Ecologists have traditionally studied intraspecific variation by sampling species across their geographic ranges. However, whether this classic approach produces samples that accurately represent species' climatic niches is largely unknown. Alternative niche-based study designs using species' climatic niches to inform sampling locations should more efficiently and completely capture the breadth of the niche, but the magnitude of this difference and how it may vary is unclear. Here we use conifers as a model system to explore these issues and reach specific recommendations for future sampling designs. Using an independent data set of high-quality species' occurrences, we first show that recent publications examining variation across geographic space do a poor job of capturing the full breadth of species' niches, such that on average, only 22% of species' niche space was sampled. This was also true of a large compiled database, the International Tree-Ring Data Bank (ITRDB), which yielded average niche coverage of only 45%. Finally, we simulated common sampling designs (i.e. random points, grids and transects) in both geographic and niche-based sampling frameworks. Using two sampling metrics, niche coverage and niche undersampling, we measured how completely and evenly these simulated studies characterized the niches of 64 North American conifers. Niche-based sampling better represented species' niches than geographic sampling, with the magnitude of this difference depending on study design and sample size. Niche-based gridded study designs achieved the most complete sampling at all but the smallest sample sizes, covering ~15–25% more of a species' niche than similar designs implemented geographically. With fewer than 10 samples, however, all study designs performed poorly, and niche-based transects achieved slightly higher niche coverage. Consequently, when more than a handful of samples are collected, we recommend that studies seeking to characterize variation across a species' niche consider using a gridded study design implemented in a niche-based sampling framework.

中文翻译：

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评估替代研究设计以优化物种气候生态位采样

生态学家传统上通过在其地理范围内对物种进行采样来研究种内变异。然而，这种经典方法是否产生准确代表物种气候生态位的样本在很大程度上是未知的。使用物种的气候生态位来通知采样位置的基于生态位的替代研究设计应该更有效和更完整地捕捉生态位的广度，但这种差异的大小及其可能如何变化尚不清楚。在这里，我们使用针叶树作为模型系统来探索这些问题并为未来的抽样设计提出具体建议。使用高质量物种出现的独立数据集，我们首先表明，最近发表的研究跨地理空间变化的出版物在捕捉物种生态位的全部范围方面做得很差，例如，平均而言，与地理上实施的类似设计相比。然而，在少于 10 个样本的情况下，所有研究设计都表现不佳，基于生态位的横断面实现了略高的生态位覆盖率。因此，当收集的样本超过少数时，我们建议寻求表征物种生态位变异的研究考虑使用在基于生态位的抽样框架中实施的网格研究设计。