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RE: Pleistocene/Holocene extinctions



> 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.

(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?

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.

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).

NZ, Madagascar, Pacific - Late Prehistoric
extinctions, almost exclusively anthropogenic or due
to human-introduced predators (dogs, Pacific rat etc).
Preceded by Mediterranean islands extinction Late
Pleistocene-Early Holocene, mainly due to the same
causes though hunting figures more prominently.

In conclusion, we don't have a "blitzkrieg" scenario
for the Old World (and it's fairly certain). We do
have one for Australia and the insular regions (fairly
certain also). The case for NAm is equivocal;
extinction pattern in space and time does not
correspond well with known spread of Clovis technology
for example. South America - too many unknowns
regarding tropical regions, but the case that the
Great Interchange served as a kind of "test run" and
thus the number of adaptable taxa was higher than in
NAm cannot be dismissed.


Regards,

Eike

* Long time to maturity, not even close to panmixia.
Deleterious alleles must have been a dime a dozen in
mammoths. Assumption also fits well the disappearance
pattern of Giant Deer. If what's true now was true
then (it most probably was), any isolated
subpopulation smaller than 500-1000 mature individuals
would have stood slim chances of surviving for more
than 100, 200 years. A cheetah's chance basically
(which species was plain lucky to survive whatever
disaster brought it to the brink prehistorically), but
with hunting on top. Today, the Borneo Coluded
Leopard's chances of long-term survival stand probably
better than the Amur Tiger's (because the former is
genetically fairly well adapted to low effective
population sizes and the latter is not at all)


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