Parasites and Biological Invasions: Predicting Ecological Alterations at Levels From Individual Hosts to Whole Networks

The network approach is increasingly used by food-web ecologists and ecological parasitologists and has shed light on how parasite-host assemblages are organized, as well as on the role of parasites on the structure and stability of food webs. With accelerating rates of nonnative parasites being introduced around the world, there is an increasing need to predict their ecological impacts and the network approach can be helpful in this regard. There is inherent complexity in parasite invasions as parasites are highly diverse in terms of taxa and life strategies. Furthermore, they may depend on their cointroduced host to successfully overcome some crucial steps in the invasion process. Free-living introduced species often experience enemy release during invasion, which reduces the number of introduced parasites. However, introduced parasites that successfully establish may alter the structure of the recipient network through various mechanisms including parasite spill-over and spill-back, and manipulative and nonmanipulative phenotypic alterations. Despite limited literature on biological invasions in infectious food webs, some outstanding methodological issues and the considerable knowledge gaps that remain, the network approach provides valuable insights on some challenging questions, such as the link between structure and invasibility by parasites. Additional empirical data and theoretical investigations are needed to go further and the predictive power of the network approach will be improved by incorporating weighted methods that are based on trophic data collected using quantitative methods, such as stable isotope analyses.