Efficacy of Labeling Wetlands with Enriched 15N to Determine Amphibian Dispersal
Stable isotope enrichment techniques can aid in understanding dispersal of animals. Pond-breeding amphibians often have spatially disjunct populations that depend on immigration for persistence, yet obtaining direct estimates of dispersal rates among wetlands is challenging. We enriched aquatic mesocosms with 15N to “mark” amphibian larvae and determine the feasibility of using enrichment techniques to study dispersal in pond-breeding amphibians. Because newly metamorphosed amphibians in mark-release-recapture studies may not be recaptured until adulthood, we estimated persistence of the 15N enrichment signature up to 3 years post-metamorphosis. We reared larval marbled salamanders (Ambystoma opacum) in artificial mesocosms dosed with 15NH4Cl, and maintained metamorphs on unlabeled prey for 7 months to estimate the biological half life (BHL) of 15N in tissue. Metamorphs in spiked treatments attained δ15N levels >1000 times higher than reference animals (5 ± 1‰), and levels remained ~225 times higher than controls after 7 months. The average 15N BHL was 2.49 ± 0.24 months, indicating that the elevated signature should be discernible for a minimum of 20–28 months after metamorphosis. Our results suggest that 15N enrichment is feasible for field studies of amphibian dispersal, as metamorphs will retain isotope-enriched tissues that persist until at least the second year of breeding.
KeywordsAmbystoma Connectivity Isolated wetland Metapopulation Spiked nitrogen isotopes
We thank Larry Bryan, Stacey Lance, and Jim Beasley for reviews of early drafts of this manuscript, an anonymous reviewer and Robin Warne for additional comments, and Susan Walls and Ken Dodd for insights on age at maturity in southeastern amphibians. Ben Morris and Angie Tucker helped maintain metamorphosed salamanders and weigh samples for isotope analysis, and Heather Brant helped keep the instrumentation up and running. This work was partially supported by the Department of Energy under Award Number DE-FC09-07SR22506 to the University of Georgia Research Foundation.
This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
- Clarkson BR, Schipper LA, Silvester WB (2009) Nutritional niche separation in coexisting bog species demonstrated by 15N-enriched simulated rainfall. Austral Ecol 34:377–385Google Scholar
- Crumpton WG, Goldsborough LG (1998) Nitrogen transformation and fate in prairie wetlands. Great Plains Res 8:57–72Google Scholar
- Dodd CK Jr (2013) Frogs of the United States and Canada. Johns Hopkins University Press, BaltimoreGoogle Scholar
- Hanski I, Gaggiotti OE (2004) Ecology, genetics, and evolution of metapopulations. Alsevier Academic Press, BurlingtonGoogle Scholar
- SAS Institute (2011) SAS system for windows, 93rd edn. SAS Institute, CaryGoogle Scholar
- Jensen J, Camp C, Gibbons W, Elliott M (2008) Amphibians and reptiles of Georgia. University of Georgia Press, AthensGoogle Scholar
- Levins RA (1969) Some demographic and evolutionary consequences of environmental heterogeneity for biological control. Bull Entomol Soc Am 15:237–240Google Scholar
- O’Brien JM, Hamilton SK, Kinsman-Costello LE, Lennon JT, Ostrom NE (2012) Nitrogen transformations in a flow-through wetland revealed using whole-ecosystem pulsed 15N additions. Limnol Oceanogr 57:221–234Google Scholar
- Taylor BE, Scott DE (1997) Effects of larval density dependence on population dynamics of Ambystoma opacum. Herpetol 53:132–145Google Scholar