are different species concepts that are preferred for
different phyla.
For birds the two most prevalent species concept are the Biological Species
Concept (BSC) after Mayr, and the Phylogenetic Species Concept (PSC) after
Cracraft.
BSC species = "groups of interbreeding populations reproductively isolated from
other such groups"
PSC species = "the smallest diagnosable cluster of organisms within which there
is a parental pattern of ancestry and descent"
Historically the BSC could use the ability to hybridise or not as an indicator
of species, but I think it's a while since anyone thought that was a reliable
indicator, as Nikolas has pointed out.
Re the owls. It is possible that the morphological differences are a red
herring - there could be an environmental 'switch' (e.g. the climate / habitats
that prevail in Tassie and NZ) that cause a particular morphology that exists
widely within the gene pool of the population to prevail. This could be tested
by moving Qld birds to Tassie and see what they look like after a couple of
generations (I've not looked at any of the papers by the way, just flying a
theoretical kite!)
Cheers
mjh
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