Using Stable Isotopes as a
Tool
for Marking Amphibians
David Scott, Betsie Rothermel, Melissa Pilgrim, and Chris Romanek
 |
Stable isotopes such as 15N and 13C have a variety of uses in ecological studies, yet few amphibian studies have utilized stable isotope techniques. We plan to sample 15N and 13C levels in pond-breeding amphibians, as well as artificially elevate the ratios of these isotopes (relative to the more common isotopes 14N and 12C) in experimental populations of aquatic amphibian larvae. These studies will enable a better understanding of the trophic structure of amphibian communities, and will possibly lead to a new tool for use in studies of amphibian dispersal and metapopulation dynamics. |
| To collect animals for standard stable isotope analysis of amphibians from natural wetlands we will use routine trapping techniques such as minnow traps, dip nets, and drift fence/pitfall trap arrays. In conjunction with samples to determine normal isotopic ratios in a variety of species we will rear populations of larvae of select species in experimental tanks (i.e., 1,000-L artificial ponds created using known techniques to establish a natural pond that includes organic material, bacterial communities, periphyton and other algal communities, and a wide assortment of zooplankton and aquatic insects). Once artificial pond set-up is completed (i.e., which means that robust algal and zooplankton populations are established in the tanks), some artificial ponds will receive 15N and 13C enhancement at concentrations up to 0.3 ppm. We will also add frog, toad, and salamander larvae (at realistic densities that have been observed in the field) to appropriate treatments. Amphibian larvae will be sequentially sub-sampled at 3-10 day intervals to determine isotope uptake, retention, and elimination rates. Surviving larvae that develop and metamorphose will be held in natural terrestrial enclosures for 1-3 months. These animals will be supplementally fed with crickets and worms, and 2-3 individuals will be euthanized weekly to determine isotope elimination rates. Survivors at the end of three months will be toe-clipped to create a permanent mark as well as provide tissue for isotope analysis. |