DENSITY REGULATION IN TADPOLES OF RANA TEMPORARIA: A FULL POND FIELD EXPERIMENT

Abstract

Tadpole density dependence has repeatedly been studied in laboratories and mesocosms, but rarely in natural ponds. The present study manipulated density in three ponds; each pond was divided into one low density section and one high density section. The experiment was run for eight years, switching density treatments within ponds among years. This experimental design cannot definitively separate the experimental density effects from certain lag effects. This problem is discussed. Nonetheless, in all ponds tadpole survival was affected by the density manipulation. The reduced survival of larvae at high density was most pronounced in the pond with the overall highest density. In this pond, the density-dependent mortality almost offset the original, experimental, density difference between sections. Effects on tadpole and metamorph size and development rate were found in those cases in which density-dependent mortality was weak and treatment effects on density persisted to the later stages of tadpole development. However, even if significant, these were generally of small magnitude compared to the variation among ponds and years. I suggest that different modes and degrees of regulation among populations of one species of frog are to be expected, not only due to variation in pond quality but also due to variation in the surrounding terrestrial habitat. This may determine the balance between tadpole and adult population regulation.