Data from: Isotopic niche variation from the Holocene to today reveals minimal partitioning and individualistic dynamics among four sympatric desert mice

1.Species interact with each other and their environment over a range of temporal scales, yet our understanding of resource partitioning and the mechanisms of species coexistence is largely restricted to modern time-scales of years to decades. Furthermore, the relative magnitudes of inter- versus intraspecific variation in resource use are rarely considered, despite the potential for the latter to influence a species’ ability to cope with changing environmental conditions.

2.Modern desert rodent communities are thought to be strongly structured by competitive interactions, with niche partitioning of food resources hypothesized to explain the coexistence of multiple sympatric granivores. Yet the stability of niche dynamics over extended temporal scales within desert rodent communities is unknown.

3.I examined the isotopic niche dynamics of four common sympatric desert mice (three granivores: Chaetodipus formosus, Perognathus longimembris, and Reithrodontomys megalotis, and one omnivore: Peromyscus maniculatus) in the Smoke Creek Desert of northwestern Nevada using 13C and 15N isotopes obtained from “Modern” (2008-2013 CE), “Historical” (1989-2005 CE), and Holocene fossil specimens spanning the last ca. 7,500 years.

4.I found significant variation in niche position, niche breadth, and interspecific niche overlap of these species through time. The niche breadth dynamics of the cricetids (P. maniculatus and R. megalotis) were positively correlated with one another, while the niche breadth dynamics of the heteromyid C. formosus were negatively correlated with those of all other species. Body size, dietary functional group, paleoenvironmental trends, and time-averaging provided little explanatory power. Importantly, Modern and Historical patterns of resource use and partitioning differed from Holocene baselines in terms of decreased niche overlap and in the absolute and relative position of each species’ niche in at least one isotopic axis.

5.These observations suggest that each species’ resource use changed individualistically over the Holocene, hence niche dynamics are poorly explained by the hypothesis of temporally-stable species interactions at millennial time-scales. Furthermore, changes to the resource base over the last century (likely due to the spread of invasive cheatgrass) may be increasing resource partitioning in the Modern, pushing species past their baseline ranges of resource use variation.

1. 物种会在一系列时间尺度上彼此互动，并与环境发生相互作用，但当前学界对资源划分以及物种共存机制的认知，大多局限于数年至数十年的现代时间尺度。此外，尽管种内变异可能影响物种应对环境变化的能力，但资源利用过程中的种间与种内变异的相对幅度却极少被纳入考量。
2. 学界普遍认为现代沙漠啮齿动物群落的结构深受种间竞争相互作用的塑造，且食物资源的生态位划分被假说为多种同域食籽动物得以共存的原因。然而，沙漠啮齿动物群落在长时间尺度下的生态位动态稳定性仍属未知。
3. 本研究以美国内华达州西北部斯莫克溪沙漠（Smoke Creek Desert）为研究区域，利用取自‘现代’（公元2008-2013年）、‘历史’（公元1989-2005年）以及距今约7500年的全新世（Holocene）化石标本的碳13（¹³C）与氮15（¹⁵N）同位素数据，分析了4种常见同域分布荒漠小鼠的同位素生态位动态：其中3种为食籽动物——Chaetodipus formosus、Perognathus longimembris和Reithrodontomys megalotis，另1种为杂食动物Peromyscus maniculatus。
4. 本研究发现，随着时间推移，这些物种的生态位位置、生态位宽度以及种间生态位重叠均存在显著变化。仓鼠科（cricetids）物种（P. maniculatus与R. megalotis）的生态位宽度动态呈显著正相关，而异鼠科（heteromyid）物种C. formosus的生态位宽度动态则与其余所有物种呈负相关。体型大小、食性功能群、古环境趋势以及时间平均效应对上述结果的解释力均较弱。值得注意的是，现代与历史时期的资源利用及划分模式与全新世基线存在显著差异：具体表现为种间生态位重叠降低，且至少在一条同位素轴上，各物种生态位的绝对与相对位置均发生了改变。
5. 上述结果表明，全新世以来各物种的资源利用模式均呈现出个体独特的变化轨迹，因此，千年尺度下物种相互作用具有时间稳定性这一假说，无法很好地解释生态位动态。此外，近一个世纪以来资源基础的变化（大概率由入侵性雀麦草的扩散所导致）可能提升了现代群落中的资源划分程度，推动各物种的资源利用变异超出了其基线范围。