Re: Subterranean strategies

["Adam Britton" <abritton@wmi.com.au>]

From: "Ken Kinman" <kinman@hotmail.com>
Sent: Thursday, July 19, 2001 12:05 AM


>      But we weren't really discussing what caused the extinctions per se

Maybe that's why nobody can come up with a satisfactory explanation.


> (the impact scenario is now pretty widely accepted as a given).

The fact that an impact occurred is fairly widely accepted, but that tells
us little about the actual causes of extinction. Even if we postulate that a
gigantic ash cloud enveloped the sun, or toxic fallout rained down on some
area of the landscape, it doesn't address the impact these had upon
different species. We can only assume that the impact triggered a series of
scenarios that led to extinction in different environments, rather than a
single, simple explanation that caused so many different groups to
disappear. What about the resilience or susceptibility of species to
different components of an extinction scenario?

On a general theme, if one looks at modern species, we see that many are
highly resilient to "population pressure" - they can recover from drought,
lack of food, human hunting pressure, climatic change etc. Many even change
their reproductive strategies to cope (eg. kangaroos) or have an "in-built"
mechanism that becomes far more effective at recovery after a decline,
particularly in long-lived species (eg. crocodiles). However, other species
cope less well with these population pressures, such as those with low
fecudity rates. The survivors of extinction events are those most able to
deal with population pressure, or those isolated from its effects (isolation
includes species upon which they rely, eg. for food). The question is, what
were the different effects, and what makes certain species more resilient to
them than others?

Adam