The enemy release hypothesis—that the success of invading species is due to release from natural enemies that occur in their home range but not in the new range—can be an important explanation for successful invasions. Testing this hypothesis is difficult, however, because testing requires documented cases of not only successful but also unsuccessful invasions. Therefore, observational data on after-the-fact establishment foll...

It has become increasingly evident that many organisms rely on microbial symbionts for defense against natural enemies, but the ecological importance of defensive symbionts for natural communities still needs to be investigated. A well‐known example is Hamiltonella defensa , a heritable endosymbiotic bacterium commonly found in aphids. Laboratory experiments have shown that H. defensa strongly protects aphids against parasitic...