Biohistory Journal,Winter, 2005

Research: Index > The ecological system of Iriomote Island from the perspective of the wild cat

The ecological system of Iriomote Island from the perspective of the wild cat

Masako Izawa Faculty of Science, University of the Ryukyus

Located in the moist subtropical belt, the Ryukyu Islands have many distinct types of islands or island groups that stretch from north to south. The Yaeyama Islands are a mountainous group at the extreme southern end of the archipelago. Iriomote Island is one of them. The Iriomote cat, the only carnivore native to the Ryukyu Islands, inhabits this island. About 100 of these animals have been identified since their discovery 40 years ago, and their protection is an urgent issue. Why are wild cats only on Iriomote Island? Why are there so few of them? Iriomote Island has a rich ecosystem, but life on island presents difficulties for the cats. The land area of the island is small for carnivorous animals, and there are no rabbits or mice, which are the staple of the feline diet. We know that the Iriomote cat is a descendant of the leopard cat, which crossed over from the continent about 200,000 years ago, but the survival of the Iriomote cat on Iriomote Island is an enigma. I have studied the activities of the feline family, and I began a survey of their feeding habits and activities to solve this enigma. What I discovered was the way of life of the wild cats that featured survival skills in the Iriomote ecosystem.

I collected samples of Iriomote cat dung and studied its diet from the undigested food. As a result of this study, I found that without picky eating, their diet consisted of a wide range of animal classifications, including such mammals as the fruit bat and the black rat (non-native species); such birds as the rail; reptiles and amphibians, such as lizards and frogs; and arthropods, such as the cricket and the crab. It was particularly interesting that it ate frogs, which ordinary cats are believed not to eat. When I traced its activities, I found that in contrast to its designation as a wild cat, the Iriomote cat often appeared in low-lying coastal areas or areas next to wetlands. It showed no hesitation about swimming in rivers. This ability to utilize an abundant water environment that incorporates mangrove forests, swamps, and grassy plains is the primary reason it has been able to survive on a small island without rats.       The number of animals living here in the 200,000 years since the wild cat crossed over to Iriomote Island in this isolated environment is estimated to be a few hundred at the most. The genetic diversity of the Iriomote cat is remarkably low, but that is the result of the survival of individuals adapted to the bountiful and stable Iriomote environment. On the other hand, the current destruction of this bounty holds the danger that the Iriomote cats could quickly disappear. It is just a small change from several hundred to one hundred, but it sounds the alarm for the island’s ecosystem.

Masako Izawa     After being awarded a Doctor of Sciences degree from Kyushu University in 1984, Izawa has worked at Kyushu University and the Kitakyushu Museum of Natural History. Since 1991, she has been an associate professor in the Department of Chemistry, Biology and Marine Science at the Faculty of Science, University of the Ryukyus.

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