Along with development comes an increasing interaction with other countries and greater transport of goods and people across the world. This increased globalization often introduces new species at a higher rate. According to the IUCN (2011), invasive species are the second greatest cause of extinction worldwide, and the greatest cause of extinction on islands. They often compete with native species for resources, and many function as harmful pests, pathogens, or predators. Because introduced species were not present when native species evolved, native species have few defenses against them.
Meyerson and Mooney (2007) identify trade and disturbance as major factors of invasion. Trade contributes to invasion by expanding the routes and destinations of global travel, and trade-related technologies have allowed organisms to be transported at greater speeds and in greater quantities than ever before in the history of the planet. By sea, ships take up aquatic species in ballast water at the start of a journey and release them when they empty the ballast at the destination. By air, species often stow away in cargo holds or packing material. Trade can also introduce species intentionally when people import foreign organisms for practical or aesthetic purposes. Disturbance contributes to invasion by lessening competition from existing species and creating new conditions in which opportunistic invaders can thrive. Invasive species often benefit from local disturbances such as soil degradation, as well as global changes, such as increased temperatures, sea level rise, and increased concentrations of CO2.
Hulme (2009) further investigates the economic factors that contribute to the establishment of invasive species around the world. The level of invasion has increased drastically over the past 200 years and the level of international trade has increased in a similar fashion. Furthermore, the amount of invasive species in a region correlates strongly with the GDP of that region, especially on islands. Although species can be introduced into any ecosystem, the risk is higher for areas that are more developed because more sources exist for introduction.
Management of invasive species requires both the removal of species that have already invaded and the prevention of future invasion. To learn more about controlling invasives see Sustainable Management: Invasive Species.