Data from: Overall seed dispersal effectiveness is lower in endemic Trillium species than in their widespread congeners

PREMISE OF THE STUDY: Comparing ecological attributes of endemic species with related, widespread species can reveal differences accounting for rarity. Forests of the southeastern US are home to many range-restricted endemic and widespread species of Trillium, a genus of ant-dispersed herbs. Evidence suggests that aspects of seed-related life history stages are often correlated with plant rarity, but few studies have tested whether the process of seed dispersal differs for endemic and widespread species. To address this question, we compare aspects of seed dispersal effectiveness (SDE) for three sympatric widespread-endemic Trillium species pairs. METHODS: We observed ant seed dispersal for Trillium species pairs at eight sites, recorded numbers of seeds dispersed and dispersal distances, and described disperser interactions. To test disperser preference, we presented seeds of each pair to captive colonies of Aphaenogaster picea, a keystone disperser. Seeds were assigned scores based on worker behavior, and we recorded proportions of seeds dispersed after 60 minutes and 24 hours. KEY RESULTS: Field observations yielded some significant within-pair differences. Ants dispersed more seeds of widespread species for all pairs, although dispersal distances did not differ. In laboratory experiments, after 24 hours, ants dispersed more seeds of widespread species into nests. CONCLUSIONS: Endemic Trillium species exhibited lower overall SDE than their widespread congeners. These findings add to the list of ecological and demographic challenges that face endemic plants when compared to common congeners. Lower SDE may negatively impact reproductive rates and the colonization of new habitats, which may contribute to patterns of endemism. If you would like your personal information to be removed from the database, please contact the publication office.

研究背景（PREMISE OF THE STUDY）：将特有物种与其近缘广布物种的生态属性进行比较，可揭示导致物种稀有性的差异成因。美国东南部的森林中栖息着多种分布范围受限的特有种与广布种延龄草属（Trillium）植物，该类群均为蚁播草本植物。已有研究表明，与种子相关的生活史阶段特征通常与植物稀有性存在关联，但鲜有研究检验特有种与广布种的种子扩散过程是否存在差异。为解答这一科学问题，本研究对3组同域分布的广布-特有延龄草物种对的种子扩散有效性（seed dispersal effectiveness，SDE）相关特征展开对比分析。
研究方法（METHODS）：我们在8个样地对延龄草物种对的蚁播过程进行了观测，记录了扩散种子数量与扩散距离，并描述了扩散者的互作模式。为检验扩散者的偏好性，我们将各物种对的种子提供给作为关键扩散者的褐黑铺道蚁（Aphaenogaster picea）的人工饲养种群。实验中根据工蚁行为对种子进行评分，并记录了60分钟与24小时后被扩散的种子比例。
主要结果（KEY RESULTS）：野外观测结果显示，部分物种对内存在显著差异。所有物种对中，蚂蚁扩散的广布种种子数量均更多，但扩散距离并未出现显著差异。室内实验结果表明，24小时后蚂蚁将更多广布种的种子搬运至蚁巢内部。
研究结论（CONCLUSIONS）：特有延龄草物种的整体种子扩散有效性显著低于其近缘广布同属物种。本研究结果进一步补充了特有植物相较于广布共源种所面临的生态与种群统计学挑战。较低的种子扩散有效性可能会对繁殖率以及新栖息地的定居能力产生负面影响，这或许是促成特有分布格局的关键因素之一。
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