birding-aus

Definition of a species

To: Birding-aus Aus <>
Subject: Definition of a species
From: Chris Charles <>
Date: Sat, 26 Nov 2011 22:18:57 +1100
Thanks for sharing this thread guys.
Thanks for sharing the knowledge.
I never thought of taxonomy as exciting before.

Chris

Chris Charles
0412 911 184

33deg 47'30"S
151deg10'09"E





On 26/11/2011, at 9:24 PM, Nikolas Haass wrote:

Thanks David,

I totally agree. Looks like there was some misunderstanding of each others comments...

The lurida story is indeed very interesting!

Cheers,

Nikolas


----------------
Nikolas Haass

Sydney, NSW


________________________________
 From: David James <>
To: Nikolas Haass <>; Mike Honeyman <>; "" <>; "" <birding- >
Sent: Saturday, November 26, 2011 8:33 PM
Subject: Re: [Birding-Aus] Definition of a species


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 <>; "" <>; "" <birding- >
Sent: Friday, 25 November 2011 11:23 PM
Subject: Re: [Birding-Aus] 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 <>; "" <>; "birding- " <>
Sent: Friday, November 25, 2011 6:31 PM
Subject: Re: [Birding-Aus] 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: Re: [Birding-Aus] 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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