Esch Sonja, Klinkhamer Peter G L, van der Meijden Ed
Plant Ecology, Institute of Biology Leiden, Leiden University, P.O. Box 9516, 2300 RA, Leiden, The Netherlands.
Oecologia. 2005 Dec;146(2):218-26. doi: 10.1007/s00442-005-0214-1. Epub 2005 Oct 28.
The effect of spatial habitat structure and patchiness may differ among species within a multi-trophic system. Theoretical models predict that species at higher trophic levels are more negatively affected by fragmentation than are their hosts or preys. The absence or presence of the higher trophic level, in turn, can affect the population dynamics of lower levels and even the stability of the trophic system as a whole. The present study examines different effects of spatial habitat structure with two field experiments, using as model system the parasitoid Cotesia popularis which is a specialist larval parasitoid of the herbivore Tyria jacobaeae. One experiment examines the colonisation rate of the parasitoid and the percentage parasitism at distances occurring on a natural scale; the other experiment examines the dispersal rate and the percentage parasitism in relation to the density of the herbivore and its host plant. C. popularis was able to reach artificial host populations at distances up to the largest distance created (at least 80 m from the nearest source population). Also, the percentage parasitism did not differ among the distances. The density experiment showed that the total number of herbivores parasitised was higher in patches with a high density of hosts, regardless of the density of the host plant. The percentage parasitism, however, was not related to the density of the host. The density of the host plant did have a (marginally) significant effect on the percentage parasitism, probably indicating that the parasitoid uses the host plant of the herbivore as a cue to find the herbivore itself. In conclusion, the parasitoid was not affected by the spatial habitat structure on spatial scales that are typical of local patches.
在多营养级系统中，空间栖息地结构和斑块性的影响在不同物种间可能存在差异。理论模型预测，营养级较高的物种比其寄主或猎物更容易受到碎片化的负面影响。反过来，较高营养级的存在与否会影响较低营养级的种群动态，甚至整个营养系统的稳定性。本研究通过两个田间实验，以寄生蜂广赤眼蜂（Cotesia popularis）为模型系统，研究空间栖息地结构的不同影响。广赤眼蜂是草食动物黄毒蛾（Tyria jacobaeae）幼虫的专一寄生蜂。一个实验研究了寄生蜂在自然尺度上不同距离的定殖率和寄生率；另一个实验研究了与草食动物及其寄主植物密度相关的扩散率和寄生率。广赤眼蜂能够到达距离最远（距最近源种群至少80米）的人工寄主种群。此外，不同距离间的寄生率没有差异。密度实验表明，无论寄主植物密度如何，寄主密度高的斑块中被寄生的草食动物总数更高。然而，寄生率与寄主密度无关。寄主植物密度对寄生率有（微弱的）显著影响，这可能表明寄生蜂利用草食动物的寄主植物作为寻找草食动物本身的线索。总之，在典型的局部斑块空间尺度上，寄生蜂不受空间栖息地结构的影响。
