Species range sizes and realized niche breadths vary tremendously. Understanding the source of this variation has been a long-term aim in evolutionary ecology and is a major tool in efforts to ameliorate the impacts of changing climates on species distributions. Species ranges that span a large climatic envelope can be achieved by a collection of specialized genotypes locally adapted to a small range of conditions, by genotypes with stable fitness across variable environments, or a combination of these factors. We asked whether fitness expressed along a key niche axis, water availability, could explain a species' realized niche breadth, its geographic range and climate breadth, in 11 species from a clade of jewelflowers whose range sizes vary by two orders of magnitude. Specifically, we explored whether the range size of a species was related to the ability of genotypes (maternal families) to maintain fitness across a range of experimental water availabilities based on 30-year historical field precipitation regimes. We operationally characterized fitness homeostasis through the coefficient of variation in fitness of a genotype (family) across the experimental water gradient. We found that species with genotypes that had high fitness homeostasis, low variation in fitness over our treatments, had larger climatic niche breadth and geographic range in their field distributions. The result was robust to alternate measures of fitness homeostasis. Our results show that the fitness homeostasis of genotypes can be a major factor contributing to niche breadth and range size in this clade. Fitness homeostasis can buffer species from loss of genetic diversity and under changing climates, provides time for adaptation to future conditions.

中文翻译：

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跨实验水梯度的健身稳态预测物种的地理范围和气候广度

物种范围大小和实现的生态位宽度差异很大。了解这种变异的来源一直是进化生态学的长期目标，也是努力改善气候变化对物种分布影响的主要工具。跨越大气候范围的物种范围可以通过局部适应小范围条件的专门基因型的集合，通过在可变环境中具有稳定适应性的基因型，或这些因素的组合来实现。我们询问沿关键生态位轴表达的适合度，水的可用性，是否可以解释一个物种实现的生态位宽度，其地理范围和气候宽度，在 11 个物种中，这些物种来自 jewelflowers 的一个分支，其范围大小相差两个数量级。具体来说，我们探讨了一个物种的范围大小是否与基因型（母系）在基于 30 年历史田间降水状况的一系列实验水可用性范围内保持适应性的能力相关。我们通过跨实验水梯度的基因型（家族）的适应性变异系数，在操作上表征适应性稳态。我们发现，基因型的物种具有高适应性稳态、在我们的治疗过程中适应性变化小、在其田间分布中具有更大的气候生态位广度和地理范围。结果对于健身稳态的替代措施是稳健的。我们的结果表明，基因型的适应度稳态可能是影响该进化枝生态位宽度和范围大小的主要因素。