The Spatial Distribution of Terrestrial Stable Carbon Isotopes in North America, and the Impacts of Spatial and Temporal Resolution on Static Ecological Models

Due to the unique spatial and temporal characteristics of ecological phenomena, the extent and grain size of spatial data sets essentially filter the observations. This thesis examines the impacts of temporal and spatial resolution on the modeling of terrestrial stable carbon isotopic landscapes (isoscapes). I model the distribution of leaf stable carbon isotope composition (delta13C) for the continent of North America at multiple temporal and spatial resolutions. I generate each delta13C isoscape variation by first predicting the relative abundance of C3/C4 vegetation cover using monthly climate grids, crop distribution/type grids, and remote sensing data of plant life form, and then applying the respective leaf delta13C endmembers to each pixel. One application of isoscapes is predicting the geographic origin of migratory animals by relating the isotopic signature of animal tissue to environmental isotope values. I conduct multiple exercises in geographic origin assignment using known-origin feather isotope data of mountain plover (Charadrius montanus) chicks as an indirect means of testing the impact of resolution on delta13C isoscapes. Results indicate that temporal resolution does have a significant impact on predicted isoscape layers, and in turn, geographic origin assignment efficacy. Temporal periods that did not correspond to tissue growth exhibited a mismatch in the range of predicted vegetation delta13C values relative to the range of measured feather delta13C values and therefore were not useful in generating geographic origin assignments. The spatial resolution of modeled delta13C minimally impacted assignment accuracy and precision compared to temporal resolution; however, the current analysis was limited by the spatial resolution of the input data set. These results should be further explored to better characterize spatiotemporal ecological characteristics of migratory animals and to improve modeling of the isotopic landscape itself