There are numerous ways that non-native or exotic species can have a negative impact on our environment and the diversity of life on our planet. The statistics are very alarming and more attention should be paid to the problem and finding a solution to the problem before the cost is more than we can bear. When compared with other threats to Biodiversity, the introduction of exotic species ranks second with habit destruction ranking first for being the cause of extinction of species. Secondly, most exotic species cause more damage than pollutants. In fact, almost half of native species in the United States alone are becoming endangered because of exotic species. However, while some introduced species such as certain food crops and our pets like cats and dogs can be beneficial, the majority of others can be very damaging. Native species can only survive in a particular habitat, which is why the largest impact caused by introduced species is that the introduced species changes the whole habitat. For example, most of Florida’s fires are indeed fueled by an exotic tree species called the Australian Paperbark tree, which was imported from Australia and has replaced over 400,000 acres of various native plants such as Sawgrass. Many birds and mammal species declined in abundance as a result of the spreading of the Australian Paperbark tree. Secondly, there are various native species that are endangered by these exotic species being brought in from various countries. I personally feel that we need to protect native populations from dying out. When one native species is eliminated by an exotic species, other species are eliminated and end up becoming extinct and even introduce another new species through the form of hybridization.
http://www.actionbioscience.org/biodiversity/simberloff.html