Flowering phenology and compensation for herbivory in Ipomopsis aggregata

摘要

The mechanisms and circumstances that affect a plant's ability to tolerate herbivory are subjects of ongoing interest and investigation. Phenological differences, and the timing of flowering with respect to pollinators and pre-dispersal seed predators, may provide one mechanism underlying variable responses of plants to herbivore damage. The subalpine wildflower, Ipomopsis aggregata, grows across a wide range of elevations and, because phenology varies with elevation, phenological delays associated with elevation may affect the ability of I. aggregata to compensate for or tolerate browsing. Thus, we examined the response of I. aggregata to herbivory across an elevation gradient and addressed the interactions among phenological delays imposed by damage, elevation, pre-dispersal seed predation and pollination, on I. aggregata's compensatory response. Among high and low elevation populations in areas near the Rocky Mountain Biological Laboratory (RMBL) in Gothic, Colorado, we compared the responses of naturally browsed, artificially browsed (clipped), and unbrowsed (control) plants of I. aggregata. We compared responses in the date of initiation of flowering, timing of peak bloom, floral display, nectar production and sugar concentration, oviposition and fruit destruction by the pre-dispersal seed predator Hylemya sp. (Anthomyiidae), fruit production, and aboveground biomass production. Clipping had the greatest effect on reproductive success and clipped plants at high elevation exhibited the lowest tolerance for herbivory. The effects of browsing appear to be mediated by flowering phenology, and both browsing and elevation delayed flowering phenology. Time needed for regrowth delays flowering, and thus affects the overlap with seed predators and pollinators. As a result of delayed flowering, naturally browsed and clipped plants incurred lower rates of seed predation. In the absence of seed predation, plants would exhibit a lower tolerance to herbivory since naturally and artificially browsed plants had fewer fruits destroyed by Hylemya larvae. We provide additional evidence that, for populations near the RMBL, clipping and natural browsing do not have the same effect on I. aggregata plants. This may be due to the selection of larger plants by herbivores. Although under some conditions plants may tolerate browsing, in areas where the growing season is short a phenological delay imposed by damage is likely to significantly reduce plant fitness. Identifying the mechanisms that allow plants to tolerate herbivore damage will help to develop a general framework for understanding the role of tolerance in plant population and community dynamics, as well as plant-herbivore interactions.展开▼

机译：影响植物耐受草食动物能力的机制和情况是人们持续关注和研究的课题。相对于授粉媒介和预分散种子捕食者而言，物候差异和开花时间可能为植物对草食动物损害的可变反应提供了一种机制。亚高山野花，Ipomopsis aaggregata，生长在广泛的海拔高度上，并且由于物候随海拔的变化而变化，与海拔高度相关的物候延迟可能会影响I.aggregata补偿或耐受浏览的能力。因此，我们检查了高海拔食草动物对食草动物的响应，并探讨了由伤害，海拔，预分散种子捕食和授粉所引起的物候延迟对整体食草动物补偿反应的相互作用。在科罗拉多州哥特山的落基山生物实验室（RMBL）附近地区的高海拔和低海拔种群中，我们比较了自然浏览，人工浏览（修剪）和未浏览（对照）植物的整体反应。我们比较了预分散种子捕食者Hylemya sp在开花开始日期，高峰开花时间，花序显示，花蜜产生和糖浓度，产卵和果实破坏方面的反应。 （Anthomyiidae），水果生产和地上生物量生产。修剪对生殖成功有最大的影响，修剪过的高海拔植物对草食性的耐受性最低。浏览的影响似乎是由开花物候学介导的，浏览和海拔升高都延迟了开花物候学。再生所需的时间会延迟开花，从而影响与种子捕食者和授粉媒介的重叠。由于开花延迟，自然浏览和修剪的植物的种子捕食率较低。在没有种子捕食的情况下，植物对草食动物的耐受性会降低，因为天然和人工浏览的植物受Hylemya幼虫破坏的果实较少。我们提供了更多的证据，对于在RMBL附近的种群，修剪和自然浏览不会对总生I. agregata植物产生相同的影响。这可能是由于食草动物选择了较大的植物。尽管在某些条件下植物可能会忍受浏览，但是在生长季节短的地区，由损害引起的物候延迟可能会大大降低植物的适应性。确定允许植物耐受草食动物损害的机制将有助于建立一个通用框架，以了解耐受性在植物种群和群落动态以及植物与草食动物相互作用中的作用。展开▼

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