Depto Ecologia, Instituto de Ciências Biológicas, Universidade de Brasília, Brasília, DF, Brazil.
Oecologia. 2011 Apr;165(4):1051-62. doi: 10.1007/s00442-010-1783-1. Epub 2010 Sep 25.
The high dependence of herbivorous insects on their host plants implies that plant invaders can affect these insects directly, by not providing a suitable habitat, or indirectly, by altering host plant availability. In this study, we sampled Asteraceae flower heads in cerrado remnants with varying levels of exotic grass invasion to evaluate whether invasive grasses have a direct effect on herbivore richness independent of the current disturbance level and host plant richness. By classifying herbivores according to the degree of host plant specialization, we also investigated whether invasive grasses reduce the uniqueness of the herbivorous assemblages. Herbivorous insect richness showed a unimodal relationship with invasive grass cover that was significantly explained only by way of the variation in host plant richness. The same result was found for polyphagous and oligophagous insects, but monophages showed a significant negative response to the intensity of the grass invasion that was independent of host plant richness. Our findings lend support to the hypothesis that the aggregate effect of invasive plants on herbivores tends to mirror the effects of invasive plants on host plants. In addition, exotic plants affect specialist insects differently from generalist insects; thus exotic plants affect not only the size but also the structural profile of herbivorous insect assemblages.
食草昆虫对其宿主植物的高度依赖意味着植物入侵可以直接影响这些昆虫，要么是因为它们不能提供合适的栖息地，要么是因为它们改变了宿主植物的可利用性。在这项研究中，我们在具有不同程度外来草入侵的塞拉多残余物中采样了菊科的花头，以评估入侵草是否会对食草动物的丰富度产生直接影响，而与当前干扰水平和宿主植物的丰富度无关。通过根据宿主植物专化程度对食草动物进行分类，我们还研究了入侵草是否会降低食草动物组合的独特性。食草昆虫的丰富度与入侵草的覆盖率呈单峰关系，这一关系仅通过宿主植物丰富度的变化来显著解释。多食性和寡食性昆虫的结果相同，但单食性昆虫对草入侵强度的显著负响应与宿主植物的丰富度无关。我们的研究结果支持了这样一种假设，即入侵植物对食草动物的综合影响往往反映了入侵植物对宿主植物的影响。此外，外来植物对专食性昆虫的影响不同于对广食性昆虫的影响；因此，外来植物不仅影响食草动物组合的大小，还影响其结构特征。
