Species composition and size structure of frogs preyed by the Iriomote cat Prionailurus bengalensis iriomotensis

Abstract

Most species of small felids exclusively prey on groundliving mammals such as rodents (Kruuk 1982). Leopard cats Prionailurus bengalensis are also known as typical mammalian predators (Sunquist and Sunquist 2002), except for the Iriomote cat Prionailurus bengalensis iriomotensis, a subspecies of leopard cats endemic to Iriomote Island (284 km, 24°20'N, 123°49'E) in the southernmost part of the Ryukyu Archipelago, Japan. The cat had been long considered a separate species due to morphological differences with other small felids of Southeast Asia (Imaizumi 1967; Leyhausen and Pfleiderer 1999). Recently, their specific taxonomical distinction has been questioned by molecular methods (Masuda et al. 1994; Johnson et al. 1999) but despite this, the feeding ecology of the Iriomote cat remains unique among the cat family as they do not only prey upon mammals but also a variety of animals, such as birds, reptiles, frogs, and insects (Sakaguchi and Ono 1994; Watanabe et al. 2003). The variety of this cat’s diet may be an illustration of the optimal foraging theory in which animals should sample a variety of prey types and/or sizes to maximize their energy intake (Stephens and Krebs 1986). For instance, the Iriomote cat selectively preys on large-sized skinks during the warm season when skinks are abundant (Sakaguchi and Ono 1994). To get a better understanding of the feeding ecology of the Iriomote cat, its principal prey should be evaluated in detail with regard to species identification and size distribution. Preying on ground-living birds and reptiles has already been examined (Sakaguchi and Nishihira 1988; Sakaguchi and Ono 1994) but examination of the cat preying on frogs has not yet been carried out due probably to the difficulties in identifying the anuran species in fecal samples. Here, we developed a technique to identify species and to estimate body sizes of frogs found in the feces of cats. Following identification, the feeding pattern of Iriomote cats was considered with regard to species and size composition of frogs eaten.