From: John Bois <jbois@umd5.umd.edu>
Reply-To: jbois@umd5.umd.edu
To: dinosaur@usc.edu
Subject: RE: Armadillos at the K/T!
Date: Sat, 29 Sep 2001 18:13:43 -0400 (EDT)
>...in all natural ecologies, the prescence of an egg-eater or
> predator upon eggs or newly hatched young, or what have you, are part of
an
> equilibrium,
> fluctuating between the extremes of too many prey, to many predators.
There
> is no upset in this
> equilibrium without the introduction of an alien prescence.
I don't think this statement can be made without examination. First of
all
it assumes a steady state system--ecologies are certainly not this over
any
meaningful expanse of time (otherwise evolution would not be seen).
Secondly, whether a predator is home grown or alien, it all looks the
same
to the prey. Yes, aliens may catch residents unawares in an evolutionary
sense. But this is not suggest--and certainly no law exists--that
sympatric
species cannot evolve traits for which their fellow countryspecies must
have
an evolutionary response. Thirdly, while it makes good sense,
predator/prey
oscillations around theoretical carrying capacity is illusive to test,
and I
know of no study which shows this to be the case.
>We have used the bolide hypothesis to
>suggest that catalyst to many disrupted ecologies from the Devonian on.
> There is evidence for
>this.
Evidence of impacts, yes. None for direct causation, however.
>Egg-eating species are naturally in balance with their prey, such as
coatis
(there are animals
>like jagarundis and cougars, even peccaries, that will, can, and have
> [killed] coatis for their
>predatory ravaging of the young. Never in a natural ecoogy to egg- or
> young-feeders decimate a
> population of prey.
Millions of species have become extinct over geological time. We have a
fair idea of the causes of only a handful. How can one claim extinction
is
_never_ due to predation on young. This is especially difficult to argue
when we realize that by far the most severe cause of mortality in many if
not most species is _predation on the young_. Also, "natural ecologies"
are
the denumen of all previous struggles for survival. Species that
couldn't
cope are gone! This is to say that the effectiveness of strategies
changes
over time in response to those that may exploit those strategies.
>The
> mammals present which may have predated upon eggs or young (in the
> Creataceous) are not of a size, sans *Mesodma* and
> one or two other forms (as big as a badger, still smaller than most
> effective extant nest-robber
Badger-size is a threshold under (or around) which many offspring
predators of today operate: hairy armadillo, caracara hawk, coatis,
monitor lizards, skunks, squirrels, cats, rats, weasels, foxes...I could
go on.