Data from: Historical and recent processes shaping the geographic range of a rocky intertidal gastropod: phylogeography, ecology, and habitat availability

Factors shaping the geographic range of a species can be identified when phylogeographic patterns are combined with data on contemporary and historical geographic distribution, range-wide abundance, habitat/food availability, and through comparisons with codistributed taxa. Here, we evaluate range dynamism and phylogeography of the rocky intertidal gastropod Mexacanthina lugubris lugubris across its geographic range – the Pacific coast of the Baja peninsula and southern California. We sequenced mitochondrial DNA (CO1) from ten populations and compliment these data with museum records, habitat availability and range-wide field surveys of the distribution and abundance of M. l. lugubris and its primary prey (the barnacle Chthamalus fissus). The geographic range of M. l. lugubris can be characterized by three different events in its history: an old sundering in the mid-peninsular region of Baja (~ 417,000 years ago) and more recent northern range expansion and southern range contraction. The mid-peninsular break is shared with many terrestrial and marine species, although M. l. lugubris represents the first mollusc to show it. This common break is often attributed to a hypothesized ancient seaway bisecting the peninsula, but for M. l. lugubris it may result from large habitat gaps in the southern clade. Northern clade populations, particularly near the historical northern limit (prior to the 1970s), have high local abundances and reside in a region with plentiful food and habitat – which makes its northern range conducive to expansion. The observed southern range contraction may result from the opposite scenario, with little food or habitat nearby. Our study highlights the importance of taking an integrative approach to understanding the processes that shape the geographic range of a species via combining range-wide phylogeography data with temporal geographic distributions and spatial patterns of habitat/food availability.

当将系统发生生物地理学（phylogeography）模式与物种的当代及历史地理分布、全分布区种群丰度、栖息地/食物可获得性数据相结合，并与同分布类群开展对比时，便可明确塑造物种地理分布范围的核心影响因素。本研究针对潮间带岩栖腹足类*Mexacanthina lugubris lugubris*的全分布区——下加利福尼亚半岛太平洋沿岸与加利福尼亚南部——的分布动态与系统发生生物地理学特征展开评估。我们对10个种群的线粒体DNA（CO1基因）进行了测序，并辅以馆藏标本记录、栖息地可获得性数据，以及针对*M. l. lugubris*及其主要猎物纹藤壶（*Chthamalus fissus*）的全分布区分布与丰度野外调查数据。*M. l. lugubris*的地理分布范围可通过其演化历史中的三类事件加以表征：下加利福尼亚半岛中部区域的古老分化事件（约41.7万年前），以及较近期的北部分布区扩张与南部分布区收缩事件。这一半岛中部的分化断点与诸多陆生及海洋类群所共有的分化模式一致，而*M. l. lugubris*则是首个展现该模式的软体动物。这类常见的分化断点通常被归因于假说中曾将半岛一分为二的古海道，但对于*M. l. lugubris*而言，该断点可能源于南部支系存在大面积的栖息地缺失。北部支系的种群，尤其是处于历史北界（1970年代之前）附近的种群，当地种群丰度较高，且栖息区域食物与栖息地资源充裕——这使得其北部分布区具备扩张的有利条件。观测到的南部分布区收缩则可能源于相反的情形：周边食物与栖息地资源匮乏。本研究强调了整合研究方法的重要性：通过结合全分布区系统发生生物地理学数据、时序地理分布数据，以及栖息地/食物可获得性的空间分布模式，来解析塑造物种地理分布范围的核心过程。