Impact of biotic invasion on predator-prey interactions

Biotic invasion has become one of the most important causes of global change. Although studies on deleterious effects of unintentionally imported species or on the capacity of introduced natural enemies to regulate alien pests have a long tradition, the underlying mechanisms are still poorly understood. This project deals with the Asian earthworm species Amynthas agrestis (Oligochaeta, Megascolicidae), which is currently invading the Great Smoky Mountain National Park. Previous studies have demonstrated that invading earthworms can significantly influence soil structure, alter microbial and mesofauna communities and induce changes in the vegetation cover. In contrast, the knowledge on earthworm-mediated changes in soil macro invertebrate communities is still poor, especially on the interactions between invading earthworms and the native predator community. The proposed project addresses this topic by applying the most recent molecular approaches in gut content analysis. The primary aim is to detect interactions among the new invading earthworm species Amynthas agrestis and the native invertebrate predator community. In addition, we will investigate indirect consequences of earthworm invasion by studying changes in the diet of selected invertebrate predators on the established earthworm community as well as on non-earthworm prey.

National Parks are important refuges for diverse species communities. Increasingly, we observe exotic species introduced by humans, which invade these nature refuges and endanger native species. This study investigated native predators of the Great Smoky Mountains National Park and their reaction to an Asian earthworm species, which was most likely introduced by visitors of the Park. The Asian earthworms are unregularly distributed in the National Park, found mainly near roads and trails and they co-exist with the local earthworm community. The most abundant predators among the ground beetles and the terrestrial salamanders use the Asian intruders as an additional food source, although these exotic earthworms exhibit a striking defense behavior when attacked. Due to earlier findings on the impact of exotic earthworms on the soil structure, native earthworms and plants, we expected a significant influence on the predator community, but this could not be confirmed in this study. Neither the abundance and dominance structure of predators nor their diet was changed due to the presence of the introduced Asian earthworm. The potential danger caused of exotic soil animals is often overlooked due to their hidden life and the difficulties to observe their behavior. In this project, we succeeded to develop and evaluate non-invasive molecular methods, which facilitate the research of trophic interactions among soil animals and at the same time ensure minimal harm on the investigated predators. Avoiding the killing of animals is especially important when working in a nature reserve or when studying endangered species found only in low numbers. This study provided first insights into a highly divers food-web and its resilience, but there is much more to discover. For now the findings are encouraging news for nature refuges, because some exotic organisms obviously are integrated in an ecosystem without causing severe harm to local species communities.