Giant Tortoise
 No animal is more synonymous with the Galapagos Islands than
the giant tortoise. Indeed, the saddle-back shape of the shell
in many of the tortoise races reminded the early Spaniards of
a type of riding saddle called "galapago", and this
term is also applied to the tortoises. Hence, by calling the islands
the Galapagos, we are, in essence, calling them "The Islands
of the Giant Tortoises"!, The giant tortoise is the symbol
of both the Charles Darwin Research Station and the Galapagos
National Park Service. In the form of one particular individual,
Lonesome George, the sole surviving member of the Pinta Island
race, the giant tortoise is the symbol of extreme fragility of
the Galapagos islands, and a reminder of the need for vigilence
and conservation.
It was also the giant tortoise that tipped Darwin
off to the incredible diversity of the Galapagos fauna and flora.
In the "Voyage of the Beagle," he noted:
I have not as yet noticed by far the most remarkable
feature in the natural history of this archipelago; it is, that
the different islands to a considerable extent are inhabited
by a different set of beings. My attention was first called
to this fact by the Vice-Governor, Mr. Lawson, declaring that
the tortoises differed from the different islands, and that
he could with certainty tell from which island any one was brought.
I did not for some time pay sufficient attention to this statement,
and I had already mingled together the collections from two
of the islands. I never dreamed that islands, about fifty or
sixty miles apart, and most of them in sight of each other,
formed of precisely the same rocks, placed under a quite similar
climate, rising to a nearly equal height, would have been differently
tenanted; but we shall soon see that this is the case. It is
the fate of most voyagers, no sooner to discover what is most
interesting in any locality, than they are hurried from it;
but I ought, perhaps, to be thankful that I obtained sufficient
materials to establish this most remarkable fact in the distribution
of organic beings.
There are 15 recognized races of tortoise, all
generally considered to be members of the single species Geochelone
elephantopus.. The genus Geochelone itself is represented
by a cluster of species of small to medium-sized tortoises in
South America, Africa, Madagascar, and Asia. In the past, giant
species of Geochelone were once found on all continents
except Australasia, but today the giant forms are restricted to
G. elephantopus in the Galapagos and G. gigantea
on the island of Aldabara. There are a number of captive G.
elephantopus populations in zoos around the world and it seems
that fertility is lower in those zoos that permit breeding between
members of different races. The reasons for this reduced fertility
are unclear, but it is not possible at this point to rule out
genetic factors. The basic definition of the term "species"
includes reproductive incompatibility with other species. If this
reduced fertility does indeed turn out to be genetic, then the
the degree of relatedness between the 15 Galapagos races and their
taxonomic status become unclear.
Of the 15 races of Galapagos tortoises, four are
extinct. Because of breeding and release efforts on the part of
the Charles Darwin Research Station, most of the remaining races
are holding their own. However, there is still on-going poaching
of tortoises by local residents. One race, that from Pinta is
represented by a single surviving male, aptly named Lonesome George.
The 15 races are:
|
Genus
|
species
|
race
|
Island
|
|
Geochelone
|
elephantopus
|
elephantopus |
Floreana (extinct) |
|
"
|
"
|
not described |
Santa Fe (extinct) |
|
"
|
"
|
phantastica |
Fernandina (extinct) |
|
"
|
"
|
wallacei |
Rabida (extinct) |
|
"
|
"
|
hoodensis |
Espanola |
|
"
|
"
|
abingdoni |
Pinta |
|
"
|
"
|
ephippium |
Pinzon |
|
"
|
"
|
chatamensis |
San Cristobal |
|
"
|
"
|
darwini |
Santiago |
|
"
|
"
|
vicina |
Volcan
Cerro Azul Isabela |
|
"
|
"
|
guntheri |
Volcan
Sierra Negra, Isabela |
|
"
|
"
|
vandenburghi |
Volcan Alcedo,
Isabela |
|
"
|
"
|
microphyes |
Volcan Darwin,
Isabela |
|
"
|
"
|
becki |
Volcan Wolf, Isabela |
|
"
|
"
|
porteri |
Santa Cruz |
The circumstances surrounding three of the four
extinct races are unclear:
G. e. phantastica,
the Fernandina form, is known from only one specimen, a male,
found by members of the 1906 San Francisco Academy of Sciences
expedition. Nothing more turned up until 1964 (!) with the discovery
of putative tortoise droppings. However, no other tortoise,
living or dead, has been found on Fernandina
and it is entirely possible that that one lone male was a stray
or a release. Fernandina is the most
pristine of the islands and any tortoise population would not
be likely to have become extinct at the hands of introduced
animals. If G. e. phantastica is, indeed, a real race,
then it is the only one to become extinct by natural means.
Similarly, G. e. wallacei, from Rabida
is known from only one specimen. Tracks were seen on Rabida
in 1897 and a single individual was removed by the Academy of
Sciences in 1906. No logs from whaling or sealing vessels which
are known to have collected tortoises for food make any mention
of collecting at Rabida. On the other hand, Rabida has
a good anchorage and nearby is the remains of a corall in which
tortoises, perhaps from other islands were temporarily held.
The type specimen of G. e. wallacei, the individual from
which the race was named, actually has an unknown provenance:
it was assigned to Rabida because it
resembled the one removed in 1906. Thus G. e.wallacei
could be an escapee from another island.
The situation on Santa Fe
is equally unclear. Like Rabida, Santa
Fe has a good harbor and the terrain is fairly gentle. But
there are only 2 records of whalers removing tortoises, and
there are two eye-witness accounts of locals removing tortoises
in 1876 and 1890. These accounts, however, were given 15 and
30 years after the fact. The academy expedition found old bones
(but no shell fragments, the most durable part of a tortoise
skeleton). Given the confusion over island names, it could well
be that the reports are mistaken, and the bones the remains
of butchered tortoises taken ashore by visitors. There has never
been enough material to describe a race.
Thus although Fernandina,
Rabida, and Santa Fe are listed as having
extinct races, the races are questionable.
The extinct race on Floreana,
on the other hand, is far from questionable. Darwin saw them in
1835, and noted that tortoises comprised the main food item in
the Floreana colony; "two days hunting
will  find food for
the other five in the week." Although he commented on how
the numbers had been obviously reduced from those in years past
("not many years since the Ship's company of a Frigate brought
down to the Beach in one day more then 200"), he did mention
Vice Governor Lawson's prediction that "there is yet sufficient
for 20 years." Indeed there is a well-documented record of
heavy collecting in the years leading up to Darwin's visit, but
then just three years later, a visiting ship could find no tortoises
and in 1846, another visitor declared them extinct. Descriptions
of the Floreana race, G. e. elephantopus
are based on skeletal material from individuals who fell down
into lava tubes and died. On my first visit to Galapagos in 1989
I saw such bones in the cave near the Post Office Barrel.
|
