Efficacy of Labeling Wetlands with Enriched 15N to Determine Amphibian Dispersal

Abstract

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.