Volume 12 (2017) Issue 1 Pages 52-64
Plant and arthropod communities interact closely with one another, therefore, invasive plants can alter not only plant communities, but may also have direct and indirect effects on arthropod communities. Here, we focus on the exotic giant ragweed, which is a serious invasive weed in Japan. Recently, the exotic plant invaded and has dominated part of a semi-natural grassland in Sugadaira Montane Research Center (Nagano Prefecture, Japan). We attempted to evaluate the potential impact of the invasive plant on both plant and arthropod communities by comparing the community composition, abundance, species richness and diversity indices of plants and arthropods between areas where the exotic giant ragweed had and had not invaded, referred to as the invaded and reference areas respectively. We found significant differences in plant and arthropod community compositions between the areas. Plant species richness was lower in the invaded area as predicted. However, the abundance of arthropods including herbivores was higher in the invaded area compared to the reference area in contrast to the expectation that plant invasions reduce arthropod abundance and diversity. We discuss potential causes of the unexpected results.