Small mammal utilization of pulsed resources quantified through stable isotope analysis

In this study we examine rain-driven pulses of production in C₃ and C₄ plant functional groups and use stable isotope analysis to quantify how these pulses influence nutrient flux from plants to rodents and rodent population dynamics. Our site is located at the Sevilleta NWR/LTER, in the Chihuahuan Desert of New Mexico, where C₃ plants increase production in response to winter rains and C₄ plants respond to summer monsoons. From 2005 to 2006, New Mexico experienced a shift from high winter and low summer precipitation to low winter and high summer precipitation, changing the seasonal plant composition. C₃ and C₄ plants differ in δ¹³C isotopic composition because of different photosynthetic pathways and δ¹⁵N increases 3.3‰ per trophic level. We collected blood plasma monthly, which indicates an animal’s diet during the previous 5-7 days, and analyzed the plasma for δ¹³C and δ¹⁵N. These values were compared to the δ¹³C and δ¹⁵N of vegetation and arthropods to quantify their proportions in rodent diets. From April to November 2005, plasma δ¹³C enriched for some rodents, indicating a shift from C₃ to C₄ plant utilization. In 2006, when C₃ plant production decreased, all species increased diet variablility and reliance on C₄ plants.  Enrichment patterns reflected diet and habitat specialization and δ¹⁵N values further revealed resource driven trophic dynamics within this food web. Further results may show how changes in abundance and availability of plant functional groups, that occur with climate change, not only affect rodent diet, but possibly survival, population size and species diversity.