Dwarf elephants? Giant rats? Strange island creatures at high risk
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[March 10, 2023]
By Will Dunham
WASHINGTON (Reuters) - A dwarf elephant the size of a Shetland pony once
roamed the Mediterranean island of Cyprus. In the West Indies, a giant
rat-like rodent tipped the scales at more than 400 pounds (180 kg),
rivaling an American black bear.
They were examples of the "island effect," a rule in evolutionary
biology describing how large-bodied species tend to downsize on islands
while small-bodied species upsize. These island dwarfs and giants - a
menagerie also including pint-sized hippos, buffaloes and wolves - long
have faced an elevated extinction risk that, according to a new study,
is intensifying, imperiling some of Earth's most unique creatures.
Focusing on island-dwelling mammals, researchers said on Thursday they
examined 1,231 existing species and 350 extinct ones spanning the past
23 million years. Extinction risk was seen highest among species that
underwent more extreme body size shifts compared to mainland relatives.
And the arrival of people on the islands raised extinction rates more
than tenfold.
"Unfortunately, the slope of the extinction curve that began with the
arrival of the first human voyagers and continued with the later waves
of colonization has become even steeper in recent decades," said
paleoecologist Roberto Rozzi of the Natural History Museum of Martin
Luther University Halle-Wittenberg in Germany, lead author of the study
published in the journal Science.
Islands foster unique evolutionary dynamics. For large-bodied species,
there is evolutionary pressure to get smaller because of limits to
habitat area and food resources compared to the mainland. But
small-bodied species, because there is a decreased risk from predators
on islands, are emancipated from evolutionary constraints on their size.
Some endangered island species today include: the dwarf buffalo Tamaraw
on the Philippine island of Mindoro, 21% the size of its closest
mainland relative; the spotted deer of the Philippine Visayan islands of
Panay and Negros, 26% the size of its closest mainland relative; and
Jamaica's hutia, a rodent 4-1/2 times bigger than its closest mainland
relative.
Indonesia's island of Flores is a remarkable laboratory for the island
effect, also called "Foster's rule," based on observations by
mammalogist J. Bristol Foster in the 1960s. It once was home to a dwarf
elephant relative, giant rats and a giant stork, as well as a dwarf
human species - Homo floresiensis, nicknamed the "Hobbit," standing just
3-1/2 feet tall (106 cm) tall. The Hobbit disappeared about 50,000 years
ago, shortly after our species Homo sapiens reached Flores.
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A mounted skeleton of an extinct
Sicilian dwarf elephant, the size of a Shetland pony, is seen at
Museo Geologico “G. G. Gemmellaro” in Palermo, Sicily, Italy in this
undated handout photo. Dwarf elephants that lived in Sicily and
Cyprus were examples of the "island effect," a rule in evolutionary
biology describing how large-bodied species tend to downsize on
islands while small-bodied species upsize. Roberto Rozzi/Handout via
REUTERS
Islands are biodiversity hotspots. Although they cover less than 7%
of Earth's land area, they account for up to 20% of land species.
"Because of the island rule, you get all sorts of weird and
wonderful animals on islands, many of which are already extinct. Of
the still-extant species, islands harbor a large proportion of the
diversity of terrestrial species on the planet and about 50% of them
are at risk of extinction. It's incredibly depressing," said
paleoecologist and study co-author Kate Lyons of the University of
Nebraska-Lincoln.
The researchers documented an accelerating uptick in island
extinctions, beginning more than 100,000 years ago.
Our species has played a leading role through hunting, habitat
destruction, and introductions of diseases and invasive predators,
destabilizing pristine island ecosystems. Even the earlier arrival
of extinct human species like Homo erectus on islands coincided with
a doubling in extinctions.
"We always need to be cautious about stating true causality,
especially because there are usually many different things happening
at the same time," said biologist and study co-author Jonathan Chase
of the German Centre for Integrative Biodiversity Research.
"But our results show with pretty good certainty that extinction
rates on those islands increased dramatically after the arrival of
modern humans, which, at least historically, were often due to
overhunting," Chase added. "There might have only been a few hundred
dwarf elephants running around Cyprus when humans first got there,
and it didn't take long for them to disappear."
(Reporting by Will Dunham, Editing by Rosalba O'Brien)
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