Definition of a species

To: David James <>, Mike Honeyman <>, "" <>, "" <>
Subject: Definition of a species
From: Nikolas Haass <>
Date: Fri, 25 Nov 2011 04:23:47 -0800 (PST)
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!)




To unsubscribe from this mailing list,
send the message:
(in the body of the message, with no Subject line)

To unsubscribe from this mailing list,
send the
(in the body of the message, with no Subject line)

To unsubscribe from this mailing list,
send the message:
(in the body of the message, with no Subject line)

<Prev in Thread] Current Thread [Next in Thread>

The University of NSW School of Computer and Engineering takes no responsibility for the contents of this archive. It is purely a compilation of material sent by many people to the birding-aus mailing list. It has not been checked for accuracy nor its content verified in any way. If you wish to get material removed from the archive or have other queries about the archive e-mail Andrew Taylor at this address: andrewt@cse.unsw.EDU.AU