There are estimated to be more than 1,000 invasive species worldwide and generalists are theorized to be more successful as invaders due to the lack of specialized niches which promotes their success in a wide variety of habitats. While this theory can apply to all aspects of a species’ life history (e.g., habitat preference, resource use, etc.), it may be particularly relevant to non-native species that rely on mutualists during their life cycle. The legume-rhizobia mutualism is an ideal model system to test the hypothesis that non-native species should be mutualistic generalists, as plants in the legume family frequently form mutualistic associations with rhizobia and they are prolific invaders world-wide. Here we perform a meta-analysis using data compiled from 255 articles published between 1984-2014 to answer our question: Are non-native legumes more commonly rhizobial generalists or specialists? For each article, data related to the legume species studied, its rhizobial associates, and study location were manually extracted. The plant species’ provenance in each study location (i.e., native, non-native) was extracted from the Plants of the World database. A T-test was used to determine whether the average number of rhizobial associates differed between native and non-native legumes.
Results/Conclusions
Of the 225 total experiments assessed, 515 different leguminous species were found across 69 countries, with the top 50% of data collected from China, Australia, Senegal, Belgium, the United States, and South Africa. In total, 724 total plants were identified across all studies, as some species were found across multiple articles. Of the 724 total plants, 133 were classified as non-native, and 591 were classified as native in the country they were studied in. There was no significant difference between the number of rhizobia found associating with non-native versus native legumes (p=0.377). These data beg the question of whether the invasive legumes are (1) associating with a select few novel rhizobial associates in their non-native ranges, making them generalists who associate with less rhizobia in non-native ranges, or (2) associating with their preferred rhizobial associates in their non-native range, making them specialists while supporting the theory that all microbial species exist everywhere but at low levels. Determining the path of invasion for legumes provide us with potential opportunities for combating invasive species by using their mutualistic relationships, leading to a decline in the economical and ecological cost of invasive species worldwide.