Impact of invasive Rosa rugosa on the arthropod fauna of Danish yellow dunes

We compared the arthropod fauna of Rosa rugosa patches to the adjacent native yellow dune vegetation by pitfall trapping in the National Park Thy at the Danish North Sea coast. R. rugosa changes the vegetation from a dune grassland (dominated by Ammophila arenaria) poor in flowering plants to a low monospecific shrubbery rich in large flowers. We predicted faunal responses according to the changes in resource availability and environmental conditions promoted by this particular invasive plant: increased populations of flower-visiting insects and species of the phytophagous and detritivorous guilds, and a decrease in thermophilic predator species. A matched-pairs sampling design allowed us to isolate the effects of the vegetation change from those of potentially confounding landscape gradients. The arthropod communities were significantly affected by the vegetation change (redundancy analysis). Six taxa (Opiliones, Lepidoptera larvae, Hymenoptera, Diptera, Tipulidae, Geotrupidae) increased in abundance, and three (Araneae, Staphylinidae, Auchenorrhyncha) were reduced in the rose patches. The main exception from predictions was the lack of effects on large detritivores (isopods, diplopods). Overall, total catches were increased by 45 % in the rose patches, primarily caused by an increase in the abundance of Diptera. Arachnids and carabid beetles were analyzed at species level: the assemblage structure was significantly affected in arachnids but not in carabids. Arachnids showed reduced species richness and diversity and increased dominance in the rose patches, due to reductions among xerotherm species. The results indicate that considerable faunistic impoverishment of thermophilic dune specialist species can be expected in the future if R. rugosa is allowed to continue its invasion across the dune habitat