Cirsium pitcheri is a federally threatened, monocarpic perennial thistle species endemic to the Great Lakes region of the United States and Canada. Human habitat disturbances, lake level fluctuations and climate change have resulted in extensive declines of C. pitcheri populations. Seed predation by non-native weevil, Larinus planus, has also further exacerbated C. pitcheri population declines and reduced its projected time to extinction to less than 20 years. Given the widespread presence of L. planus throughout C. pitcheri’s range, studies that investigate its impacts are essential for understanding and predicting changes in the life histories and demographic rates of C. pitcheri populations. We present a two-year field study and common garden experiment that examine the relationship between C. pitcheri whole plant fecundity and capitulum position and assess the impacts of L. planus on C. pitcheri seed production. This study is part of an on-going population viability analysis and aims to inform C. pitcheri conservation and restoration efforts. Our results demonstrate that C. pitcheri mature seed production differs among capitulum positions and that the overall reproductive effort of C. pitcheri is reduced by L. planus. Terminal capitula being the largest and first to develop in C. pitcheri, produced the heaviest and greatest number of mature seeds across all capitulum positions. Capitula with evidence of weevil infestation, however, produced 60% fewer mature seeds and 40% fewer unfilled seeds that were also lighter than those without weevils. Evidence of weevil infestation was also primarily concentrated in secondary and tertiary capitula, which are produced at the tips of first- and second-order branches respectively. Along with information on capitulum contributions to C. pitcheri whole plant fecundity, our report presents one of the first accounts for the position-dependent oviposition of non-native weevil, L. planus, and its direct effects on C. pitcheri seed production.

Cirsium pitcheri是美国和加拿大大湖地区特有的受联邦威胁的多年生单掌多年生蓟树种。人类栖息地的扰动，湖泊水位的波动和气候变化导致C.piteri种群大量减少。非母语象鼻虫种子捕食，Larinus扁平苔藓，也进一步加剧C. pitcheri人口下降和减少其预期的时间要灭绝不到20年。鉴于扁桃体在整个C.piteri范围内的广泛存在，调查其影响的研究对于理解和预测C.piteri的生活史和人口统计学变化至关重要。人口。我们提出了一个为期两年的实地考察，共同花园的实验，检查之间的关系C. pitcheri全厂繁殖力和花序位置和评估的影响L.扁平苔藓上C. pitcheri种子生产。这项研究是正在进行的种群生存力分析的一部分，旨在为C.piteri保护和恢复工作提供信息。我们的研究结果表明，C. pitcheri成熟间花序位置和整体生殖努力种子生产不同C. pitcheri通过减小L.苔癣。头状花序终端是最大的，并率先在发展C. pitcheri，在所有头位上都产生了最大，数量最多的成熟种子。然而，有象鼻虫出没迹象的卡皮图拉（Capitula）产生的成熟种子减少了60％，未填充的种子减少了40％，比没有象鼻虫的种子还轻。象鼻虫侵扰的证据也主要集中在二级和三级头目，它们分别在第一级和第二级分支的尖端产生。随着上花序的捐款情况下pitcheri全株繁殖力，我们的报告介绍了第一占非本地象鼻虫的与位置相关的产卵的一个L.苔癣，并在其直接影响C. pitcheri种子生产。