干旱区生态环境知识资源中心

1. Rapid environmental changes are putting many species at risk, particularly niche specialists. In response, species can shift their ranges or remain in place by taking advantage of new resources. The potential for specialists to undergo insitu niche shifts is not well understood yet can buffer species from the effects of long-term environmental change over centuries and millennia.

2. In the Great Basin of western North America, the Chisel-toothed kangaroo rat, Dipodomys microps, is a folivore thought to be an obligate specialist on the desert shrub Atriplex confertifolia. Because of its association with A. confertifolia, D. microps is presumed to have tracked the shrub as it moved south during the last glacial maximum. However, recent phylogeographic evidence indicates that D. microps did not shift or contract its range into a southern refugium.

3. Here we evaluate the role that niche flexibility may have played in allowing this presumed dietary specialist to cope with a changing environment and resource base. We do so using carbon and nitrogen isotopes measured in D. microps bone collagen from modern and fossil specimens spanning the last 8000years at Two Ledges Chamber (TLC) in northwestern Nevada.

4.delta C-13 values indicate that, contrary to expectation, the population of D. microps at TLC consumes a variety of plants other than A. confertifolia, an isotopically distinct C4 shrub, and has done so for millennia. Mixing models suggest that the proportion of C4 in the diet was highest (similar to 35%) in the middle Holocene, and has declined towards the recent, especially over the last 30years. delta N-15 values are consistently elevated through time, suggesting that D.microps at TLC are potentially also consuming a high proportion of insects.

5. Our results indicate that this population of dietary specialists has greater niche flexibility than previously assumed. This implies that, at the species level, even presumed niche specialists may be capable of undergoing niche shifts over centennial to millennial time-scales in response to changing environmental conditions, and highlights the unique role that historical and paleontological data can play in establishing resource-use baselines of the past.