COMPETITION BETWEEN COMMON FROG, RANA-TEMPORARIA, AND NATTERJACK TOAD, BUFO-CALAMITA, TADPOLES - THE EFFECT OF COMPETITOR DENSITY AND INTERACTION LEVEL ON TADPOLE DEVELOPMENT

The effect of common frog (Rana temporaria) tadpole density and level of interspecific interaction on the development of natterjack toad (Bufo calamita) tadpoles was studied using a replicated pond experiment. Growth, mass at metamorphosis, date of metamorphosis, and survival were used as measures of the response to interspecific competition. High densities of R. temporaria tadpoles resulted in slower growth, smaller size at metamorphosis, prolonged development and reduced survival of B. calamita tadpoles. Under conditions of full interaction with R. temporaria (both species free-swimming), and partial interaction with R. temporaria (physical contact between species prevented by an enclosure), B. calamita performed less-well than controls raised without R. temporaria. B. calamita interacting partially with R. temporaria fared slightly better than those interacting fully with R. temporaria. B. calamita raised in pond water previously conditioned by R. temporaria tadpoles did not differ from controls raised in unconditioned water. When B. calamita were raised without R. temporaria, later metamorphs emerged at a larger size than the early metamorphs. This relationship was reversed in B. calamita raised with R. temporaria under conditions of both full and partial interaction. Interspecific competition can occur between these two species in the absence of physical interactions. Under such conditions competition could be mediated by depletion of suspended food particles, nutrient depression, or labile growth inhibitors.