| There are two main types of tortoises on the the Galapagos Islands:
one has a domed shell, short neck and lives on the moister islands; the
other variety has a shell that flares up in front so that its long neck
can be raised high. The long-necked variety lives on the more arid islands
where there are mainly shrubs and prickly pear bushes. Today the giant
tortoises are mostly very rare and protected by law.
Can you think of a reason for
the difference between the two main types of tortoises?
Each island has its own sub-species of tortoise, having a particular
shape, colour, shee thickness, neck length and size. The local people could
tell which island a tortoise came from, by the shape of its shell.
The tortoises' main food is prickly pear (cacti). Darwin noticed
that on islands where there are no tortoises the prickly pear was low and
spreading with soft spines. On islands where there were tortoises, the
prickly pear grew more upright and had stiff spines.
Can you suggest a reason for
the different shapes of the prickly pear? |
