Aim: Phenotypic shifts are commonly observed when animals face insular habitat change and may reflect ongoing stresses on individuals. However, the generality and the driving processes of this ‘island rule’ remain equivocal, notably in amphibians. Here, we investigate both morphological and dietary shifts in a frog using a mosaic of human-created islands to assess the potential operating mechanisms underlying these phenotypic responses.

Location: Thousand Island Lake, China.

Taxon: The Chinese piebald odorous frog, Odorrana schmackeri.

Results: We found insular dwarfism in female but not male frogs. Meanwhile, insular females also had smaller gape widths after accounting for snout-vent lengths (SVLs) than mainland females. According to SEMs, resource availability had a direct positive effect on body size. Finally, diet composition differed between island and mainland populations, but only in females. Males and females on islands exhibited greater overlaps in diet.

Main conclusions: In contrast with most studies in amphibians, we found insular dwarfism rather than gigantism in females. The smaller gape width after accounting for SVL in insular females suggests potential changes in prey utilization or food availability on these human-created islands. This notion is further supported by the differentiation of diet composition between island and mainland females. The higher diet overlap between sexes implies stronger intersexual competition for food resources after habitat fragmentation. Overall, we found shifts in morphology and diet in frogs which may implicate the influence of habitat fragmentation and underscores the need to consider intersexual differences when assessing responses of species to anthropogenic disturbances.

We compared body size between insular and mainland populations and between sexes. We examined the potential underlying mechanisms regarding body size shifts using structural equation modelling (SEM). Finally, we analyzed changes in diet composition and compared intersexual diet overlap between island and mainland sites.

Please see the details of the data in the README.text file.