[Fwd: Re: The Killers of Oz]

[Colin McHenry <cmchenry@westserv.net.au>]

I forgot to cc this to the list

-------- Original Message --------
Subject:        Re: The Killers of Oz
Date:   Tue, 04 May 2004 13:17:31 +1000
From:   Colin McHenry <cmchenry@westserv.net.au>
To:     marksabercat@yahoo.com
References:     <20040504021319.81281.qmail@web40614.mail.yahoo.com>





Mark Hallett wrote:

> -SNIP
>
> True. We should probably come up with a definition of
> what we mean by "poor soils", which in the tropics
> never have a chance to accumulate to any appreciable
> depth due to microbial/ bacterial action, and yet
> support a much greater plant/animal biodiversity than
> the deeper, supposedly "richer" soils of most
> temperate 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.


Cheers

Colin
*****************
Colin McHenry
School of Environmental and Life Sciences (Geology)
University of Newcastle
Callaghan NSW 2308
Tel: +61 2 4921 5404
Fax: + 61 2 4921 6925

******************
Colin McHenry & Sarah Johnston
14 Summer Place
Merewether Heights  NSW 2291
+61 2 4963 2340
mob: 0423 081683

cmchenry@westserv.net.au
Colin.Mchenry@newcastle.edu.au


--
*****************
Colin McHenry
School of Environmental and Life Sciences (Geology)
University of Newcastle
Callaghan NSW 2308
Tel: +61 2 4921 5404
Fax: + 61 2 4921 6925

******************
Colin McHenry & Sarah Johnston
14 Summer Place
Merewether Heights  NSW 2291
+61 2 4963 2340
mob: 0423 081683

cmchenry@westserv.net.au
Colin.Mchenry@newcastle.edu.au