Data from: Potential mechanisms of coexistence in closely related forbs

The stable coexistence of very similar species has perplexed ecologists for decades and has been central to the development of coexistence theory. According to modern coexistence theory, species can coexist stably (i.e. persist indefinitely with no long-term density trends) as long as species' niche differences exceed competitive ability differences, even if these differences are very small. Recent studies have directly quantified niche and competitive ability differences in experimental communities at small spatial scales, but provide limited information about stable coexistence across spatial scales in heterogeneous natural communities. In this study, we use experimental and observational approaches to explore evidence for niche and competitive ability differences between two closely related, ecologically similar and widely coexisting annual forbs: Trachymene cyanopetala and T. ornata. We experimentally tested for stabilizing niche differences and competitive ability differences between these species by manipulating species' frequencies, under both well-watered and water-stressed conditions. We considered these experimental results in light of extensive field observations to explore evidence of niche segregation at a range of spatial scales. We found little evidence of intra-specific stabilization or competitive ability differences in laboratory experiments while observational studies suggested niche segregation across pollinator assemblages and small-scale microclimate heterogeneity. Though we did not quantify long-term stabilization of coexisting populations of these species, results are consistent with expectations for stable coexistence of similar species via a spatial storage effect allowing niche differences to overcome even small (to absent) competitive ability differences.数十年来，亲缘关系极近的物种如何实现稳定共存始终困扰着生态学家，同时也是共存理论发展的核心议题。根据现代共存理论（modern coexistence theory），只要物种间的生态位差异（niche differences）大于竞争能力差异（competitive ability differences），即便二者差异极小，物种也可实现稳定共存——即种群可无限存续且无长期密度变化趋势。现有研究已在小空间尺度的实验群落中直接量化了生态位与竞争能力差异，但针对异质性自然群落中跨空间尺度的稳定共存现象，相关研究提供的信息仍较为有限。本研究采用实验与观测相结合的方法，探究两种亲缘关系密切、生态特征相似且广泛共存的一年生草本：蓝花松叶芹（Trachymene cyanopetala）与华丽松叶芹（T. ornata）之间的生态位与竞争能力差异证据。本研究通过调控物种接种频率，在充分供水与水分胁迫两种条件下，对这两个物种间的稳定化生态位差异（stabilizing niche differences）与竞争能力差异开展了实验检验。本研究结合大量野外观测数据对上述实验结果进行分析，以探究不同空间尺度下的生态位分化（niche segregation）证据。本研究在室内实验中几乎未发现种内稳定化或竞争能力差异的相关证据，但观测研究显示，两类物种在传粉者类群与小型微生境异质性层面存在生态位分化。尽管本研究未对这两个物种的共存种群开展长期稳定化量化分析，但研究结果与相似物种通过空间存储效应（spatial storage effect）实现稳定共存的理论预期相符：该效应可使生态位差异抵消甚至完全消除竞争能力差异的影响。