Data from: Small-mammal isotope ecology tracks climate and vegetation gradients across western North America

Stable carbon, nitrogen, hydrogen and oxygen isotopes have been used to infer aspects of species ecology and environment in both modern ecosystems and the fossil record. Compared to large mammals, stable isotopic studies of small-mammal ecology are limited; however, high species and ecological diversity within small mammals presents several advantages for quantifying resource use and organism–environment interactions using stable isotopes over various spatial and temporal scales. We analyzed the isotopic composition of hair from two heteromyid rodent species, Dipodomys ordii and Perognathus parvus, from localities across western North America in order to characterize dietary variation in relation to vegetation and climatic gradients. Significant correlations between the carbon isotopic composition (δ13C) of these species and several climatic variables imply that seasonal temperature and precipitation control the composition and distribution of dietary resources (grass seeds). Our results also suggest a moisture influence on the nitrogen isotopic composition (δ15N) of heteromyid diets. Population- and species-level variation in δ13C and δ15N values record fine-scale habitat heterogeneity and significant differences in resource use between species. Using classification and regression-tree techniques, we modeled the geographic variation in heteromyid δ13Cdiet values based on 10 climatic variables and generated an isotope landscape model (‘isoscape’). The isoscape predictions for δ13Cdiet differ from expectations based on observed C4 distributions and instead indicate that D. ordii and P. parvus record seasonally abundant grass resources, with additional model deviations potentially attributed to geographic variation in dietary selection. The oxygen and hydrogen isotopic composition of D. ordii is enriched relative to local meteoric water and suggests that individuals rely on highly evaporated water sources, such as seed moisture. Based on the climatic influences on vegetation and diet documented in this study, the isotopic composition of small mammals has high potential for recording ecological responses to environmental changes over short and long time scales.稳定碳、氮、氢、氧同位素已被用于推断现代生态系统与化石记录中物种生态学特征及环境信息。相较于大型哺乳动物，小型哺乳动物生态学的稳定同位素研究相对匮乏；但小型哺乳动物拥有极高的物种与生态多样性，使其在不同时空尺度下利用稳定同位素量化资源利用方式与生物-环境交互作用时具备多重优势。本研究对北美西部多个采样点的两种异鼠科啮齿动物——奥氏更格卢鼠（Dipodomys ordii）和小更格卢鼠（Perognathus parvus）的毛发同位素组成进行分析，以解析其饮食变异与植被及气候梯度的关联。两种鼠类的碳同位素组成（δ¹³C）与多项气候变量间存在显著相关性，表明季节温度与降水调控了其饮食资源（禾本科植物种子）的组成与分布格局。本研究结果同时显示，湿度对异鼠科动物饮食的氮同位素组成（δ¹⁵N）存在影响。δ¹³C与δ¹⁵N值在种群与物种水平上的变异，反映了精细尺度的生境异质性，以及不同物种间资源利用方式的显著差异。本研究采用分类与回归树技术，基于10项气候变量对异鼠科动物的饮食δ¹³C值的地理变异进行建模，构建了同位素景观模型（isoscape）。该同位素景观模型对饮食δ¹³C值的预测结果与基于已观测到的C4植物分布的预期不符，反而表明奥氏更格卢鼠与小更格卢鼠记录了季节性富集的禾本科植物资源，模型的额外偏差可能源于不同区域间饮食选择的差异。奥氏更格卢鼠的氧与氢同位素组成相较于当地大气降水更为富集，表明其个体依赖经强烈蒸发作用的水源（如种子所含水分）。基于本研究揭示的气候对植被与饮食的调控作用，小型哺乳动物的同位素组成具备极高潜力，可用于记录不同时间尺度下生物对环境变化的生态响应。