Environmental Engineering Reference
In-Depth Information
generally selected the most abundant species and that the continent's late Pleistocene
extinctions were driven primarily by climatic changes; only after the ensuing habitat
fragmentation and reduction of ranges and numbers did human interference, be it
by hunting or by other activities, became important.
As for the demise of Eurasia's largest herbivore, people and mammoths had
coexisted for millennia. There is no evidence of any large-scale hunting of the species
in sparsely populated regions of Siberia, and the gradually unfolding extinctions (no
signs of any blitzkrieg) are best attributed to environmental changes (Reumer 2007;
Stuart and Lister 2007; Kuzmin 2009). The latest support for this conclusion comes
from Allen et al. (2010). They used a global climate model to simulate paleoclimates
during the last glacial stage and early Holocene (42,000-10,000 years before the
present) and concluded that the principal cause of megafaunal extinctions was the
replacement of open and largely treeless glacial stage vegetation, whose mesophilous
herbs had a higher capacity to support large herbivores.
The extinction of mammoths and of other species of the
Mammuthus
-
Coelodonta
faunal complex was driven primarily by sometimes dramatic shifts of dominant
ecosystems, above all the loss of open, grass-dominated landscapes (tundra or steppe
vegetation) and their displacement by tree-dominated formations with mixed
conifer-broadleaf forests in the mid-latitudes, coniferous forests further north, and
peat bogs and tundra in the Arctic. Natural habitat fragmentation created isolated
populations, which then underwent insular evolution that was sometimes marked—
as in the case of the dwarf mammoth of Wrangel Island—by diminished stature
(Guthrie 2004), and human predation could have hastened the demise of some of
these isolated and vulnerable species, surviving in fragmented refugia.
Even so, some animals previously thought to have become extinct by the late
Pleistocene made it far beyond the Pleistocene-Holocene transition. Stuart et al.
(2004) showed that the giant deer (Irish elk) survived in western Siberia more than
three millennia after its previously accepted extinction date, to around 7,700 years
ago. There were at least two Holocene mammoth refugia, in Siberia (Kuzmin 2009)
and on Wrangel Island in the high Arctic, where small-sized mammoths survived
well into the Holocene, with the youngest radiocarbon-dated tusk as recent as 2,038
BCE (Vartanyan et al. 1995), contemporary with ancient Egypt's Tenth Dynasty. A
new dating of an American mastodon from northern Indiana shows that the species
survived beyond the Clovis period into the late Younger Dryas time (Woodman and
Athi eld 2009).
And new radiocarbon dates from Alaska and the Yukon Territory (AK-YT) show
that steppe bison (
Bison priscus
) and wapiti (
Cervus canadensis
), the two species of
