Invasive Northern red oaks benefit temnothorax crassispinus (Hymenoptera: Formicidae) ant colonies

Non-native plant species can modify their environment, and their influence on food chains is well recognized. How ever, the phenomenon of non-nutrient dependent interaction between non-native plants and native animals has received little attention to date. The Northern Red Oak (Quercus rubra) is a non-native, invasive tree species in Europe, which strongly negatively influences co-occurring plants. However, a part of the native fauna is able to utilize the resources offered by this species in its non-native range. We studied a common species of wood ant, Temnothorax crassispinus, in forests under canopies of non-native Northern Red Oak and native oaks, Pedunculate Oak (Q. robur), and Sessile Oak (Q. petraea). These ants use acorns previously predated by insect larvae as nest cavities. We used the number of workers and number of larvae as a proxy for colony condition. Temnothorax crassispinus benefited from the occurrence of Northern Red Oak; their colonies were significantly more abundant and colony condition was significantly better than under canopies of native oaks. Laboratory experiments confirmed the significant preference of ants for Northern Red Oak acorns compared with native Pedunculate Oak acorns but only if ants had access to whole acorns. We found no significant preference when the choice was restricted to just the cotyledon material of the acorns. This suggests the ability of T. crassispinus to evaluate the solidity of a cavity based on the thicker pericarp of Northern Red Oak acorns. Overall, our data show that T. crassispinus ants benefit from the occurrence of Northern Red Oak in the environment.