Carson Walter P, Root Richard B
Section of Ecology and Systematics, Corson Hall, Cornell University, Ithaca, NY 14853, USA, , , , , , US.
Oecologia. 1999 Nov;121(2):260-272. doi: 10.1007/s004420050928.
We tested the hypothesis that phytophagous insects would have a strong top-down effect on early successional plant communities and would thus alter the course of succession. To test this hypothesis, we suppressed above-ground insects at regular intervals with a broad-spectrum insecticide through the first 3 years of old-field succession at three widely scattered locations in central New York State. Insect herbivory substantially reduced total plant biomass to a similar degree at all three sites by reducing the abundance of meadow goldenrod, Solidago altissima. As a result, Euthamia graminifolia dominated control plots whereas S. altissima dominated insecticide-treated plots by the third year of succession. S. altissima is the dominant old-field herbaceous species in this region but typically requires at least 5 years to become dominant. Past explanations for this delay have implicated colonization limitation whereas our data demonstrate that insect herbivory is a likely alternative explanation. A widespread, highly polyphagous insect, the xylem-tapping spittlebug, Philaenus spumarius, appeared to be the herbivore responsible for the reduction in standing crop biomass at all three sites. Insect herbivory typically caused little direct leaf tissue loss for the ten plant species we examined, including S. altissima. Consequently, the amount of leaf area removed was not a reliable indicator of the influence of insect herbivory on standing crop biomass or on early succession. Overall, we found a strong top-down effect of insect herbivores on biomass at several sites, so our results may be broadly applicable. These findings run counter to generalizations that top-down effects of herbivores, particularly insects, are weak in terrestrial systems. These generalizations may not apply to insects, such as spittlebugs, that can potentially mount an effective defense (i.e., spittle) against predators and subsequently reach relatively high abundance on common plant species. Our results suggest that insect herbivory may play an important but often overlooked role during early old-field succession.
植食性昆虫会对早期演替的植物群落产生强烈的自上而下的影响，从而改变演替进程。为了验证这一假设，我们在纽约州中部三个分散的地点，在旧耕地演替的前三年，定期使用广谱杀虫剂抑制地上昆虫。通过减少草地一枝黄花（Solidago altissima）的数量，昆虫取食在所有三个地点都将总植物生物量大幅降低到了相似程度。结果，到演替的第三年，在对照样地中一枝香（Euthamia graminifolia）占主导，而在杀虫剂处理的样地中草地一枝黄花占主导。草地一枝黄花是该地区旧耕地的优势草本物种，但通常至少需要5年才能成为优势种。过去对这种延迟的解释涉及定居限制，而我们的数据表明昆虫取食可能是另一种解释。一种广泛分布、多食性的昆虫，吸食木质部的沫蝉（Philaenus spumarius），似乎是导致所有三个地点现存作物生物量减少的食草动物。对于我们研究的十种植物，包括草地一枝黄花，昆虫取食通常很少造成直接的叶片组织损失。因此，去除的叶面积量并不是昆虫取食对现存作物生物量或早期演替影响的可靠指标。总体而言，我们发现食草昆虫在几个地点对生物量有强烈的自上而下的影响，所以我们的结果可能具有广泛的适用性。这些发现与食草动物，特别是昆虫在陆地系统中的自上而下影响较弱的普遍观点相悖。这些普遍观点可能不适用于沫蝉等昆虫，它们可能会对捕食者形成有效的防御（即泡沫），随后在常见植物物种上达到相对较高的丰度。我们的结果表明，昆虫取食可能在旧耕地早期演替过程中发挥重要但常被忽视的作用。
