Iriomote’s Endemic Cat
Although islands are known for the high degree of endemism found amongst their flora and fauna, there are relatively few examples of endemic carnivores. This is largely because islands tend to be depauperate of large mammalian predators in general, much less exclusive endemics (although see my recent Scientific American guest post for an intriguing exception to the rule about carnivore diversity on islands). The long-term prognosis for an endemic species is usually cloudy; extinction rates for these organisms are high, and even moreso when said species is a medium- to large-sized mammal—due to the fact that it likely has demanding dietary and spatial requirements.
The best-known example of an endemic insular carnivore is probably the Channel Island fox, Urocyon littoralis, which is comprised of six subspecies found only on a single island chain off the coast of California. This species is one of the most endangered carnivores in the world, and is, notably, also the only extant insular canid. There has actually been a parade of endemic canids found on islands in the past: during the Pleistocene we had Cynotherium in Corsica, and Megacyon and Bececyon in Java. In historical times, the Japanese wolf, Canis hodophilax roamed several islands of Japan (see previous post on this species here), and the Falkland Islands wolf ( Dusicyon australis ) inhabited the Falkland Islands off the coast of South America. The extinction rate and turnover for island species tends to be higher than their mainland counterparts, however, and that of endemic island species is even higher still (Frankham 1998). Unsurprisingly, nearly every one of these insular canids has succumbed to extinction, leaving U. littoralis as the only species out of the 35 extant members of the family Canidae that exists as an island endemic.
So there have been, and still are (albeit barely) endemic canids found on island chains. But canids are often broad dietary generalists, able to exist on a variety of items ranging from small vertebrates to, in the case of the Channel Island fox, cacti and plants of the toxic sumac family. What about more strict meat-eaters (known as hypercarnivores, see Van Valkenburgh 1988), such as cats?
Cats tend to have a narrower dietary repertoire than their more omnivorous canid counterparts. They don’t diet-switch as often, and are less likely to consume plant items such as fruits and fleshy stems. In other words, they are pickier, and that does not bode well in areas such as islands, which are limited in diversity of resources as well as quantity. Also, excluding lions, cats have do not have the same degree of group sociality as canids. This means they often do not tolerate much spatial overlap. This results in lower population densities and the need for more space than a canid species would to accomodate a given number of individuals. Thus, it stands to reason that cats would be even less likely to exist as island endemics than canids, which themselves do not seem to be very good at persisting exclusively on islands. Not a promising picture, is it?
Unlikely, yes, but exist they do. The Iriomote cat, Proailnurus iriomotensis, is considered to be a strikingly basal member of the Felidae, and occurs exclusively on the eponymous Japanese island of Iriomote. This tiny island has an area of only of 292 sq km, and the cat inhabits only a small part of even that limited space, existing mainly on the lowlands of the coast and escewing the interior mountain habitats (Izakawa 2008). Unfortunately, the humans of Iriomote have largely the same preferences for their croplands. The island was largely uninhabited until after World War II, and is currently home to around 2,000 people, a single paved road, no airstrips, lots of pineapple plantations, and the world’s only population of this fascinating felid.
Some claim that the Iriomote cat is actually a subspecies of the leopard cat, Felis bengalensis (which has itself been shuffled back and forth between two genera, Felis and Prionailurus), yet it bears some significant phenotypic differences, and the taxonomy has been long-debated. Researchers have posited that this is a highly basal taxa, which is the closest extant representative of the common ancestor of three genera, Prionailurus, Profelis, and Pardofelis (Leyhausen and Pfleiderer 1999). It is thought that the Iriomote cat diverged from the leopard cat about 200,000 ago, when the land mass that is now Iriomote separated from other islands in the Ryuku chain (Masuda et al. 1994). When the cat was first discovered in 1965, it was classified as a monospecific genus, Mayailurus, but since then there has been the common taxonomic tug-of-war between scientists that think it is a subspecies and those that think it is a distinct species, subgenus, or genus all to itself. Whatever the answer to that question, there is no doubt that it is a unique taxonomic entity of high conservation concern.
Describing this species as being of “high conservation concern” may not be emphatic enough. This is one of the rarest carnivores on the planet, with a total population of fewer than 100 animals that exist as a single subpopulation, meaning that if something catastrophic (a tsunami, for example, or an epidemic disease) happens to this one set of cats, the Iriomote cat is gone forever. Also important to keep in mind is that total population estimates rarely reflect the actual number of reproductive individuals (known as the effective population), so the actual number of animals capable of propagating the species is probably far lower.
This species has a notably basal appearance relative to most other extant felids: its “primitive” features include short legs, an elongate body, and a short, bushy tail. The coat pattern features spots that gradually blur into longitudinal bands, and it has rounded ears. In addition, its claws are not fully retractile (similar to the fishing cat, Prionailurus viverrinus, and flat-headed cat, Prionailurus planiceps ), and it also lacks an anterior upper premolar.
This diminutive cat (it is about the same size as a house cat, 5-10 pounds) also has some interesting and unique behaviors befitting an island endemic, such as its habits of paddling through mangrove forests in search of food and stalking crabs on the island’s sandy shores. Fruit bats account for over 16% of its diet (Yasuma 1981), and it also consumes many other vertebrates, both volant and terrestrial. As far as the crowding issue goes, these cats are solitary, yet male home ranges have been found to overlap with neighboring cats of both sexes. Female home ranges typically do not overlap with one another.
The Iriomote cat is protected by both the IUCN and has been listed as endangered on Japan’s national Red List since 2002, although deforestation for agriculture continues to threaten the outlook for this species. Efforts are being made, however, to use the species as a way to draw tourists to the island, in which case it is in the economic interest of the local inhabitants to keep it around. Whether this plan will prove effective remains to be seen, but in the mean time, the Iriomote cat represents a taxa that is highly unique both evolutionarily and ecologically, and it will be a great loss if it disappears due to further habitat destruction.
Frankham, R. 1998. Inbreeding and extinction: island populations. Conservation Biology 12: 665-675.
Izawa, M. 2008. Prionailurus bengalensis ssp. iriomotensis. In: IUCN Red List of Threatened Species. Version 2010.4.
Leyhausen, P. and M. Pfleiderer.1999. The systematic status of the Iriomote cat (Prionailurus iriomotensis Imaizumi 1967) and the subspecies of the leopard cat (Prionailurus bengalensis Kerr 1792). Journal of Zoological Systematics and Evolutionary Research 37: 121-131.
Masuda, R., Michihiro, C., Shinyashiki, F. and Bando, G. 1994. Molecular phylogenetic status of the Iriomote Cat Felis iriomotensis inferred from mitochondrial DNA sequence analysis. Zoological Science 11:597-604.
Mochizuki, M., M. Akuzawa, and H. Nagatomo. 1990. Serological survey of the Iriomote cat (Felis iriomotensis) in Japan. Journal of Wildlife Diseases 26: 236-245.
Van Valkenburgh, B. 1988. Trophic diversity in past and present guilds of large predatory mammals. Paleobiology 14: 155-173.
Yasuma, S. 1981. Feeding behaviour of the Iriomote cat (Prionailurus iriomotensis Imaizumi, 1967). Bulletin of Tokyo Univ. Forests 70:81-140.
Photo credits to Makoto Yokotsuka and Yosoko Izawa