Eco-evolutionary causes and consequences of rarity in plants: a meta-analysis

Species differ dramatically in their prevalence in the natural world, with
many species characterized as rare due to restricted geographic
distribution, low local abundance, and/or habitat specialization. We
investigated eco-evolutionary causes and consequences of rarity with
phylogenetically-controlled meta-analyses of population genetic diversity,
fitness, and functional traits in rare and common congeneric plant
species. Our syntheses included 252 rare species and 267 common congeners
reported in 153 peer-reviewed articles published from 1978-2020 and one
manuscript in press. Rare species have reduced population genetic
diversity, depressed fitness, and smaller reproductive structures than
common congeners. Rare species also could suffer from inbreeding
depression and reduced fertilization efficiency. By limiting their
capacity to adapt and migrate, these characteristics could influence
contemporary patterns of rarity and increase the susceptibility of rare
species to rapid environmental change. We recommend that future studies
present more nuanced data on the extent of rarity in focal species, expose
rare and common species to ecologically-relevant treatments, including
reciprocal transplants, and conduct quantitative genetic and population
genomic analyses across a greater array of systems. This research could
elucidate the processes that contribute to rarity and generate robust
predictions of extinction risks under global change.

自然界中不同物种的种群丰度差异悬殊，诸多物种因地理分布受限、本地种群密度偏低，或是生境特化而被归类为稀有物种。
本研究针对稀有与近缘同属常见植物物种的种群遗传多样性、适合度及功能性状开展系统发育控制下的元分析，以此探究物种稀有性的生态与进化成因及后果。
本研究的综合分析纳入了1978年至2020年间发表的153篇同行评议论文，以及1篇待刊稿件中记载的252个稀有物种与267个近缘同属常见物种。
相较于近缘同属常见物种，稀有物种的种群遗传多样性更低、适合度更差，且生殖结构尺寸更小。
此外，稀有物种还可能面临近交衰退以及受精效率下降的问题。
这些特征会限制物种的适应与迁移能力，进而影响当前的稀有性格局，并提升稀有物种对快速环境变化的敏感性。
我们建议未来研究应提供更为精细的目标物种稀有性程度数据，让稀有与常见物种接受符合生态学意义的处理（包括互惠移栽实验），并在更多样的生态系统中开展定量遗传与种群基因组学分析。
此类研究可阐明驱动物种稀有性的核心过程，并为全球变化背景下的物种灭绝风险提供可靠的预测依据。