Geographic assignment with stable isotopes in IsoMAP

Summary Stable isotope ratios of H and O (δ2H and δ18O) are intrinsic properties of biological and geological materials, and can be used to constrain the geographic origin and movements of such materials. One of the most widespread uses of such data in ecology is to reconstruct geographic movements of animals by comparing isotope ratios of chemically inert tissues to predictive models (‘isoscapes’) of spatial isotopic variation in environmental water. Although data analysis for isotope‐based geographic assignment is the subject of ongoing research, a basic framework for this work has emerged. Here, we introduce and document a set of data analysis tools, implemented within the IsoMAP (Isoscapes Modelling, Analysis, and Prediction; http://isomap.org) cyber‐GIS system, that support basic analysis of sample data for geographic assignment applications. We highlight important considerations and potential pitfalls associated with use or misuse of the tools. In addition to increasing the accessibility of geographic assignment analysis, IsoMAP provides several unique capabilities related to the generation of space‐ and time‐specific water isoscapes that may advance the field of isotope‐based assignment. Functionality of the existing toolkit is limited in scope, and although the system will be actively developed in the future, it is intended to complement and not supplant more flexible and customizable analytical tools.