The plateau pika (Ochotona curzoniae) is a keystone species for biodiversity on the Tibetan plateau

It is necessary to look at the big picture when managing biological resources on the Qinghai–Xizang (Tibetan) plateau. Plateau pikas (Ochotona curzoniae) are poisoned widely across the plateau. Putative reasons for these control measures are that pika populations may reach high densities and correspondingly reduce forage for domestic livestock (yak, sheep, horses), and because they may be responsible for habitat degradation. In contrast, we highlight the important role the plateau pika plays as a keystone species in the Tibetan plateau ecosystem. The plateau pika is a keystone species because it: (i) makes burrows that are the primary homes to a wide variety of small birds and lizards; (ii) creates microhabitat disturbance that results in an increase in plant species richness; (iii) serves as the principal prey for nearly all of the plateau’s predator species; (iv) contributes positively to ecosystem-level dynamics. The plateau pika should be managed in concert with other uses of the land to ensure preservation of China’s native biodiversity, as well as long-term sustainable use of the pastureland by domestic livestock. All correspondence to: Andrew T. Smith. Tel: xx.480.965.4024; Fax: xx.480.965.2519; E-mail: [email protected] plateau ecosystem offer little protection for nesting animals. The burrows constructed by the plateau pika offer breeding habitat for many species. Hume’s ground jay (Pseudopodoces humilis) and several species of snowfinch (Montifringilla adamsi, M. blanfordi, M. davidiana, M. ruficollis, M. tacazanowski) nest primarily in pika burrows (Prejevalski, 1876; Meyer de Schauensee, 1984; Feng, Cai & Zheng, 1986; Smith et al., 1990; Ma, 1995; Schaller, 1998). These birds are more abundant in areas inhabited by pikas (Ma, 1995). Similarly, Pere David’s snow finches (M. davidiana) and Isabelline wheatears (Oenanthe isabellina) regularly nest in the holes of Daurian pikas (O. daurica), an ecologically similar species that also occupies portions of the plateau (Smith et al., 1990). In addition, native lizards (Phrynocephalus vlangalii, Eremas multiocellata) use pika burrows for cover and as breeding sites. Loss of pikas, and thus the burrows they create, negatively impacts many species and reduces native biodiversity on the Tibetan plateau (Li, 1989; pers. obs.). Increased plant species richness Evidence for increased plant species richness caused by the burrowing activities of the plateau pika is indirect, because there are insufficient studies on this phenomenon in the Tibetan plateau ecosystem. However, a wide variety of studies on similar species on grasslands in other areas, including Asia, all indicate that the surface disturbance caused by burrowing animals commonly increases plant species richness compared to areas without burrowing animals (Formosov, 1928; Huntly & Reichman, 1994). Total plant species diversity on the American prairie is greatest in areas occupied by prairie dogs (Whicker & Detling, 1988; see also Stapp, 1998; Kotliar et al., 1999). On the Mongolian steppe local floral diversity is enhanced by the burrowing of Daurian pikas (some shrub plants only grow on pika burrows; Dmitriev, 1985; Smith et al., 1990). Certain plants (Euphorbia altaica, Artemesia spp. and some crucifers) grow only on the burrows of Pallas’s pika (O. pallasi pricei; Smith et al., 1990). At the International Symposium on the Qinghai–Tibet Plateau held in Xining in July 1998, the European Union-funded Qinghai Livestock Development Project stated clearly that more ‘weeds’ are present in areas with plateau pikas than in the surrounding grassland, thus indicating an increased plant diversity. However, it will take long-term controlled experiments in areas that are not overgrazed to evaluate the full relationship between plateau pikas and plant diversity (Stapp, 1998; Kotliar et al., 1999). Pikas serve as prey for many native wildlife species Most predatory animals on the Tibetan plateau rely heavily on pikas in their diet (Prejevalski, 1876; Smith et al., 1990; Schaller, 1998). Across much of the plateau, the pika is the dominant small mammalian herbivore. Wooly hares (Lepus oiostolus) are encountered very rarely, and Himalayan marmots (Marmota himalayana) are scarce and patchily distributed. Only the fossorial zokor (Myospalax baileyi), a species also subject to control, can be found at high densities, but zokor colonies are also patchily distributed and encountered infrequently. Pikas are not only the most abundant source of food for predators during the summer, but as pikas do not hibernate, they become almost the sole source of food for many predatory species during winter. When pikas are exterminated regionally this important source of food disappears, starving predators and resulting in a loss of local biodiversity. We have driven across vast stretches of the plateau without seeing any raptors soaring in the sky – more often than not these are the areas void of pikas due to prior poisoning campaigns. Conversely, the presence of raptors generally indicates areas of healthy pika populations. Populations of steppe polecat (Mustela eversmanni) on the plateau (like their counterpart in North America, the black-footed ferret (M. nigripes) which preys on prairie dogs) are linked to the dynamics of pika populations (Nekipelov, 1954; Schaller, 1985; Smith et al., 1990). In North America control of prairie dogs has resulted in the near extirpation of the black-footed ferret, which only now is being rescued from extinction using expensive intervention (B. Miller, Reading & Forrest, 1996). Similarly, other small mammals such as weasels (Mustela altaica, M. eversmanni), foxes (Vulpes ferrilata, V. vulpes), and Pallas’s cat (Otocolobus manul) rely heavily on plateau pikas for food (Smith et al., 1990; Schaller, 1998). Many larger mammalian predators such as wolves (Canis lupis), snow leopards (Uncia uncia) and brown bears (Ursus arctos) also prey on animals as small as the plateau pika (Schaller, 1998). Snow leopards largely specialize on big game, and pikas act only as a buffer species (Schaller, 1998). However, pikas comprise over 50% of the diet of wolves in some areas (Schaller, 1998), and brown bears appear to be particularly reliant on pikas for food. One study in the Chang Tang region found that almost 60% of the diet of brown bears was pikas (Schaller, 1998). During his 1893–1896 expedition to the Tibetan plateau, Kozlov found 25 pikas in the stomach of one bear, and when Przewalski secondarily defined the Tibetan form, he called it U. lagomyiarius or ‘bear pika-eater’ (Smith et al., 1990). Most large predatory birds on the Tibetan plateau (golden eagles, Aquila chrysaetos; upland buzzards, Buteo hemilasius; saker falcons, Falco cherrug; goshawks, Accipiter gentilis; black kites, Milvus migrans; little owls, Athene noctua) depend upon pikas as a food source. Schaller (1998) determined that 90% of pellets under the nest of a saker falcon contained pika remains, as did all of the pellets beneath the nest of an upland buzzard. The similar Daurian pika has been shown to comprise the following percentages of the diet of avian predators in southeast Transbaikalia: steppe eagle (Aquila nipalensis), 62%; upland buzzard, 17%; eagle owl (Bubo bubo), 73%; and saker falcon, 22% (Peshikov, 1957, 1967). 236 A. T. SMITH & J. M. FOGGIN