Re: The Killers of Oz

[Mark Hallett <marksabercat@yahoo.com>]

Dear Colin, Thanks, those were all excellent points
that I hadn't considered. Vis-a-vis dinosaur
paleoecology, the differences you described for the
various regions of Australia have a lot of potential
relevance when it comes to interpreting formations
like the Morrison, which in the past have inspired
widely different interpretations of the depositional
environments. The Morrison was a huge area, and there
could have been considerable variation in plant
productivity within the entire region. --Mark   
--- Colin McHenry <cmchenry@westserv.net.au> wrote:

---------------------------------
    

Mark Hallett wrote:
  
-SNIP
  
True. We should probably come up with a definition
ofwhat we mean by "poor soils", which in the
tropicsnever have a chance to accumulate to any
appreciabledepth due to microbial/ bacterial action,
and yetsupport a much greater plant/animal
biodiversity thanthe deeper, supposedly "richer" soils
of mosttemperate regions.--Mark Hallett    

Mark, rainforests don't always have poor soils - just
consider the beautiful forests around the Atherton
tableland, sitting on all those volcanic soils (and
anyway, what do you mean "former Australian" - you
don't get away that easy...).  Unlike the famous and
oft-quoted cases in Brazil, areas of that forest that
have been cleared for farming have been productive for
a long time now.Perhaps there might be a difference
between the average soil quality of lowland, basin
rainforests (e.g. Amazon), compared with the montane
and semi-montane forests (e.g. Eastern Australia). 
But I doubt it would even be that simple.  Soil
quality will certainly affect which plnats can grow
there - but the basic rainforest physiognamy can be
made up of lots of different species combinations,
just as woodland can be.  There are pockets of
rainforest in the Blue Mountains (sandstone derived
soils - very poor) which are very different to the
rainforest that sits on the basalts in Queensland. 
Soil type is just one of a number of factors
(rainfall, fire regime, grazing regime) that
determines physiognomy.As far as the original point of
this thread is concerned, anyone looking for a simple
link between productivty and diversity is going to be
disappointed.  This is true in marine environments as
well as terrestrial.  Productivity and total biomass
are more likely to be linked, but it is how that total
bimass is chopped up (i.e. species diversity, biomass
of constituent species/individuals) that most people
have been arguing about, and there are no clear rules
about how this happens...which means we need to pay
more attention to the specifics of
palaeo-synecological reconstructions, because the
generalisations are not so useful.In the Australian
example, Flannery's 'poor soil' hypothesis sought to
exlain the apparent lack of large mammals in the
Australian Upper Cenozoic by invoking a factor (low
overall productivity) that does not have clear
relationships with patterns of species diversity or
the range of body sizes at a given trophic level.  I
think the basic point that Steve Wroe is making is
that basic island-biogeographic theory explains the
patterns of diversity and body size in Australian
mammals much better than does the 'poor soil'
hypothesis.  Also interesting is Wroe's point that
Australian Upper Cenozic mammals weren't that small
after all - the biggest diprotodonts get up to 2 - 3
tonnes, and Thylacoleo is over 100kg (i.e. bigger than
a jaguar - equivalent to a small lion).And don't
forget the extensive rainforests of the Miocene - the
Great Artesian Basin was covered in a rainforest at
least as big as the recent    Amazon back then. 
Remember, average body size is smaller in forest
animals relative to their open grass/woodland
relatives, and the largest  elephants today live in
the Namib desert.  And neither of these observations
is at all surprising, if you think about
it.CheersColin*****************Colin McHenrySchool of
Environmental and Life Sciences (Geology)University of
NewcastleCallaghan NSW 2308Tel: +61 2 4921 5404Fax: +
61 2 4921 6925******************Colin McHenry & Sarah
Johnston14 Summer PlaceMerewether Heights  NSW 2291+61
2 4963 2340mob: 0423
081683cmchenry@westserv.net.auColin.Mchenry@newcastle.edu.au




        
                
__________________________________
Do you Yahoo!?
Win a $20,000 Career Makeover at Yahoo! HotJobs  
http://hotjobs.sweepstakes.yahoo.com/careermakeover