Re: K-T Theories

[Derek Tearne <derek@nezsdc.fujitsu.co.nz>]

On the introduction of Myxamatosis to the Australian rabbit 
population.  First it should be pointed out that rabbits themselves
are an introduced species with no natural predators in Australia.  This 
means that, unchecked, they can simply breed until there is no food left 
for them to eat (a slight simplification).  So the situation is slightly
artificial in that the disease is the _only_ pressure on the species in 
question.
  
> Mickey tells me in email that there was just one disease
> released into the population, which pretty well blows
> _that_ idea.  It still intrigues me, though.  Perhaps
> in my copious free time I'll take up his offer of a
> reference for disease propogation and take a stab at an
> alife simulation, just for kicks.  

The major problem with using disease to eradicate the rabbit population
is that it is very rare indeed for a disease to affect every single 
member of a population.  Some members will almost inevitably make it 
through.  The progeny of these survivors will be quite likely to also
have a good chance of surviving when the disease strikes again.

Bakkers model is one of brand new and virulent diseases being passed 
across a land bridge to new populations which have no immunity.

The Black Death in Europe only killed something like a third of 
the population (I'm running from memory here, it was certainly less 
than 50%).  Even where this has happened to human populations in recent 
times and several diseases at once have been introduced (measles, 
smallpox et al into Hawaii, Australia, New Zealand) the populations have 
managed to survive.

The population decline of the native Hawaiians after Cook laid over there
and during the first few years of colonisation are quite horrific.  Recent
evidence in Australia (from burial sites in Lake Victoria, a large artifical
lake on the Murray river) shows that the pre-european population was
significantly larger than originally estimated.  The diseases introduced
by the first explorers travelled inland much faster than the explorers/
colonists could, so when they arrived in the interior they found a 
sparcely populated land and assumed it always had been so.

So even in these extreme cases extinction did not occur (the populations 
had survived and would have recovered on their own).  Admittedly the 
human population of Australia had few natural predators and, like the 
rabbit, is a succesful introduced species.

Of course Vicki's point about the rapid breeding cycle of rabbits is 
a valid one.  However there must surely have been _some_ small dinosaurs 
which were capable of rapid breeding.  Certainly I doubt that there are 
many animals extant or otherwise which require as extensive parenting 
as humans.  

If we can survive exactly the disease introduction scenario Bakker
proposes then surely some of the dinosaurs could have done so.       

> - of course,
> the idea of a gov't introducing new diseases is a creepy
> one, so perhaps we'd best let it lie.

Especially as the introduction of the disease didn't work.  Although
biological  control agents are very appealing they are much more 
tricky to get right than chemical methods.  After all the Cane 
Toad is another Australian environmental control 'success' story.
The introduction of the African Dung beetle to Australia however is a 
genuine success story (impressive reduction in the fly populations).

Sorry if this has digressed from dinosaurs a little.  I think it can
be very illuminating to look at modern examples of disease and new 
species introduction, especially as there are so many available.

--- Derek


Derek Tearne.   --   derek@fujitsu.co.nz   --    Fujitsu New Zealand   --
Some of the more environmentally aware dinosaurs were worried about the
consequences of an accident with the new Iridium enriched fusion reactor.
"If it goes off only the cockroaches and mammals will survive..." they said.