plants to grow for food, medicine, pasture, and ornamental uses. They bring animals such as cows, horses, sheep, goats, and pigs for food and work. They also bring companion animals such as dogs and cats. All the organisms mentioned have a history of becoming invasive exotic species in at least one and often multiple cases. For example, northern snakeheads, which are toothy, scaly predatory fish, were released by individuals into ponds in the past few years (Cunningham). They were most likely pets that people decided to ôfreeö into nature. These few releases led to the rapid spread of the fish throughout waterways in the Northeast, and the northern snakehead was found in the Potomac River in 2004, where it now constitutes a major pest (Cunningham).
Once a species arrives in a new habitat, a number of things may happen. It may die out, reproduce in a limited capacity, or cause a maj
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