Data from: Seed predation has the potential to drive a rare plant to extinction

1. Pre-dispersal seed predation is sometimes considered unlikely to dramatically affect plant population growth because plants are generally expected to produce more seeds than there are safe sites for germination. Lupinus constancei is a rare herb of limited distribution, with fewer than 400 reproductive individuals restricted to a single square kilometre of north-western California, USA. In addition to the vulnerability resulting from its extremely small population size, L. constancei faces heavy seed predation by small mammals.
2. As a stop-gap measure to prevent population decline, managers began covering a large number of the reproductive plants with herbivory exclosures in 2003, but the population-level effects of seed predation and the effectiveness of this caging treatment were unknown. We used ten years of demographic data to compare the population dynamics of plants inside herbivory exclosures with those sustaining ambient rodent seed predation.
3. We found that the stochastic population growth rate would be robust without seed predation (λs = 1.17), but without continued human intervention (i.e. use of exclosures), the current rate of predation would result in a decline towards extinction (λs = 0.92).
4. After our study concluded, high mortality due to two extreme winter droughts followed by a wildland fire reduced the number of reproductive plants to ~103, making extinction of L. constancei more likely.
5. Synthesis and applications. The prevalence of consumer-driven population decline is largely unknown, but this study demonstrates that pre-dispersal seed predation by rodents can have powerful population-level effects, and represents one set of conditions under which consumer pressure has the potential to drive plant extinction. However, with continued management to limit the effects of seed predation in the short-term and investigation into the ultimate drivers of this high seed predation rate in the long-term, the Lassics lupine population could be restored to a robust rate of growth.

1. 散前种子捕食（Pre-dispersal seed predation）通常被认为不太可能对植物种群增长产生显著影响，因为一般认为植物产生的种子数量会多于可供其萌发的安全位点数量。康斯氏羽扇豆（Lupinus constancei）是一种分布受限的稀有草本植物，全球仅存不足400株繁殖个体，且仅局限于美国加利福尼亚州西北部的1平方公里范围内。除了种群规模极小带来的生存脆弱性外，康斯氏羽扇豆还面临小型哺乳动物对其种子的严重捕食压力。
2. 为防止种群衰退，管理者于2003年开始使用植食性动物排除笼（herbivory exclosures）对大量繁殖个体进行覆盖保护，但当时人们对种子捕食的种群级效应以及该笼养措施的有效性尚不明确。本研究利用十年的种群统计数据，对比了植食性动物排除笼内植株与暴露在背景啮齿类种子捕食压力下植株的种群动态。
3. 研究结果显示，若无种子捕食干扰，该种群的随机种群增长率将保持稳定增长（λs = 1.17）；但如果不持续实施人工干预（即使用排除笼），当前的捕食压力将导致种群衰退直至灭绝（λs = 0.92）。
4. 本研究结束后，两次极端冬季干旱以及随后发生的野外火灾导致种群出现高死亡率，繁殖个体数量降至约103株，进一步加剧了康斯氏羽扇豆的灭绝风险。
5. 综合与应用。捕食者驱动的种群衰退的普遍性目前尚不清楚，但本研究证明，啮齿类介导的散前种子捕食可对植物种群产生极强的调控效应，且代表了一类捕食者压力足以推动植物走向灭绝的情景。不过，如果短期内持续开展管理以限制种子捕食的影响，并长期探究该高种子捕食率的根本驱动因素，拉西斯羽扇豆（Lassics lupine）种群有望恢复至稳定增长的状态。