PS 6-61
Understanding effects of leaf litter in the terrestrial environment on growth and survival of post-metamorphic wood frogs

Monday, August 10, 2015
Exhibit Hall, Baltimore Convention Center
Hilary B. Rollins, Biology, Case Western Reserve University, Cleveland, OH
Michael F. Benard, Department of Biology, Case Western Reserve University, Cleveland, OH

In amphibian ecology, many studies have investigated how environmental factors affect survival and growth during the aquatic larval stage. Relatively few studies have investigated how environmental factors in the terrestrial stage affect post-metamorphic growth and survival.  One factor which may affect amphibians in the terrestrial environment is leaf litter. In northeastern United States beech-maple communities, leaf litter generates strata for invertebrates, provides nutrients and creates shelter for post-metamorphic amphibians. We set out to answer three questions about post-metamorphic amphibian ecology and how it is affected by leaf litter. First, does compensatory growth occur in amphibians that start at different sizes at metamorphosis? Second, does leaf litter input increase growth and survival of amphibians? Third, is there a relationship between frog traits and leaf litter decomposition? We raised wood frog (Rana sylvatica) larvae to small metamorphic size in mesocosms without supplemental food and to large metamorphic size in mesocosms with supplemental food. Four frogs from the same size treatment were placed in terrestrial enclosures with a natural amount of leaf litter or a doubled amount of leaf litter from the surrounding forest floor. In addition, we used leaf packs to assess treatment effects on decomposition and nutrient cycling processes.


Neither leaf litter treatments nor frog size treatments nor their interaction had significant effects on the number of frogs recovered from each enclosure or on the percent growth of frogs.  We did find a significant positive effect of initial size at metamorphosis on final frog mass (i.e., frogs that were larger at metamorphosis were larger at the end of the experiment). The fact that size at metamorphosis did not affect percent growth is particularly interesting because it indicates a lack of compensatory growth.  In other words, frogs which received no supplemental food in the aquatic environment and metamorphosed at a smaller size were not able to catch up to those individuals who metamorphosed at a larger size.  In contrast to our results, compensatory growth has been demonstrated in other closely related amphibians. We also found no effect of our treatments on leaf decomposition. However, we did find a significant negative relationship between the number of frogs surviving to the end of the experiment and the rate of leaf decomposition. This result suggests an indirect relationship of frog density on the invertebrate community in the leaf litter.