Abstract
Embryonic mortality and clutch size of the foam-nesting treefrog Rhacophorus arboreus were observed in early summer of 2000 and 2001 at a small pond in a secondary forest on the campus grounds of Tokyo Metropolitan University. A total of 24 foam nests were monitored from just after spawning. When hatchlings emerged, the foam nests were collected and examined for embryonic mortality and clutch size. Embryonic mortality, averaging 0.233 (0.036-0.616, SD=0.173), varied markedly among nests. Logistic regression showed that the date of spawning had a significant effect on embryonic mortality: the nests constructed late in the season suffered higher mortality. Clutch size varied from 272 to 872 (x=522.1, SD=134.0). Multiple regression analysis showed that year and date of spawning had no significant effect on clutch size. A significant correlation was detected between clutch size and height of the nesting position (r=-0.563, P=0.004): those nests constructed higher above the pond water tended to have smaller clutches. Factors affecting egg mortality and clutch size are discussed.
