Dwarf elephants? Giant rats? Strange high-risk island creatures

Islands make small animals giant and giant animals shrink, but these unique species are endangered

A dwarf elephant the size of a pony once roamed the Mediterranean island of Cyprus. In the Antilles, a giant mouse-like rodent weighed over 400 pounds and rivaled the size of the black bear.

These are just two examples of the “island effect,” a rule of evolutionary biology that describes how large species tend to shrink on islands while small species grow. Island dwarfs and giants include miniature hippos, buffalo and wolves, which have long faced a high risk of extinction. according to a new study published in the journal Sciencethat risk is intensifying, putting some of Earth’s most unique creatures at risk.

Focusing on island mammals, researchers from the Museum of Natural History at Martin Luther University in Halle-Wittenberg (Germany) examined 1,231 existing and 350 extinct species over the past 23 million years. The greatest risk of extinction was seen among species that experienced more extreme changes in body size compared to their continental relatives. The arrival of humans on the islands has increased extinction rates by more than tenfold.

Some island species currently threatened are: the tamaraw dwarf buffalo, from the Philippine island of Mindoro, 21% larger than its closest mainland relative; spotted deer from the Philippine islands of Panay and Negros, 26% larger than its closest mainland relative; and the Jamaican hutia, a rodent four and a half times the size of its closest mainland relative.

The island of Flores, Indonesia, is a remarkable laboratory for the island effect, also called “Foster’s rule”, based on observations by mammologist J. Bristol Foster in the 1960s. It was home to a dwarf relative of the elephant, giant rats and a giant stork, as well as a dwarf human species: Homo floresiensis, nicknamed “Hobbit”, only 106 cm tall. The Hobbit disappeared about 50,000 years ago, shortly after our species, Homo sapiens, arrived on Flores.

The islands are biodiversity hotspots. Although they cover less than 7% of the earth’s surface, they are home to up to 20% of terrestrial species, and around 50% of them are in danger of extinction. Researchers have documented an accelerated increase in island extinctions starting more than 100,000 years ago. Humans, and even our ancestors, are behind this catastrophe.

Our species has played a leadership role through hunting, habitat destruction, and the introduction of disease and invasive predators, destabilizing pristine island ecosystems. Even the earlier arrival on islands of extinct human species, such as Homo erectus, coincided with a doubling of extinctions.


Dwarfism and gigantism drive human-mediated extinctions on islands

Photo: By Ninjatacoshell – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=5644644

Recent Articles

Related News

Leave A Reply

Please enter your comment!
Please enter your name here