Non-native species is a commonly used term for plants and animals introduced into a foreign environment, primarily by humanity, either intentionally or accidentally. These exotic invaders die because they cannot adapt to the environment. introduced ecosystem, which implies that they involve domestication. However, some thrive to the point of dominating their new ecosystem by spreading quickly and widely. These types of invaders have no native predators and, over time, take over the ecosystem from native species (David and Sweeney 53). The term invasive can also refer to introduced species and diseases. To date, approximately 50,000 non-native species have been introduced into the United States. Non-native species may be classified as invasive if they pose a danger to ecological systems. Introduced species that humans must care for in order to thrive are called ornamental plants. In addition to human activities, non-native species may be introduced by climate change due to natural selection by which new organisms capable of survival become established. Continental drift is another factor known to contribute to the presence of non-native species. However, these are slow processes and the most common is human activity. Over the past centuries, immigration has occurred on a global scale, with man moving to extremely distant destinations, where his movements gave way to the transportation of plants as well as other organisms to environments completely new, far from their original ecosystem. To protect these ecosystems, native species, and the United States economy, the respective authorities have designed regulatory measures intended to control the introduction of new alien species by humans. Invasive species face extremely strict measures imposed on them despite...... middle of paper ......häuser, 2005. PrintMolnar, L., Rebecca L. Revenga, G . & Mark, D. Assessing the global threat of invasive species to marine biodiversity. Frontiers of ecology and environment. 6.9 (2008): 485-92 Richardson, D M. Fifty years of invasion ecology: the legacy of Charles Elton. Chichester, West Sussex: Wiley-Blackwell, 2011. Print.Roman, J. & John A. Paradox lost: genetic diversity and aquatic invasion success. Trends in Ecology and Evolution 22.9 (2007): 454-64. Venner, Marie. Control of invasive species: a summary of road practices. Washington, DC: Transportation Research Board, National Research Council, 2006. Print. Regulating live animal imports into the United States: Wildlife Defenders. New England Herpetological Society, Inc. 2005-2014. Internet. March 9 2013.