Why Are Larval Fejervarya kawamurai Scarce in the Paddies Where Larvae of Other Frogs Are Abundant? Experimental Insights

Abstract

Although Fejervarya kawamurai is a common frog in the paddies of western Japan, their larvae seem to be scarce in the paddies where larvae of Hyla japonica and Pelophylax nigromaculatus are abundant. To examine the cause of this phenomenon, we surveyed the reproductive season of these three species at two sites with different irrigation schedules using an automatic recording system. In addition, we conducted several experiments to test three possible explanations; (1) maternal avoidance from P. nigromaculatus larvae in the selection of oviposition site, (2) predation on F. kawamurai eggs by P. nigromaculatus and the larvae of other species, and (3) negative interactions of P. nigromaculatus larvae on the larvae of F. kawamurai. In paddies flooded throughout the year, calling of H. japonica and P. nigromaculatus started far earlier than in F. kawamurai, whereas in paddies irrigated in mid-May, these three species started calling simultaneously. We found significant predation pressures on F. kawamurai eggs from larvae of H. japonica, Rana japonica, P. nigromaculatus, P. porosus brevipodus, Glandirana rugosa, F. kawamurai, and Rhacophorus schlegelii, whereas no significant predation pressures from larvae of B. japonicus was detected. We found no evidence of maternal choice by F. kawamurai for oviposition sites and no effects of P. nigromaculatus larvae on sympatric larvae of F. kawamurai. Our results suggest the possibility that the mortality rate of F. kawamurai eggs might increase through predation at paddies where H. japonica and P. nigromaculatus start oviposition earlier than does F. kawamurai.