Am Nat. 2019 Jun;193(6):786-797. doi: 10.1086/703187. Epub 2019 Apr 23.
Species' geographic distributions have already shifted during the Anthropocene. However, we often do not know what aspects of the environment drive range dynamics, much less which traits mediate organisms' responses to these environmental gradients. Most studies focus on possible climatic limits to species' distributions and have ignored the role of biotic interactions, despite theoretical support for their importance in setting distributional limits. We used field experiments and simulations to estimate contributions of mammalian herbivory to a range boundary in the Californian annual plant ssp. . A steep gradient of increasing probability of herbivory occurred across the boundary, and a reanalysis of prior transplant experiments revealed that herbivory drove severalfold declines in lifetime fitness at and beyond the boundary. Simulations showed that populations could potentially persist beyond the range margin in the absence of herbivory. Using data from a narrowly sympatric subspecies, , we also showed that delayed phenology is strongly associated with ssp. 's susceptibility to herbivory and low fitness beyond its border. Overall, our results provide some of the most comprehensive evidence to date of how the interplay of demography, traits, and spatial gradients in species interactions can produce a geographic range limit, and they lend empirical support to recent developments in range limits theory.
在人类世，物种的地理分布已经发生了变化。然而，我们通常不知道是什么环境因素驱动着范围动态，更不知道哪些特征介导了生物体对这些环境梯度的反应。尽管理论上支持生物相互作用在确定分布极限方面的重要性，但大多数研究都集中在可能的气候限制对物种分布的影响上，而忽略了它们的作用。我们使用野外实验和模拟来估计哺乳动物食草作用对加利福尼亚一年生植物亚种的分布范围边界的贡献。在边界上发生了食草概率逐渐增加的陡峭梯度，对先前移植实验的重新分析表明，食草作用导致在边界内和边界外的终生适应性降低了几倍。模拟表明，如果没有食草作用，种群有可能在分布范围的边缘之外生存。我们还利用与近缘亚种的数据，表明延迟物候与亚种对食草作用的敏感性和边界外低适应性密切相关。总的来说，我们的结果提供了迄今为止最全面的证据之一，说明了种群动态、特征和物种相互作用的空间梯度如何相互作用产生地理范围限制，并为最近的范围限制理论的发展提供了经验支持。
