California has experienced increased drought frequency and intensity in addition to agricultural intensification over the past 120 years. Proxies exist to track these historical changes in environment. However, a lack of tractable study systems has made it challenging to link these changes to the physiology of resident animal populations. In this work, we link historical drought conditions to the physiological ecology and baseline isotopic enrichment of water-stressed grassland habitats through stable isotope analysis of California voles (Microtus californicus) from museum collections spanning 118-years (1891 – 2009). We constructed a sample set (n = 355) of voles collected from coastal and inland habitats of central California, and archived across ten natural history museums.
Results/Conclusions
By associating isotope values of dated hair tissues with monthly statewide drought metrics, we observed a correlation between δ15N and δ18O values and drought intensity. The range in δ15N values (~18‰) is greater than would be expected as a result of dietary shifts across the landscape (~3‰), and is likely attributed to the combined effects of ecophysiological responses of M. californicus to water stress, and isotopic shifts in baseline plant resources with increased drought intensity. Geospatial patterns in δ18O values of hair tissues reflect the isotopic depletion of precipitation from coastal to inland localities. Geospatial patterns in δ34S values of hair tissues reflect baseline isotopic enrichment of coastal habitats. However, comparably enriched δ34S values in the southern-most inland localities appear to reflect sulfur fertilization of croplands and subsequent transfer offsite in dissolved isotopically enriched forms. This study demonstrates that 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.