摘要
Plants typically experience great losses from their reproductive potential represented by ovule production to the post-dispersal crop of viable seed.We examined seed density and viability in a founder population of mountain birch(Betula pubescens ssp.tortuosa),aiming to quantify losses at different stages and examine potential selection forces on the reproduction success of the founder generation of an isolated population.At the time of the study(2017-2020),the population had recently reached reproductive maturity,following its colonization around 1990 through long-distance dispersal onto an early successional outwash plain in southeast Iceland.Seed densities were high,but 89% of apparently intact seeds did not contain an embryo,despite being visually indistinguishable from filled seeds.Externally evident losses amounted to about 45% of the total seed crop and were mostly due to predation by the gall midge Semudobia betulae.When all losses were accounted for,2.7% of the seed crop remained viable and germinated.Pollen limitation may partially explain the high incidence of empty seeds.Excessive flower production is compatible with the predator satiation hypothesis but cannot explain pre-dispersal losses.Another adaptation to predation,masting,appears poorly developed in Iceland.Our results suggest the presence of constraints on the reproduction potential of the new island population,that are more limiting than in neighbouring populations,and we discuss their developmental,ecological,and environmental correlates.
植物通常会经历从胚珠生产到扩散后可存活种子的大量繁殖潜力损失。本研究中,我们探究了高山桦(Betula pubescens ssp.tortuosa)的一个创始种群的种子密度和活力,旨在量化不同阶段的损失,并检验对孤立种群创始世代繁殖成功的潜在选择压力。在研究期间(2017-2020年),该种群在约1990年通过远距离传播到冰岛东南部一个早期演替的冲积平原后,刚刚达到生殖成熟。种子密度很高,但89%的表面完整种子并不包含胚胎,尽管它们在外观上与饱满种子无法区分。外部明显的损失约占总种子产量的45%,主要是由于瘿蚊(Semudobia betulae)的捕食。综合所有损失后,2.7%的种子产量仍可存活并能发芽。花粉限制可能部分解释了空种子的高发生率。过度的花朵生产符合捕食者饱和假说,但无法解释扩散前的损失。另一种对捕食适应的机制,即间歇性结实,在冰岛表现出较差的发展。上述结果表明,新岛种群的繁殖潜力存在比邻近种群更为限制的约束,本文讨论了其发育、生态和环境相关性。
基金
supported by the Icelandic Research Fund(173688).
