[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Fwd: RE: Pleistocene/Holocene extinctions




Date: Thu, 20 Sep 2007 20:11:52 +0200
To: koreke77@yahoo.de
From: Tommy Tyrberg <tommy.tyrberg@norrkoping.mail.telia.com>
Subject: RE: Pleistocene/Holocene extinctions

At 17:32 2007-09-20, you wrote:

> Hmm...are African animals harder for humans to hunt
> and more dangerous towards them than species from
> other regions? This could be rich territory for
> animal behavior research to explore.

It is ultimately more a question of the right habitat,
probably.

Here's what I have picked up:

Eurasia - Pleistocene/Holocene extinction; main
causes: climate change (habitat shifts therefrom) and
hunting as a kind of pincer. Latest results from Giant
Deer indicate that population became caught between
shrinking habitat and an expanding human population.
Minimum viable populations for especially Siberian
megafauna must have been HUGE (among the largest of
all organisms*) due to topography and (ice age)
habitat distribution being essentially barrierless
between Urals and Bering Strait. Hence, populations
highly vulnerable to fragmentation. Exactly what
happens to the Amur Tiger as I write by the way. But
overall, few extinctions. Secoind wave in Early Modern
era in Europe - arguably still continuing -, due to
habitat destruction and (to a lesser degree)
overhunting.

Extinction here was stepwise. Southern European forms (Forest Elephant, Forest Rhinoceros, Hippopotamus, Neanderthalers) went in the mid-Weichselian soon after H. sapiens arrived. In northern Europe the main extinction happende in the latest Pleistocene and into Early/Mid Holocene in northern Siberia.
I don't think the "mammoth steppe" megafauna necessarily required large minimum populations. They had all survived previous interglacials (and during the Eemian there was very little tundra left in Siberia). Also the Mammoth survived for 6,000 years on Wrangel's land and 4,000 years on St Pauls island. Those populations can't have been very large,




(North) America - some confounding factor -
megadisease? anthropogenic habitat alterations? There
is a pattern of ecosystem collapse that is too diffuse
in timing and duration to pin on either humans or
climate with a good degree of certainty. Scale of
extinctions more massive than in Eurasia. Most
mysterious case; no geographical (except some
climatological) barriers exist between Rockies and
Appalachians. Perhaps high MVP also?

That's not how I read the record. I think everything points to a quite abrupt extinction 10,000-11,000 rcy BP. Admittedly I'm more familiar with the avian than the mammalian record. The avian extinctions incidentally seems to have been mostly driven by the mammalian extinctions.



Australia - probably mainly human-altered fire regime
(and other ecological changes) since Latest
Pleistocene, some hunting, end of ice age was only
coup de grace. The case is rather clear here: there is
a good pattern of extinction and ecosystem shift that
too closely concides with human range expansion to be
dismissed easily. End of ice age for example seems to
have been a factor in thylacine disappearing from
mainland, but most extinctions down under were already
done by then.

No - the Thylacine survived until about 4,000 BP, it probably was outcompeted by the dingo which came in at about that time. There may have been a second thylacine species in New Guinea that did become extinct in the early Holocene, but that is uncertain.


Africa - little extinction, mainly because everything
that humans could do to an ecosystem with stone age
technology had been tried in the millennia before.
Adapation strategies may have been behavioral, but
mostly it is likely to have been a kind of general
ecological adaptation - avoiding those funny erect
apes whenever possible, and/or proliferating to a
"safety in numbers" strategy.

South America - rather less human-caused extinction
apparently, but the case here seems most similar to
(Eur)Asia. Though it is not known (and much will never
be known) what lived in the Amazon Basin before that
became covered with rainforest, and what happened to
these critters (humid-mesic open woodland and
grassland was probably the ice age vegetation in
Amazonia).

I would say that South America was hit worst of all continents. There are almost *no* large animals left in non-forested habitats (North America at least has Buffalo and Pronghorn) South America has practically nothing except Guanaco in Patagonia. In the campos and llanos of northern South America there is absolutely nothing (unless you count Giant Anteater or Capybara)


Timing here is not very well constrained, but there is some evidence that at least some megafauna survived into the early Holocene in Patagonia.

Tommy Tyrberg