Abstract
1. Introduced species disrupt native communities and biodiversity worldwide. Parasitic infections
(and at times, their absence) are thought to be a key component in the success and
impact of biological invasions by plants and animals. They can facilitate or limit invasions,
and positively or negatively impact native species.
2. Parasites have not only direct effects on their hosts, but also indirect effects on the species
with which their hosts interact. Indirect effects include density-mediated effects (resulting from
parasite-induced reduction in host reproduction and survival) as well as trait-mediated indirect
effects (resulting from parasite-induced changes in host phenotype, behaviour or life history).
These effects are not mutually exclusive but often interact.
3. The importance of these indirect interactions for invasion success, and the extent to which
these effects ramify throughout communities and influence ecosystems undergoing biological
invasion provide the focus of our review. Examples from the animal and plant literature
illustrate the importance of parasites in mediating both competitive and consumer–resource
interactions between native and invasive species.
4. Parasites are involved in indirect interactions at all trophic levels. Furthermore, the indirect
effects of parasitic infection are important at a range of biological scales from within a host to
the whole ecosystem in determining invasion success and impact.
5. To understand the importance of parasitic infection in invasion success and in the outcomes
for invaded communities requires an interdisciplinary approach by ecologists and parasitologists,
across animal and plant systems. Future research should develop a framework integrating
community ecology, evolution and immunology to better understand and manage the
spread of invasive species and their diseases.