Biology Reference
In-Depth Information
The flora and fauna on islands recently connected to the mainland—as with Sri Lanka to
India or Trinidad to South America—are similar to those on the nearby mainland, so newly
arriving species must cope with predators and herbivores they encountered on the mainland.
But species that established themselves on islands that were never connected to the mainland
or were otherwise far from continental coasts typically evolved in the absence of predators.
The “naive” resident fauna lacked appropriate escape behavior, even birds that could simply
have picked up and flown away at the first hint of danger when predators, including
Homo
sapiens
, were introduced. As a result, most vertebrate extinctions during the past several cen-
turies have occurred on islands. Such ecological naïveté extends to plants, too. As we shall
see in the case of Hawaii, plants that evolved over time in the absence of large herbivores lost
their chemical defenses and physical structures such as thorns and prickles; they suffer ter-
ribly when exposed to introduced goats, deer, sheep, and rabbits. An often overlooked group
of exotic, invasive organisms are invisible to the naked eye—bacteria, viruses, and protozo-
ans that cause outbreaks of disease. In some areas, introduction of disease-causing organisms
has been even more deadly for rare natives that have had no previous cause to develop anti-
bodies than have been creatures with backbones. Hawaii has been hard hit on the microscopic
front as well.
So much attention has been given to recent invasions as part of the contemporary biod-
iversity crisis that we lose sight of the fact that some ecologically catastrophic invasions
happened long ago. The first biodiversity crisis in Hawaiian history occurred when the
Polynesians arrived more than 1,000 years ago, bringing with them slash-and-burn agricul-
ture, pigs, and stowaway rats that scurried to shore. Combined with the unwelcome ark of
more recent invaders that Europeans introduced—sheep, goats, cattle, deer, mongooses, and
mosquitoes—these foreigners now plague an archipelago with perhaps the highest concentra-
tion of rarities on Earth. Ironically, while the suppression of malaria played a significant role
in the decline of the rhinoceros in Nepal, the introduction of malaria in Hawaii has decimated
a group of native birds, the honeycreepers.
That some of the spectacular native species are still holding on, such as the woodpecker-
like
'akiapōlā'au
, demands our attention. Many evolutionary biologists, such as Stanford
University's Peter Vitousek, a native son, view the string of South Pacific islands collectively
called Hawaii as America's Galápagos Islands. If Hawaii's multitude of endemic species has
often been decimated by invasives, this cradle of evolutionary exuberance, like Darwin's liv-
ing laboratory, is also a showcase for how natural selection and isolation have combined to
foster new species, many of them rare. Hawaii supports the highest percentage of plants and
animals found nowhere else. For example, of the nearly 1,000 species of flowering plants
found in Hawaii, 90 percent are restricted to the islands. This unusual level of endemism
and such narrow ranges means that if we lose a piece of wild Hawaii, we lose many species
forever.
