POPULATION REGULATION IN THE WOOD FROG, RANA-SYLVATICA, FROM 3 DIVERSE GEOGRAPHIC LOCALITIES

This study summarizes demographic data on the wood frog, Rana sylvatica, from Maryland (two populations over 7 years), Virginia (seven populations over 8 years), and Michigan (one population over 13 years). Within each geographic locality breeding adult population size was rarely stable and all populations passed through major bottlenecks. Reproductive failures (no larvae metamorphosed) were not uncommon, nor were reproductive bonanzas, where juvenile production exceeded the replacement rate by up to a factor of 6. A key-factor analysis showed that larval mortality in all localities, accounted for the year to year fluctuations in adult population size. However, the phase of the life cycle in which regulation occurred varied among localities. Larval mortality was strongly density-dependent in Maryland, but only weakly so in Virginia, and not in Michigan. In Virginia and Michigan adult mortality was density-dependent, Fecundity was density-dependent in all three localities. Density-independent factors also influenced population size: large fluctuations in adult population size primarily occurred due to drought-induced catastrophic larval mortality and bacterial epidemics that dramatically affected larval survival in Virginia. Adult mortality, but not juvenile mortality, was also negatively related to precipitation levels in all localities.