Networking: a community approach to invaders and their parasites

Summary There are a number of theories and processes relating to invasive alien species (IAS) and their interactions with natural enemies (predators, parasites and pathogens), including the enemy release hypothesis, spillover and spillback. Most empirical studies focus on pairwise interactions and are limited to the population-level avoiding the complexities of a community approach. Oversimplified studies could result in misleading conclusions because of the importance of positive and negative feedback mechanisms, mediated by parasites, throughout communities and beyond. Recent advances in ecological networks analysis (ENA) provide a powerful framework to investigate the complexity of interactions within ecological communities and response to disturbance, such as the arrival of an IAS. Molecular data, from either standard PCR or next-generation approaches, can be incorporated into ecological networks to enable the number and strength of interactions to be quantified; however, this has rarely been performed so far. In this paper, we explore the contribution of parasite interactions, in the context of community ecology, to the success of invasive alien predatory insects with specific reference to the harlequin ladybird, Harmonia axyridis. We begin by defining the main theories and processes relating to parasite–host interactions in the context of invasion biology, before exploring the advantages of a community ecology approach, and particularly ENA, for revealing dominant mechanisms in determining the success of invasion.