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Explanation:
Invasive species, also called introduced species, alien species, or exotic species, any nonnative species that significantly modifies or disrupts the ecosystems it colonizes. Such species may arrive in new areas through natural migration, but they are often introduced by the activities of other species. Human activities, such as those involved in global commerce and the pet trade, are considered to be the most common ways invasive plants, animals, microbes, and other organisms are transported to new habitats. Most introduced species do not survive extended periods in new habitats, because they do not possess the evolutionary adaptations to adjust to the challenges posed by their new surroundings. Some introduced species may become invasive when they possess a built-in competitive advantage over indigenous species in invaded areas. Under these circumstances, new arrivals can establish breeding populations and thrive, especially if the ecosystem lacks natural predators capable of keeping them in check. The ecological disruption that tends to follow such invasions often reduces the ecosystem’s biodiversity and causes economic harm to people who depend on the ecosystem’s biological resources. Invasive predators may be so adept at capturing prey that prey populations decline over time, and many prey species are eliminated from affected ecosystems. Other invasive species, in contrast, may prevent native species from obtaining food, living space, or other resources. Over time, invading species can effectively replace native ones, often forcing the localized extinction of many native species. Invasive plants and animals may also serve as disease vectors that spread parasites and pathogens that may further disrupt invaded areas. Since the dawn of life on Earth, species have migrated and colonized new areas. In some cases, migrating species were unable to establish sustainable populations in new habitats and quickly died out. In other cases, they either were incorporated into the existing structure of the ecosystem or were responsible for modifying native food chains by out competing native competitors or decimating native prey. One of the most significant species invasions in Earth’s history took place during the Pliocene Epoch (5.3 million to 2.6 million years ago) after the formation of an isthmus connecting North and South America. Numerous predator species migrating from North America to South America are thought to have contributed to the extinction of many of South America’s mammalian species. Since their emergence, modern humans (Homo sapiens) have played an ever-increasing role in species invasions. As a result of their colonization of all but the most extreme of Earth’s ecosystems and their tendency to transform natural environments into agricultural and urban landscapes, modern humans are among the most successful invasive species. However, humans also contribute substantially to the introduction of different species to new areas. Tens of thousands of years ago, migratory bands of humans were accompanied by parasites, pathogens, and domesticated animals. With the rise of civilization, many exotic plants and animals were brought from distant lands to broaden the palettes of consumers or serve as curiosities in gardens and circuses. Although the collection and transport of exotic species dates to ancient times, written records of their ecological effects extend back only a few centuries. One of the best-known historical examples of such species is the Norway, or brown, rat (Rattus norvegicus). This rodent, which is believed to have originated in northeastern China, spread throughout the islands of the Pacific Ocean. Since the rat’s accidental introduction during the voyages of exploration between the late 18th and 19th centuries, populations have established themselves on numerous Pacific islands, including Hawaii and New Zealand, where they prey on many native birds, small reptiles, and amphibians. Some other introductions during this time, however, were deliberate: dogs, cats, pigs, and other domesticated animals were taken to new lands, and there they caused the extinction of many other species, including the dodo (Raphus cucullatus) from Mauritius by 1681. Although invasive species occur on all continents, Australia and Oceania have been particularly hard-hit.
