Among the pond-breeding frogs found in rice paddy area, Rana porosa brevipoda is particularly decreasing rapidly. The threats for the species were considered loss and changes of rice paddy environments. Because the species need wet environment all around a year, the loss of such environment by improvements of the rice paddy drainage was considered the main reason. For the species conservation, creating refuge biotope, such as ponds, was suggested. However, there was no study verified the functions of such biotope in maintaining the frog population.

We conducted surveys in lowland rice paddy area in Shiga. Study sits were two rice paddy areas and two constructed refuge biotopes. We captured frogs as many as possible and recorded sex and snout-vent length (SVL), in 2010 and 2011. Based on the data, we compare the population characteristics, such as size structure, sex ratio and analyzed the survivorship of different sizes by drawing size-specific survivorship curve.

Overall, more females than males were found, and the average and maximum size of females were larger than those of males. In the rice paddy areas, we found more juveniles than in the refuge biotopes but less large adult frogs. The rice paddy areas played important role as breeding sites, and the refuge biotopes were compensate for the lack of wet environment especially during summer and winter.