Environments, spatial structures, and species competitions: determining the impact of yellow-legged hornets, Vespa velutina, on native wasps and bees on Tsushima Island, Japan

Invasive alien species (IAS) can have serious negative impacts on native species in invaded areas. Researchers attempting to measure the impacts of IAS on native species at a landscape level often face challenges though, because the effects of environmental gradients and spatial autocorrelation on population structures are difficult to separate. To evaluate the impacts of IAS, we used spatial filtering and variation partitioning to remove environmental and spatial autocorrelation effects from abundance data for seven native insect species and one IAS, Vespa velutina, on the island of Tsushima, Japan. Here we show that negative correlations among Vespa species persisted after removal of environmental and spatial autocorrelation effects. The fact that alien V. velutina and native Vespa mandarinia japonica showed the strongest negative correlations with other native Vespa species suggested that there were strong competition or/and predation among Vespa species. The ongoing expansion of V. velutina since its incursion indicates that this species may impose strong negative impacts on other Vespa species, but it is possible that the slow expansion of V. velutina to the southern part of Tsushima is due to the presence of other Vespa species that function as a biological barrier. Since most IAS showed spatially structured distributions, especially at the initial stage of the incursion, spatial filtering is a promising tool to evaluate IAS impacts on native species.