ALL EXTINCTIONS ARE OUR FAULT
January 25, 2009
eons millions of species have gone extinct naturally, but in modern times
humans are generally the cause of species declines. However, unlike most
other pending extinctions around the world, humans are not to blame for
the imminent extinction of the tuatara of New Zealand.
Tuataras are the sole surviving members of an otherwise extinct taxonomic
group of reptiles. For comparison with other living reptiles, more than
7000 species of snakes and lizards are alive today. A hundred million
years ago, tuataras would not have been considered rare because, as verified
by the fossil record, hundreds of species thrived throughout the world.
Today they are restricted to living on only a few cold, undeveloped islands
off the New Zealand coast.
look like big brown lizards but differ from them by having distinctive
dental, skull, and skeletal features. Their blood cells are larger than
any other living reptile. Tuataras have the remnants of a third eye in
the center of the skull, and although a similar structure has been studied
in some lizards, the function remains unknown. Another tuatara trait also
found in a few lizards is vocalization. Hearing a tuatara croak on a cold,
drizzly night on an uninhabited island a thousand miles from Australia
would presumably bring back some strange emotions related to our own evolutionary
past. They reportedly make a cricket-like sound when picked up.
physiological difference between tuataras and all other living reptiles
is that they require cool temperatures. A well-known characteristic of
other reptiles is that they are only active when they are warm. Most reptiles
do well at temperatures between 70 and 80 degrees F, and some desert lizards
thrive at temperatures above 100. But a tuatara tolerates temperatures
near freezing and is active around 45 degrees but will die at temperatures
much above 80.
reach lengths greater than two feet. They eat mostly small animals, such
as insects, snails, and frogs. They also eat bird eggs and a few small
seabirds that nest on their islands. Tuataras are classified as endangered
and are carefully protected. They are not allowed to be transported out
of the country, even to zoos. Most Americans have never seen a live one,
and most New Zealanders have never seen one in the wild, as the islands
themselves are practically inaccessible.
have a long life span. One was kept in captivity for 77 years, and documentation
that some individuals live more than a century would come as no surprise.
Other age-related phenomena of importance are that these bizarre animals
take up to two decades to reach maturity and more than half a century
to attain full adult size. Female tuataras lay about a dozen eggs, but
at intervals of four years. The eggs take as many as 15 months to hatch.
greatest threats to the remaining tuataras are non-native rats that have
been inadvertently introduced to the islands. A slow-growing reptile with
a low reproductive output that has also evolved without natural predators
can become dependent on extended longevity to assure successful reproduction.
The presence of a new predator that can kill eggs and young could become
a serious threat to the tuatara's continued existence. In fact, the sad
news is that these unusual reptiles are already extinct on some of the
islands invaded by rats. Some conservation biologists contend that humans
are culpable for the introduction of rats and the decline of tuataras.
Sure, we have probably caused the disappearance of some tuataras, but
these last remnants of this bizarre group of reptiles were on the way
out the door to extinction long before humans appeared on the scene. The
majority of the species of tuatara had already disappeared naturally millions
of years ago.
represent a conservation situation different from ones that pit economics
against the environment or politicians against public sentiment. Humans
protect today's tuataras as well as a wild animal can be protected. Other
species of wildlife and other environments have been woefully neglected
or actively mistreated by humans in many ways on a global scale, but when
the last tuatara dies, we really should not blame ourselves.
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