Insect populations on early successional native and alien plants

Abstract

Alien plants are replacing native plants in many terrestrial landscapes. This study is one of very few to examine explicitly the impact of alien plants on insect communities. Several insect community parameters (biomass, abundance and species richness) were measured in experimentally established early successional communities in Newark, DE, made up of either all native plants or all alien plants. Insects were sampled from six species of native plants and six species of alien plants via bagged whole plant samples and sweep net samples. Native plants produced at least four times more insect biomass per dry leaf biomass than alien plants on three out of four sample dates, with samples taken twice per year over two years. At all sample dates native plants produced significantly higher insect numbers per leaf biomass than alien plants. Species richness was two to three times higher on native plants than on alien plants in sweep net samples, and as much as seven times higher in whole plant samples. Thus, alien plants are not the ecological equivalent of the native plants they replace, particularly in terms of their contributions to the insect-based food web. These results suggest that where alien plants replace at least some of the primary producers in a landscape, there will be a negative impact on the production of phytophagous insects by that ecosystem. This, in turn, is likely to have a negative impact on higher trophic levels, including insectivorous mammals, reptiles, amphibians and birds.