Density Effects on the Survival, Growth Rate, and Metamorphosis of Rana Tigrina Tadpoles

Rana tigrina larvae were reared in isolation, at various densities and controlled food levels, and with Bufo melanostictus larvae in laboratory populations. Growth is sigmoid in isolated individuals and mass reaches a maximum just before metamorphosis. In laboratory populations, survival during the larval period was independent of initial population density, but the proportion of the population that successfully completed metamorphosis was a negative exponential function of density. This is interpreted as the result of the slower growth rate in high—density populations arising from the competition for food. The individuals in high—density populations with slower growth rate take a longer time to reach a threshold size and have a lower probability of completing metamorphosis. In higher densities, the threshold size for metamorphosis decreases in comparison to lower density populations.