Earth is experiencing substantial biodiversity losses at the global scale, while both species gains and losses are occurring locally and regionally. Changes in the biodiversity and composition of ecological communities could profoundly influence ecosystem functions and services. However, few experimental tests have examined the influences of invasive ecosystem engineers, which can have disproportionally strong impacts on native ecosystems. Invasive earthworms are a prime example of ecosystem engineers that influence many ecosystems around the world. In particular, European earthworms invading northern North American forests may cause simultaneous species gains and losses with significant consequences for essential ecosystem processes like nutrient cycling and crucial services like carbon sequestration. Moreover, there is limited knowledge of the global distribution of soil biodiversity, including native and exotic earthworms, their drivers and threats, as well as ecosystem consequences of biodiversity change. Using a synthetic combination of field observations, field experiments, lab experiments, macro-ecological analyses, and meta-analyses, the present project is the first systematic examination of earthworm effects on relationships between plant communities, soil communities, and ecosystem processes. Further, effects of a changing climate on the spread and consequences of earthworm invasion as well as the global distribution of soil biodiversity, including earthworms, were investigated. Results of this research project highlight the pervasive effects of soil biodiversity (particularly invasive earthworms) on relationships between plant communities, soil communities, and ecosystem processes. Invasive earthworms cause substantial reductions of the diversity of soil animals, facilitate the invasion of exotic plants at the expense of native plants, and alter soil physical and chemical properties as well as nutrient cycling. Moreover, it revealed the global environmental drivers of earthworm diversity as well as other soil taxa, highlighting the significant role of climate (precipitation and temperature) determining the distribution of soil organisms at the local to global scale. These findings contributed to the development of a global soil biodiversity monitoring program. The combination of data on (soil) biodiversity and ecosystem functions showed that anthropogenic changes in environmental conditions that affect biodiversity will alter the services provided by ecosystems.
