Pearson Dean E
Rocky Mountain Research Station, USDA Forest Service, 800 E. Beckwith Ave., Missoula, MT 59801, USA.
Oecologia. 2009 Mar;159(3):549-58. doi: 10.1007/s00442-008-1241-5. Epub 2008 Dec 10.
As primary producers, plants are known to influence higher trophic interactions by initiating food chains. However, as architects, plants may bypass consumers to directly affect predators with important but underappreciated trophic ramifications. Invasion of western North American grasslands by the perennial forb, spotted knapweed (Centaurea maculosa), has fundamentally altered the architecture of native grassland vegetation. Here, I use long-term monitoring, observational studies, and field experiments to document how changes in vegetation architecture have affected native web spider populations and predation rates. Native spiders that use vegetation as web substrates were collectively 38 times more abundant in C. maculosa-invaded grasslands than in uninvaded grasslands. This increase in spider abundance was accompanied by a large shift in web spider community structure, driven primarily by the strong response of Dictyna spiders to C. maculosa invasion. Dictyna densities were 46-74 times higher in C. maculosa-invaded than native grasslands, a pattern that persisted over 6 years of monitoring. C. maculosa also altered Dictyna web building behavior and foraging success. Dictyna webs on C. maculosa were 2.9-4.0 times larger and generated 2.0-2.3 times higher total prey captures than webs on Achillea millefolium, their primary native substrate. Dictyna webs on C. maculosa also captured 4.2 times more large prey items, which are crucial for reproduction. As a result, Dictyna were nearly twice as likely to reproduce on C. maculosa substrates compared to native substrates. The overall outcome of C. maculosa invasion and its transformative effects on vegetation architecture on Dictyna density and web building behavior were to increase Dictyna predation on invertebrate prey >/=89 fold. These results indicate that invasive plants that change the architecture of native vegetation can substantially impact native food webs via nontraditional plant --> predator --> consumer linkages.
作为初级生产者，植物通过启动食物链来影响更高营养级的相互作用，这是众所周知的。然而，作为生态系统的构建者，植物可能绕过消费者，直接影响捕食者，产生重要但未得到充分认识的营养级后果。北美西部草原被多年生杂草斑点矢车菊（Centaurea maculosa）入侵后，原生草原植被的结构发生了根本性改变。在此，我通过长期监测、观察研究和田间实验，来记录植被结构的变化如何影响本地结网蜘蛛种群和捕食率。以植被为结网基质的本地蜘蛛，在斑点矢车菊入侵的草原上的总数量，比未入侵草原上的多38倍。蜘蛛数量的增加伴随着结网蜘蛛群落结构的巨大变化，这主要是由皿蛛科蜘蛛对斑点矢车菊入侵的强烈反应所驱动的。在斑点矢车菊入侵的草原上，皿蛛科蜘蛛的密度比原生草原高46 - 74倍，这种模式在6年的监测中一直持续。斑点矢车菊还改变了皿蛛科蜘蛛的结网行为和觅食成功率。在斑点矢车菊上的皿蛛科蜘蛛网比它们主要的原生基质——蓍草（Achillea millefolium）上的网大2.9 - 4.0倍，捕获的猎物总数高2.0 - 2.3倍。在斑点矢车菊上的皿蛛科蜘蛛网捕获的大型猎物也多4.2倍，而大型猎物对繁殖至关重要。因此，与原生基质相比，皿蛛科蜘蛛在斑点矢车菊基质上繁殖的可能性几乎是其两倍。斑点矢车菊入侵及其对植被结构的变革性影响对皿蛛科蜘蛛密度和结网行为的总体结果是，使皿蛛科蜘蛛对无脊椎动物猎物的捕食增加了89倍以上。这些结果表明，改变原生植被结构的入侵植物可以通过非传统的植物→捕食者→消费者联系，对原生食物网产生重大影响。
