Isotope values of California vole (Microtus californicus) hair relate to historical drought and land use patterns in California, USA

摘要

Increased drought frequency and intensity and agricultural intensification have been key stressors to ecological systems over the past century. Biological proxies (e.g., pollen, tree rings) have been used to track this environmental change; however, linking these changes to the ecology of organisms remains challenging. Here, we link historical drought records to conditions of high water-stress in grassland habitats through the stable isotope analysis of California vole museum specimens (Microtus californicus). Using museum collections spanning 118-years (1891-2009), isotope values of dated hair tissues were associated with statewide drought metrics on the Palmer Drought Severity Index. We observed a positive correlation between delta N-15 and delta O-18 values and drought severity. The range in delta N-15 values (similar to 18 parts per thousand) is greater than what would be expected as a result of dietary shifts across the landscape (similar to 3 parts per thousand), and is likely attributed to the combined effects of physiological responses of M. californicus and isotopic shifts in plant resources with increased water-stress. Geospatial patterns in delta S-34 values of hair tissues reflect higher baseline isotope values in coastal habitats. However, comparably high delta S-34 values in the southern-most inland localities suggest sulfur fertilization of croplands and subsequent transfer to surrounding grassland habitats in S-34 enriched forms. A broad delta C-13 range (- 28.7 to - 14.3 parts per thousand) further suggests the consumption of C-3 and C-4 plant-based dietary proteins. As shown here, stable isotope analysis of museum collections can provide a climate and land use record based on the physiological performance and ecology of a study species in a region affected intensely by anthropogenic activities.