In the late 1800’s and early 1900’s, there were few laws against imports and exports between countries, which allowed legal trading of many plants, animals, and insects between many countries. Despite more stringent laws, the United States still imported $2.3 million worth of goods in 2018. The associated introduction of new species to the U.S. caused an increase in invasive and pest species that have expanded across the country. Here we ask how much further the top twenty terrestrial invasive and pest species can spread in the United States. To address this, we collected distribution and habitat information about the top twenty invasive terrestrial species across the United States. Climate data for each county within the States was also compiled using the eight most pertinent BioClim variables 1, 2, 5, 6, 7, 12, 13 and 14. Next, we used the R statistical program and the distribution and climate variables to build niche suitability models for each invasive species in the United States.
Results/Conclusions
Among the twenty terrestrial species we studied, sixteen were plants, three were animals, and one was an insect. Of these species, fifteen plants, one animal, and the sole insect were found to be at high risk of invading nearly every county in the U.S. based on their climate variables. Of the 3 animals, 2 are not able to inhabit any counties in Hawaii and one of the plants is not able to inhabit either Alaska or Hawaii. The extreme weather in Alaska may make it hard for these species to survive. Due to Hawaii being an island, these species also face challenges invading its counties. 17 out of the 20 overall species were found to match with 2988 counties out of the 3007 counties in the U.S. This was expected due to the species’ broad niches, which is likely a big component of their invasive success. Most of the species we studied have invaded large portions of the U.S. already and our models show that they will continue to spread. Future models should work to incorporate species interactions, however the enemy release hypothesis and their current widespread establishment suggests that this may not be as important as the abiotic habitat factors we focused on here.