Species introduction woes: How human‐mediated crop transport can influence community dynamics through mutualist displacement

Abstract Agriculturally relevant crop species are universally associated with complex communities consisting of antagonists, commensals and mutualists. When the domesticated species are introduced into new habitats, some community associates can be left behind, and the consequences of such losses can be difficult to study. The cultivated fig Ficus carica and its community of mutualists and antagonists (wasps, nematodes and fungi) provide an excellent system to examine community shifts in this context. Cultivated F. carica can suffer significant losses due to a disease caused by Fusarium fungi. Through demographic surveys of F. carica figs in the USA and their wild European relatives as well as phylogenomic analysis of Fusarium species associated with fig and crop hosts, our research examines how species introductions can influence disease prevalence and severity. We found significant negative correlations between the presence of nematodes and fungi in wild F. carica figs in Europe. We observed similar negative correlations across wild Neotropical figs despite profound environmental differences. These observations suggest that nematodes are key components of fig communities and may directly mitigate or out‐compete pathogenic fungus. Following introduction from its endemic Mediterranean habitat to North America, F. carica crops lost an association with one endemic nematode. Consequently, we found F. carica figs in the USA to have significantly more fungal infestation than their European counterparts. Furthermore, transplantation through North America has introduced multiple novel fungal species into the F. carica system, which likely causes more severe disease for the US fig industry. Synthesis and applications : Similar negative effects associated with community disruption may be a common consequence of the introduction of many domesticated species. While it is difficult in many biological communities to successfully identify important associates and the effects of their potential losses during introduction, the biology of the fig community allows us to examine this context with greater clarity. We argue that fungal diseases in F. carica in the USA could be managed with the re‐introduction of nematodes. Further, nearly all crop species suffer losses due to a Fusarium pathogen, and nematodes may represent an unexpected and cost‐effective method of disease management beyond figs.