Space‐time tradeoffs in the development of precipitation‐based isoscape models for determining migratory origin

Abstract

Precipitation stable isotope patterns over continental scales provide a fundamental tool for tracking origins of migratory species. Hydrogen isotopes from rain and environmental waters are assimilated into animal tissues and may thereby reveal the location where tissues were synthesized. Predictive isotopic maps (or isoscapes) of stable hydrogen isotope values in precipitation (d 2 H p ) are typically generated by time-averaging observations from a global network of stations that have been sampled irregularly in space and time. We previously demonstrated that restricting the temporal range in d 2 H p isoscapes to biologically relevant time frames did not improve predictions of geographic origin for two migratory species in North America and Europe; rather, it decreased the accuracy of assignment. Here, we examined whether the reduction in assignment accuracy stemmed from a decrease in the number of sampling stations available to support isoscape development for shorter time periods. Multiple regression models were used to predict the hydrogen isotope composition in precipitation using isotopic measurements from each station along with a suite of independent variables. The reduction in the number of stations with d 2 H p measurements used to estimate isoscape model parameters did not alter the accuracy and precision of assignments consistently. We also examined accuracy across a range of reduced station numbers and found that mean accuracy was affected only at very low numbers of stations, indicating that the spatial isotopic patterns in precipitation that are useful for assignment applications can be characterized with data from relatively limited data stations. The number and spatial distribution of stations may have more influence when geostatistical models are used to generate isoscapes, as they incorporate spatial correlation in the dataset. The results can be used to guide future research in understanding how data availability and constraints in creating d 2 H p isoscapes may affect predictions of geographic origins.

Matching geographical assignment by stable isotopes with African non-breeding sites of barn swallows Hirundo rustica tracked by geolocation

“…The development of a calibration function explicitly based on feathers of known origin grown within Africa might improve existing δ 2 H isoscapes significantly. However, these fine-tuning possibilities still have to be attended by a general improvement of the resolution and spatial arrangement of the δ 2 Hp-sampling stations (Global Network of Isotopes in Precipitation, GNIP) across the African continent [65]. …”

Regional climate on the breeding grounds predicts variation in the natal origin of monarch butterflies overwintering in Mexico over 38 years

“…While we used a single long-term d 2 H isoscape, we recognize that these may change among years somewhat (Welker, 2012). Nevertheless, we consider the results presented here showing strong climate effects on origins of monarchs to be robust because spatiotemporal variation in isoscape values has a negligible effect of correctly assigning the natal origins of monarchs (Vander Zanden et al, 2015). The probability density of individual i collected in year t having region j as the natal origin is Y it~N (µ jt , ∑ j ) where Y it is a vector of observed d 2 H and d 13 C values, l jt is a vector of the mean predicted d 2 H and year-specific mean predicted d 13 C t values for region j derived from calibrated isoscapes (Supporting information), and Σ j is the positive-definite variance-covariance matrix of d 2 H and d 13 C in region j (Royle & Rubenstein, 2004) based on monarch butterflies raised at known geographic locations .…”

“…While we used a single long‐term δ 2 H isoscape, we recognize that these may change among years somewhat (Welker, ). Nevertheless, we consider the results presented here showing strong climate effects on origins of monarchs to be robust because spatiotemporal variation in isoscape values has a negligible effect of correctly assigning the natal origins of monarchs (Vander Zanden et al ., ).…”

Expanding the Isotopic Toolbox: Applications of Hydrogen and Oxygen Stable Isotope Ratios to Food Web Studies

“…On the contrary, algal and invertebrate δ 2 H values were temporally consistent in a California river system despite changes in environmental conditions known to affect algal δ 13 C values (Finlay et al, 2010). Thus, these patterns may be specific to location, ecosystem type, and species of study, but understanding the time frames over which organisms track changes in environmental δ 2 H water and δ 18 O water values is still in its infancy (Vander Zanden et al, 2014, 2015aTonra et al, 2015).…”