Reduced predator species richness drives the body gigantism of a frog species on the Zhoushan Archipelago in China

Abstract

Summary1. 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.

Convergence in reduced body size, head size, and blood glucose in three island reptiles

“…More research is needed to explore the interaction between corticosterone, glucose, and predation. However, island species experiencing predatory release tend to exhibit gigantism (e.g., Adler & Levins, 1994;Li et al, 2011;Michaux, De Bellocq, Sarà, & Morand, 2002;Olson & Hearty, 2010;Palkovacs, 2003), whereas all three reptiles in our study exhibit dwarfism. This suggests that both the reduction in body size as well as circulating blood glucose levels are likely a consequence of resource restriction rather than predatory release.…”

The evolutionary ecology of dwarfism in three‐spined sticklebacks

“…; Herczeg, Gonda & Merila ; Li et al . ). In our study, the large variation in trout size between populations shows that this may be inadequate to fully understand the contributions of variation in predation to evolution of ‘prey’.…”

“…; White & Searle ; Li et al . ) and should help the design of future experiments. Observational studies should measure all of the different factors that are hypothesised to affect body size.…”

“…However, the factorial experiments that are necessary should ideally be multigenerational and are therefore difficult and time-consuming to carry out for anything other than the shortest-lived species. Observational evidence obtained from thorough ecological studies can provide insights into the relationships between variation in body size across taxonomic units and systematically quantified environmental variation (Michaux et al 2002;White & Searle 2007;Li et al 2011) and should help the design of future experiments. Observational studies should measure all of the different factors that are hypothesised to affect body size.…”

Global and endemic Asian lineages of the emerging pathogenic fungus Batrachochytrium dendrobatidis widely infect amphibians in China

“…Each tissue sample from toe clips and mouthparts was preserved separately in 70% EtOH in 2‐ml screw‐cap microcentrifuge tubes then stored at −20 °C in the laboratory. We determined whether a site had been invaded by bullfrogs or clawed frogs by surveying all accessible water bodies in each site for three consecutive nights with line transects (Li et al. , 2011a).…”