Pathogens as Biological Weapons of Invasive Species

Invasive species are nonindigenous species that are introduced into new environments, where they become established and expand their range [1]. They undergo rapid proliferation following the colonization of new habitats, often at the expense of native species, thus having a negative impact on biodiversity. The prospering discipline of invasion ecology seeks to understand why some species become successful invaders, while others do not, even if they are closely related. Pathogens and parasites appear to play an important role in this context. The enemy release hypothesis proposes that invasive species are more competitive in newly colonized habitats because their natural enemies, including pathogens and parasites, are left behind in their native range [2]. Alternatively, the novel weapons hypothesis proposes that invasive species have acquired chemical weapons that provide a selective advantage over their competitors [3]. There is now convincing evidence that the novel weapons hypothesis can be expanded to include pathogens and parasites that are vectored by the invasive species into newly colonized habitats [1]. These pathogens and parasites can act as biological weapons if they infect and kill native competitors.