PS 6-60
Long-term monitoring of salamander energy subsidies in the Southeast suggests aquatic flux is more common than terrestrial flux and highly dependent on hydroperiod for five salamander species
Very little research has placed amphibian species within the context of nutrient dynamics and ecosystem productivity. The few studies to investigate amphibians suggest they have important consequences to nutrient and energy dynamics into and out of wetland environments. However, many of these studies have been of very short duration (< 3 yrs). In this experiment we analyzed data from a long-term data set (> 35 years) to understand whether 5 salamander species (Ambystoma opacum, A. talpoideum, A. tigrinum, Notophthalmus viridescens, Eurycea quadridigitata) were providing a net nutrient flux into (aquatic) or out of (terrestrial) ephemeral wetland communities. We take data from a long-term data set in which an ephemeral wetland (Rainbow Bay on the Savannah River Site) was surrounded by a drift fence and monitored daily since September 1978. Using counts of individuals and weight/length or weight/egg regressions, we estimated dry biomass (g) into and out of the wetland each year. We were also able to consider mortality of adults within the wetland during breeding, which has previously not been considered in salamander energy subsidy research. We then asked the question to what extent hydroperiod is related to the direction of flux and if this relationship differs among species.
Results/Conclusions
Over the 35 years of observation, aquatic subsidies were far more common for all 5 species than terrestrial flux. Including adult mortality in the wetland during breeding migrations significantly affected flux estimates, but did not significantly affect the direction of the flux (aquatic/terrestrial). Probability of terrestrial flux greatly increased with increased hydroperiod for all species. A. talpoideum, A. tigrinum, and N. viridescens had very similar logistic relationships between hydroperiod and terrestrial flux. A. opacum has greater probability of terrestrial flux at shorter hydroperiods where the other salamanders are unable to develop rapidly enough to recruit juveniles. E. quadridigitata had the most unusual pattern that appeared to be a linear increase in terrestrial flux probability over the hydroperiods observed in the 34 year study. Perhaps with greater hydroperiods, the logistic relationship between hydroperiod and terrestrial flux would be resolved for E. quadridigitata. Our results suggest that great terrestrial flux from wetland environments for salamander species may be rare and limited to years of long hydroperiod providing opportunity for high productivity. Future research will create a model to understand the importance of the salamander terrestrial energy flux in relation to C/N/P cycling in the terrestrial ecosystem.