COS 225-4 - Evolutionary imbalance, colonial history, and global biogeography of naturalized alien plants

Background/Question/Methods

Geographic imbalances in the establishment of alien species have been recognized since the early stages of globalization. To explain the asymmetrical exchange of species among continents, Darwin emphasized that natural selection can only act in response to the selective pressures experienced by species across their evolutionary history. He suggested that geographic barriers divide Earth’s biota into various evolutionary arenas, each with features that influence the intensity of selection. The outcome has been differences in competitive abilities among biogeographic regions and, by extension, species’ capacities to establish in new areas when barriers are removed. This idea has been expanded as the evolutionary imbalance hypothesis (EIH), which proposes that invasion potential should be highest for species originating from 1) large areas able to support large populations and high genetic diversity, 2) regions of high biodiversity where lineages must compete with many others to persist, and 3) stable areas where selection is given ample time to optimize. To test the role of EIH mechanisms in shaping the biogeography of biological invasions, we compiled data on native and alien distributions for the global seed plant flora (n = 336,245, of which 14,461 are naturalized aliens).

Results/Conclusions

After accounting for climate filtering and anthropogenic factors (e.g., economic use of plants and colonial or current links between regions), we find support for the first two EIH mechanisms in driving plant naturalization success globally. Successful aliens tend to come from large, biodiverse biogeographic regions. Support for the stability mechanism was mixed. Our results additionally suggest important links between evolutionary imbalance and plant-human relationships. EIH mechanisms predict which plants have been adopted for economic use, which itself is a primary pathway to naturalization. While association with humans is a key driver of success for plants in the Anthropocene, the ecology and evolutionary histories of plants have likewise shaped the fates of the human cultures that spread them.