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Tapirs evolved in North America at
least 50 million years ago. They spread
to and now live in Central and South
America, as well as southeast Asia, but
died out in North America.See also: Modern view of diversity 90–91 ■ Animal ecology 106–113 ■ Island
biogeog raphy 14 4 –149 ■ Big ecology 153 ■ Climate and vegetation 168–169ORGANISMS IN A CHANGING ENVIRONMENT
data. This holistic approach is best
illustrated in his highly detailed map
and cross section of Chimborazo
mountain in Ecuador.Wallace’s contribution
Many 19th-century naturalists
contributed to biogeographical
knowledge, but one of the most
significant was British naturalist
Alfred Russel Wallace. After reading
Philip Sclater’s account of the global
distribution of bird species, Wallace
set out to do the same for other
animals. He examined all the factors
known at the time to be relevant,
including changes in land bridges
and the effects of glaciations. He
produced maps to demonstrate
how vegetation influenced animal
ranges, and he summarized the
distribution of all known families
of vertebrates.
Wallace then proposed six
zoogeographic regions, which are
still largely in use today: the Nearctic
(North America), Neotropics (South
America), Palearctic (Europe, north
Africa, and most of Asia), Afrotropics
(south of the Sahara), Indomalaya
(South and Southeast Asia), and
Australasia (Australia, New Guinea,and New Zealand). The dividing line
between these last two regions,
which runs through Indonesia, is
still known as “Wallace’s Line.”Plate tectonics
Wallace also made some remarkable
discoveries from the fossil record.
For example, he worked out that
early rodents had evolved in the
Northern Hemisphere, moving via
Eurasia into South America. Later,
in 1915, German geologist Alfred
Wegener proposed the radical idea
that the continents of South
America and Africa were once
connected, which allowed the
spread of tapirs and other species.
Wegener understood that the
distribution of species was in part a
record of geological history. Species
colonize new areas as conditions
change, and over time have become
separated by barriers such as
new oceans or mountain ranges.
Today, as human-made changes to
climate and the environment gather
pace—creating new barriers—this
understanding has taken on a new
and vital importance. ■Alexander von
HumboldtKnown as the “founder of plant
geography,” Humboldt also
made valuable contributions
to geology, meteorology, and
zoology. Born in Berlin in 1769,
he started collecting plants,
shells, and insects at an early
age. His expedition to Latin
America in 1799–1804
encompassed Mexico, Cuba,
Venezuela, Colombia, and
Ecuador, and his team broke
the world altitude record when
they climbed to 19,285ft
(5,878m) on Chimborazo.
Humboldt also speculated
that volcanoes result from
deep subterranean fissures,
investigated the decrease in
temperature with altitude, and
discovered that the strength
of Earth’s magnetic field
decreases away from the
poles. The 23-volume work
detailing his expedition set a
new standard for scientific
writing, cementing his fame.Key works1807 Essay on the Geography
of Plants
1805–1829 Personal Narrative
of Travels to the Equinoctial
Regions of the New Continent
During Years 1799–1804The unity of nature
means the interrelationship
of all physical sciences.
Alexander von
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