Cohort patterns in Rana tadpole metamorphosis

This study explores the cohort patterns in a size versus time plot of individual metamorphs of Rana tadpoles. This meta-study was based on a number of studies where any of three species of Rana tadpoles were raised in tanks under various treatments (variation in source pond, tadpole density, drying regime, hatching date, food level and competitors). A frequent pattern was found where there was an initial decrease in metamorph size as more slowly developing tadpoles metamorphosed. This negative trend sometimes changed to positive as later metamorphs appeared. The later metamorphs were often as large, or even larger, than those first to metamorphose, giving the plot a U-shaped pattern. Also, a number of field studies of two of the Rana species’ were analysed for the same aspect. The U-shaped pattern was much rarer but it did occur. A positive linear slope, rather than a negative one, was also found occasionally. A large number of factors affect the growth and development rates in tadpoles, adaptively and non-adaptively, and thus determine their size at the time of metamorphosis. How these can contribute to the found metamorphosis patterns is discussed