Biology Reference
In-Depth Information
Climate and vegetation histories have proven diffi cult to reconstruct on
the Altiplano of Bolivia. It is topographically one of the most complex re-
gions on Earth, and it is located in the transition between climate regimes
of the far north and the far south. In addition, the Altiplano is infl uenced by
the variable meanderings of the ITCZ; Milankovitch variations, suggested
to have infl uenced the climate in the northern part, have not been detected
in the southern part; tectonic events may have affected drainage patterns
and water tables differently in the separate basins; and there is a lag time
between climatic changes in the marine realm and those on land. Until re-
cently there has been the added complication of carbonate-charged waters
contaminating some sediments used for
14
C dating. It is clear, however, that
between 18.1 and 14.1 kyr, dramatic changes affect the moisture regimes
on the southern Altiplano. Presumably these become evident around 2 Ma,
generally occurring toward the end of each of the approximately eighteen
to twenty glacial maxima. Precipitation increases, and the now-isolated dry
salars expand and fi ll with water (Placzek et al. 2006, 2009). The largest
lakes in the region for the past 120,000 years appear, and some are esti-
mated to have been over 140 m deep. Intervening times are drier, and there
are repeating cycles throughout the Quaternary, giving a dynamic aspect to
life on the Altiplano.
This brings us to Patagonia and Cape Horn, the land of fi re, and the
Beagle Channel—“the uttermost part of the world.” Some modern carni-
vores have already crossed into South America (bears, cats, dogs, otters,
raccoons). These and the saber-toothed cat
Smilodon
may infl ict a price on
the native South American animals, which have little previous experience
with carnivorous mammals, but the majority of extinctions, for example,
of most native ungulates and marsupial carnivores, have happened prior to
the interchange. Newly arriving herbivores include llamas, deer, and tapirs,
which survive; and horses and proboscideans, which do not. In the low-
lands of Chile and Argentina at 2 Ma, Quaternary fl oras and faunas are also
responding to cold/dry and warm/moist cycles. As it becomes colder and
drier, temperate
Nothofagus
(southern beech) forests disassemble into more
isolated patches in protective habitats, while steppe (shrubland/chaparral-
woodland-savanna) expands (Heusser 2003). These repeating cycles in cli-
mate are occurring in the southernmost point of South America, as well
as in the northernmost part of North America, on timescales ranging from
Milankovitch eccentricity variations of 100,000 years, to D-O events of a
few centuries, to ocean-atmospheric induced switches and dials of a decade
or less. The environmental changes of the late Tertiary and Quaternary have
likely served as a pump for generating novel genotypes of relatively recent
