Christmas Bells

Christmas Bells
Christmas Bells - Blandfordia nobilis

Wednesday, May 23, 2012

A follow-up re "disjunct populations" and climate change

You may recall my post last week about the Olearia ramosissima - a small Daisy with a "disjunct population' - split by the desertification of the Nullabor Plain (presumably as a result of naturally-occurring climate change).

I subsequently wrote an article for the local REPS (Robertson Environment Protection Society). 

  • This species has a “disjunct distribution” - split between Western Australia (Esperance region) and northern NSW, but with a couple of outlying records, including one, crucially from Shoalhaven Gorge. That links the known range of his plant directly with where I found it, about 30 Kms further down river from the Shoalhaven Gorge. 
  • Distribution Map from Atlas of Living Australia
    Olearia ramosissima
  • The distribution map for this species reminds me of several other Australian organisms which have disjunct distributions.  When I was growing up in Melbourne (a long-time ago) I was introduced to the wonderful world of Australian birds courtesy of Neville W Cayley’s “What Bird is That?”. In birding circles, the classic cases of disjunct populations like this are the Eastern and Western Spinebill, and the Eastern and Western Bristlebird. But there are other examples, such as the various species of white-tailed Black-Cockatoos in Western Australia. It is accepted that these birds have speciated away from their cousins in the east of Australia (or possibly it is the other way around) because the eastern and western populations of those birds are considered to have been separated by habitat changes. This was always explained to me in terms of the pre-historical drying of the Australian continent, resulting in similar members of a family of animals becoming separated because of the intrusion of the arid zone of Central Australia into the middle of their presumed original continuous range across southern Australian.  
  • My image of Eastern Spinebill on Grevillea
  •  
    Keith Lightbody's photo of Western Spinebill (Wikipedia)
  • So, I cannot help speculating that the distribution of this plant is an example of long-standing Climate Change. Before my comments are misinterpreted as an argument against the current “climate change” argument, I mean no such thing. 
  • Clearly speciation of plants and animals with disjunct ranges such as this has occurred over a lengthy period of time. But that is no reason why mankind ought to alter the global climate by deliberate pollution of the atmosphere with carbon dioxide and other chemicals.
On the issue of climatic changes and speciation I have found this article in the Canberra Times.
It includes these comments:
  •  Edwards explains that when isolated populations of birds form in a landscape, one of the first traits to change is song - ''just like geographical differences in human language''. Over the past decade, he's been studying genetic divergence in bird populations across the Gulf country's savanna in north-west Queensland. There's a region known as the Carpentarian Barrier - ''a line running south from the Gulf through Normantown (sic***)'' - which appears to mark an evolutionary population divergence for a number of species, including grass finches, wrens and treecreepers.
    ''It's intriguing, because if you drive across it, there aren't immediately visible differences,'' he says. ''It's more open, there are fewer trees and the vegetation on either side looks quite similar. It's very subtle, nothing that would shout out at you, 'Things cannot pass through this barrier!' ''
    ''There are some possible culprits, such as desertification, that may have caused genetic paths to diverge. It's possible sea levels may have risen and fallen and that may have served to isolate populations.''
    Using DNA samples, Edwards and research colleagues can measure genetic differences on both sides of the barrier. They can also establish if populations diverged at around the same time, or if successive waves of genetic divergence occurred. The value of this research lies in mapping the genetic geography of Australia's biodiversity, he says.
    ''It's the geography of genetic diversity. There's a lot of interest in maintaining biodiversity, particularly given the impacts of climate change, and one of the goals of conservation is to preserve areas of habitat that have a high level of genetic diversity…
    ''There's also a growing interest in - and it's a heady concept - of preserving evolutionary processes, and setting aside areas where evolution is proceeding rapidly. So that's where phylo-geography can be beneficial, in mapping areas of genetic divergence.''
    The perspective on conservation is changing, he says. Last century, writers like Aldo Leopold were ''ruminating on the importance of species'' and the need to preserve ecosystems as nature reserves.
    ''Now, the question has shifted to how do we keep these ecosystems functioning? How do we mange them against the onslaught of invasive species and climate change, and maintain their diversity, fertility and ecosystem function?
    ''We've lost the preservationist battle. It's no longer a viable option to try to restore these places to what they once were, because every habitat has experienced some sort of insult. We have already gone too far.''
  • *** My Northern Australian correspondent, Brigid, wishes to correct the spelling of "Normanton". She has also raised other interesting geographical questions which I cannot answer. I shall refer the questions to Canberra ornithologists who  might be in contact with

There is much to think about in Roslyn Beeby's article (linked above).


1 comment:

Brigid O'Carroll Walsh said...

Very interested in the description of the Carpentaria Barrier. All my years of living in North Queensland the Northern Territory, I had never heard of it. BTW, don't know whether it was Mr Edwards or a typo, but the name of the town is Normanton. I have never heard of it, even historically, being called Normantown.

Is there any mention of how far south from Normanton the Barrier goes. You see, south of the Gulf is the Barkly Tableland. The Barkly Tableland extends from just east of Cloncurry in Queensland across to (more or less) the Stuart Highway in the Northern Territory. I don't know where its northern limits lie below the Gulf but in the NT, the Carpentaria Highway would be a rough northern demarcation. It's southern limits, I think, would not be too far south of Cloncurry and Mount Isa in Queensland. In the NT, it stops around Barrow Creek about 2 hrs south of Tennant Creek. This is all savannah country and Mitchell grasses. Good cattle fattening country. I would be interested to know if the Carpentaria Barrier slices through The Barkly.