del-Val Ek, Crawley Michael J
Department of Biological Sciences, Imperial College London, Silwood Park, Buckhurst Road, Ascot, Berkshire, SL5 7PY, UK.
Oecologia. 2005 Jan;142(2):202-11. doi: 10.1007/s00442-004-1719-8. Epub 2004 Oct 9.
Competition and herbivory are two of the main forces shaping plant communities. Although several studies have investigated their impact on plant populations separately, few investigations have examined how they might interact. With the purpose of clarifying the combined roles of competition and herbivory on herb biomass in a grassland, we assessed the effects of different herbivores with reduced grass competition. We conducted a field experiment in 2000-2001 in a British acid grassland (Oak Mead), where we experimentally reduced grass biomass and excluded rabbits, insects and molluscs in a factorial design. Removing the grasses from Oak Mead dramatically increased herb biomass and total above-ground biomass. Herbivore exclusions (i.e. rabbits, insects and molluscs) did not affect total above-ground biomass, but they altered relative abundance of several species. Grass removal and rabbit exclusion had positive interactions on biomass of several herb species, and there were some subtle interactions between different herbivore groups: monocots benefitted when both rabbits and molluscs were excluded, and some herb species had greater biomass when insects and rabbits were absent. We then compared the results with a 10-year experiment that manipulated similar variables in neighbouring grassland (Nash's Field). The comparison between Oak Mead and Nash's Field showed that cessation of herbicide application returns the system to its previous state of grass dominance after 3 years. Therefore, even when herbs were more abundant, they could not prevent reinvasion of the grasses once external factors were removed.
竞争和食草作用是塑造植物群落的两大主要力量。尽管已有多项研究分别调查了它们对植物种群的影响，但很少有研究探讨它们之间可能的相互作用。为了阐明竞争和食草作用对草原草本植物生物量的综合作用，我们评估了不同食草动物在减少草本植物竞争情况下的影响。2000年至2001年，我们在英国的一片酸性草原（橡树草地）上进行了一项田间试验，采用析因设计，通过实验减少草本植物生物量，并排除兔子、昆虫和软体动物。去除橡树草地的草本植物显著增加了草本植物生物量和地上总生物量。排除食草动物（即兔子、昆虫和软体动物）并未影响地上总生物量，但改变了几种物种的相对丰度。去除草本植物和排除兔子对几种草本植物的生物量有正向相互作用，不同食草动物群体之间存在一些微妙的相互作用：当兔子和软体动物都被排除时，单子叶植物受益，当昆虫和兔子不存在时，一些草本植物的生物量更大。然后，我们将结果与在相邻草原（纳什田野）进行的一项为期10年、操纵类似变量的实验进行了比较。橡树草地和纳什田野的比较表明，停止施用除草剂3年后，该系统恢复到以前草本植物占优势的状态。因此，即使草本植物更为丰富，一旦外部因素消除，它们也无法阻止草本植物的重新入侵。
