The effects of food and density on growth and metamorphosis in larval wood frogs (Rana sylvatica) from central Labrador

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Abstract
Two experiments were performed on Rana sylvatica tadpoles from central Labrador to test for effects of food and density on growth and metamorphosis. In an experiment examining for the presence of diffusible growth inhibitors, one group of tadpoles was given water treated by adding a high density of sibling tadpoles, and another group was given filtered lake water. No diffusible growth inhibitors existed in this population, as body weight measured weekly, wieght at metamorphosis, and duration of larval stage did not between control and treated groups. In a food-density experiment, effects of food and larval density were examined by subjecting tadpoles at four different densities to four food levels, creating a 4 .times. 4 food-density matrix. Food and density both affected growth rate, weight at metamorphosis, and duration of larval stage. Socially governed negative density-dependent interactions are either nonexistent in northern populations, or were completely masked by slight positive effects of grouping. Results suggest that northern larvae differ in life-history strategy from southern populations, and the possibility of overwintering in immature stages of high-latitude populations is discussed.