Endangered tortoises face
new threat on Galapagos Islands
When Charles Darwin
arrived in the Galapagos Islands 165 years ago, he was
astounded by the sight of thousands of giant tortoises,
some with shells 7 feet in circumference. Darwin wrote:
As I was walking along
I met two large tortoises, each of which must have
weighed at least two hundred pounds: One was eating a
piece of cactus, and as I approached, it stared at me and
slowly walked away; the other gave a deep hiss, and drew
in its head. . . . I frequently got on their backs but I
found it very difficult to keep my balance.
At first, Darwin, like
most human visitors, considered tortoises little more
than food. But he was intrigued when the Spanish
vice-governor of the Galapagos claimed he could identify
which tortoise came from which island by the unique shape
of its shell.
When Darwin returned to
England, he realized that the vice-governor was correct:
Nearly every major island in the Galapagos archipelago
had its own variety of tortoise that had evolved over
time. Thus, the giant tortoise became a cornerstone of
Darwin's theory of evolution through natural selection.
Since Darwin's visit, the
Galapagos giant tortoise (Geochelone elephantpus)
has had a difficult time surviving in the wild. Hundreds
of thousands of tortoises were slaughtered for food in
the 1800s. Today the population is around 15,000, down
from an estimated 250,000 in Darwin's day.
Three of the 14 subspecies
of giant tortoise that originally inhabited the islands
are extinct. Remarkably, Isabela Island alone boasts five
distinct subspecies living on five separate volcanoes:
Wolf, Darwin, Alcedo, Sierra Negra and Cerro Azul.
Volcanic eruptions have
been part of the natural order in the Galapagos for
millions of years, but biologists decided to evacuate
tortoises during the 1995 Cerro Azul eruption because the
volcano's unique tortoise population had become
dangerously low.
In addition to its
enormous size, the Galapagos giant tortoise also enjoys
extraordinary longevity. One captive specimen is believed
to be more than 165 years old, which means that it was
alive when Charles Darwin journeyed to the Galapagos as a
young man.
-- Mark Shwartz SR
|
