[show abstract][hide abstract] ABSTRACT: 1. Shifts in the body size of insular vertebrates have been an interesting theme in ecological and evolutionary studies. Four primary factors, including predation pressures, resource availability, inter-species competition and immigrant selection, have been proposed to explain the trend in insular body size. Life-history theory predicts that body size, average age, the proportion of old-aged members and the density of insular populations are negatively correlated with predator species richness, and that body size and population density are positively related to resource availability. The niche expansion hypothesis argues that a positive relationship is expected to exist between insular body size and prey size, which varies in response to extinction due to small or large competitors. The immigrant hypothesis predicts that insular body size is positively correlated with distance to the mainland. 2. We tested these hypotheses by using populations of rice frogs Rana limnocharis on 20 islands in the Zhoushan Archipelago and two sites of nearby mainland China. 3. The body size (snout-vent length) of rice frogs on half of the islands was larger before and after the variable of age was controlled for; rice frog density and prey availability was higher and prey size was larger on most of the islands as compared to the two mainland sites. On the islands, the body size and other features [e.g. average age, the proportion of old-aged frogs (ages 3 and 4) and density] of the rice frogs were negatively associated with predator species richness; female body size and other features were positively associated with prey availability. The inference of multivariate linear models based on corrected Akaike Information Criterion (AIC(c) ) showed that the relative importance of predator species richness on body size and each of the other features was larger than that of prey availability, prey size and distance to the mainland. In addition, the parameters for predator species richness were all negative. 4. The results provided strong support for the life-history theory of predation pressures, but weak evidence for the life-history theory of prey availability, the niche expansion or the immigrant hypothesis. The reduced predator species richness was a dominant factor contributing to the body gigantism of rice frogs on the islands.
Journal of Animal Ecology 01/2011; 80(1):171-82. · 4.84 Impact Factor
[show abstract][hide abstract] ABSTRACT: Bullfrogs (Rana catesbeiana) are listed as one of the 100 worst invasive alien species in the world. They are generalist predators and thus may affect
native species through predation. In previous studies, the food contents of bullfrogs were mostly examined at a single site.
In the present study, the diet composition of post-metamorphic bullfrogs on eight islands (Daishan, Liuheng, Xiushan, Fodu,
Taohua, Xiashi, Cezi, and Putuoshan) in the Zhoushan Archipelago, Zhejiang Province of China, were examined by using the stomach
flushing method from June 30 to August 11 in 2005. A total of 391 individual frogs were measured, including 113 adults and
278 juveniles. The analysis of the stomach contents shows that, for adult bullfrogs, the most important prey (by diet volume)
overall were Decapoda, Coleoptera, Odonata, Mesogastropoda, Raniformes, and Cypriniformes. For juvenile bullfrogs, these were
Decapoda, Coleoptera, Cypriniformes, Odonata, Orthoptera, Hymenoptera, Lepidoptera larvae, Mesogastropoda, and Raniformes.
Moreover, the prey size and diet volume increased with the body size of both adult and juvenile bullfrogs. The diet composition
of primary preys of bullfrogs was significantly different among the islands. The results indicate that bullfrogs exert different
predatory influences on native fauna at different sites and that bullfrogs are generalist predators with extensive ecological
impacts on native fauna.