Inter- and Intraclutch Competition among Oophagous Tadpoles of the Taiwanese Tree Frog, Chirixalus eiffingeri (Anura: Rhacophoridae)

We studied the dynamic interactions within and between different hatching cohorts of tadpoles of Chirixalus eiffingeri reared in pools in bamboo stumps at the Experimental Forest of the National Taiwan University at Chitou, Taiwan, during 1997 and 1998. In a 2 × 3 factorial experiment (Experiment I), we assessed the effects of older tadpoles (none, 10 medium, or 10 large tadpoles) on the growth, survivorship, and metamorphosis of younger, small tadpoles in two densities (10 or 20 tadpoles). In most cases, tadpoles of both older size classes significantly affected the growth, survivorship, survival to metamorphosis, the length of larval period, and mass at metamorphosis of younger tadpoles. The effects of medium and large tadpoles on small tadpoles were similar. An increase in the clutch size of younger tadpoles prolonged the length of larval period but did not affect the mass at metamorphosis or survival to metamorphosis. In Experiment II, we studied the effects of the number of older tadpoles on the growth, survivorship, and metamorphosis of younger tadpoles. There were four treatments: 20 younger tadpoles (20S), 30 younger tadpoles (30S), 10 younger and 10 older tadpoles (10S 10L), and 10 younger and 20 older tadpoles (10S 20L). Older tadpoles decreased the growth and survival of younger tadpoles. An increase of the abundance of older tadpoles, from 20 to 30, affected the survival to metamorphosis of younger tadpoles. All younger tadpoles in the 10S 20L treatment died. Experiments I and II demonstrated that the number, but not the developmental stage, of older tadpoles had detrimental effects on the growth and development of the younger tadpoles, which has important implications for the reproductive strategies of female frogs. The maternal provisioning of eggs for nutrition of C. eiffingeri is energetically expensive; thus, the time when the second clutch of eggs is laid is critical to the overall reproductive success of female frogs. Female frogs should lay a second clutch of eggs only after the older tadpoles are low in number, which may reduce intraspecific competition between the two cohorts of tadpoles.