Definition of a species

To: Nikolas Haass <>, Mike Honeyman <>, "" <>, "" <>
Subject: Definition of a species
From: David James <>
Date: Sat, 26 Nov 2011 01:33:01 -0800 (PST)
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 
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 
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, 


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"



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, 


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 

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!)




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