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Benefiting from the modern transit, people today can easily travel to almost any place on this planet. However, trouble-free transportation also gives a rise to the invasion of imported foreign species. So far, reports have it that imported species usually won’t come in alone: they also bring some negative effects to the host lands. First, some local species can be replaced by newly imported ones and even because extinct under extreme circumstances. This danger emerges mostly riskily in ecological systems that are traditionally isolated from the others. For example, Australia can be one best showcase because the native Australian species are generally considered less competitive in the contest for natural resources, compared with introduced species from other continents. Second, new species also bring dangers to the local ecological system sometimes. For example, cane toad, a species that recently brought into South America from West Africa, has been believed to be responsible for hundreds of poisoning accidents. This is because neither South American people nor native animals have any previous knowledge about this toxic toad and dangers happen once they fail to keep distance away from it. Third, newly introduce species can be economic burden to the local people as well, if not properly handled. For instance, the mesquite tree encounters few natural enemies and spreads rapidly right after its introduction into Africa. Failing to compete with mesquite trees for sunshine and water resource, many local economical plants die off and this is also followed by great reduction in agricultural output. In the lecture, the professor makes several points to demonstrate cases in the passage does not always happen and imported species may be a bliss to local people/ Firstly, in agriculture, it is proved that competitive foreign plants are better substitute of local plants. She then further explains her point by giving an example of maize. He said that maize was not introduced to Asia until recently. But Asian farmers loved maize as soon as they got to know it for maize survive many rigorous environments while local crops need constant care. So even if local species are replaced by newly imported species as the passage concerned, there will not be such a big negative effect. Secondly, after imported species blend into new environment, they will no longer be dangerous to local people and animals. The cane toad does poison people and native animals but they live peacefully in Florida since the local people find out cane toad eats a lot of local pests like flyers and mosquitoes. Thirdly, newly introduce species are not necessarily economic burden to the local people. The professor argues that imported species will bring out positive effects to the host country. Admittedly mesquite trees may cut off light and water resources of local economical plants and cause agriculture output reduction. But the mesquite tree is a precious recourse as firewood for it grows fast, lives short and perfect for burning. Thus, introduced species also benefit the local economics.