Body Size Affects the Predatory Interactions between Introduced American Bullfrogs (Rana catesbeiana) and Native Anurans in China: An Experimental Study YANPING WANG, 1,2 ZHONGWEI GUO, 1 CHRISTOPHER A. PEARL, 3 AND YIMING LI 1,4 1 Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, 25 Beisihuanxi Road, Haidian, Beijing 100080, People’s Republic of China 2 Graduate School of the Chinese Academy of Sciences, 19 Yuquan Road, Shijingshan, Beijing 100039, People’s Republic of China 3 United States Geological Survey, Forest and Rangeland Ecosystem Science Center, 3200 Southwest Jefferson Way, Corvallis, Oregon 97331, USA ABSTRACT.—Introduced American Bullfrogs (Rana catesbeiana) have established breeding populations in several provinces in China since their introduction in 1959. Although Bullfrogs are viewed as a potentially important predator of Chinese native anurans, their impacts in the field are difficult to quantify. We used two experiments to examine factors likely to mediate Bullfrog predation on native anurans. First, we examined effects of Bullfrog size and sex on daily consumption of a common Chinese native (Rana limnocharis). Second, we examined whether Bullfrogs consumed similar proportions of four Chinese natives: Black-Spotted Pond Frog (Rana nigromaculata), Green Pond Frog (Rana plancyi plancyi), Rice Frog (R. limnocharis), and Zhoushan Toad (Bufo bufo gargarizans). We found that larger Rana catesbeiana consumed more R. limnocharis per day than did smaller R. catesbeiana, and that daily consumption of R. limnocharis was positively related to R. catesbeiana body size. When provided with adults of four anurans that differed significantly in body size, R. catesbeiana consumed more individuals of the smallest species (R. limnocharis). However, when provided with similarly sized juveniles of the same four species, R. catesbeiana did not consume any species more than expected by chance. Our results suggest that body size plays an important role in the predatory interactions between R. catesbeiana and Chinese native anurans and that, other things being equal, smaller species and individuals are at greater risk of predation by R. catesbeiana. The American Bullfrog, Rana catesbeiana, is considered one of the 100 worst invasive alien species in the world (IUCN, 2003). Native to eastern North America, the Bullfrog has been widely introduced to various regions of the world (Bury and Whelan, 1984; Lever, 2003). Adult Bullfrogs are efficient, generalist preda- tors that may affect other amphibians through direct predation (Bury and Whelan, 1984; Werner et al., 1995). Establishment of Bullfrogs and coincident declines in native anurans has led to the hypothesis that Bullfrog predation may be affecting native populations (Moyle, 1973; Hayes and Jennings, 1986). Predation impacts of Bullfrogs are hard to quantify in the field for several reasons, including the likelihood that interactions are condensed in time and the difficulty of extrapolating diet composition into conclusions relevant at a pop- ulation scale (Kupferberg, 1997). Since 1959, Bullfrogs have been introduced to most provinces of mainland China and have established breeding populations in Yunnan, Sichuan, Shanxi, and Zhejiang Provinces including the Zhoushan archipelago (He, 1998; Li and Xie, 2004; Wu et al., 2004; Li et al., 2006). The Bullfrog is much larger than any native anuran in China (Fei, 1999) and is known to consume at least four of 10 native species in the Zhoushan archipelago: four Zhoushan Toads (Bufo bufo gargarizans), 14 Rice Frogs (Rana limnocharis), five Black-Spotted Pond Frogs (Rana nigromaculata), and one Zhenhai Brown Frog (Rana japonica) were consumed by 356 American Bullfrogs (Wu et al., 2005; Wang et al., 2006). However, their impacts as predators on native anurans in China, as in most invaded regions, are difficult to extrapolate into popula- tion effects in the field. Estimating food consumption is central to defining the ecological role of predators (Body, 2002) and, thus, provides an important way to quantify the predatory impacts of Bullfrogs on native anurans. Factors influencing daily con- sumption by Bullfrogs on native anurans may be helpful in understanding and predicting Bullfrog effects as they join anuran communities in their expanding global range. The first objective of this study was to quantify the 4 Corresponding Author. E-mail: liym@ ioz.ac.cn Journal of Herpetology, Vol. 41, No. 3, pp. 514–520, 2007 Copyright 2007 Society for the Study of Amphibians and Reptiles