Invasive Species in the United States

Human migrations over thousands of years have dramatically altered the earth's landscapes. One way that this has been keenly felt is through the transportation of exotic invasive species across geographic borders. This movement of plants, animals, fungi, bacteria, and viruses has had an enormous economic impact on humans and has caused large-scale disruptions to ecosystems, including loss of both habitats and species. While land managers have long struggled with the impact of invasive species, controlling the problem has come into national focus only in the past few years as the large scope of economic and environmental issues has come more into public view. Solutions to invasions have been tried with limited success. However, continued efforts are yielding some measure of control and are therefore worth pursuing.

In order to understand how and why species invasions come about, it is necessary to view the historical transport of species in parallel with human migrations. As humans migrate, they bring more with them than just luggage they consciously select. They also inadvertently carry along other organisms. For example, they bring human diseases within their own bodies. Their luggage and food stores for the journey may contain seeds from local plants. If they bring animals with them, such as cattle and horses, these animals may harbor seeds in their hoofs. Especially if animal feed is brought along (hay

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new habitats and gain a foothnld that allows them to expand. Another explanation as to what makes a species able to invade a new habitat is that diseases and predators that were present in its native habitat are not found in the new habitat. Two studies that examined 499 species found that invasive species have fewer infections and predators in their new homes that they did in their native environments (ôInvadedàö). This is not surprising to land managers and scientists who have long observed the differences between invaders in their natural and adopted habitats. Species contain natural parasites, such as bacteria, fungi, and insects that they have co-evolved with over many years. If those pest organisms are not brought with the species in question, that species will have a competitive advantage over the native species in the new habitat that will allow the invader to spread. Meanwhile, the native species are burdened with their own particular parasites, which limits the resources they can use to compete with the invader. This is what gives the invader its advantage. The same is true with predators. If a population is being kept under control by predators in its native territory, it will co-exist with other species there and not o
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Approximate Word count = 2450
Approximate Pages = 10 (250 words per page)

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