Fencing or Not Wildlife fences are constructed for a variety of reasons including to prevent the spread of diseases, to protect wildlife from poachers , and to help manage small populations of threatened species. Human-wildlife conflict is another common reason for building fences. Wildlife can damage valuable farm animals and crops. Some species carry diseases of agricultural concern, and a few threaten human lives. At the same time, people kill wild animals for food, trade, or to defend lives or property, and human activities destroy wildlife habitat . Separating people and wildlife by fencing can appear to be a _ beneficial way to avoid such harmful effects. But in a paper in the journal Science, published recently, some scientists argue that fencing should only be used if worse comes to worst. According to the scientists, although fencing can have conservation benefits, it also has costs. When areas of wildlife habitat are changed into islands, the resulting small and isolated populations tend towards extinction, and the resulting loss of larger-bodied species can affect interactions between species in ways that cause further local extinctions. Therefore, scientists are asking that conservationists carefully weigh up the biodiversity costs and benefits of new and existing fences. In addition to fences' ecosystem-wide impact, the scientists don't think they always achieve their specific aims. Construction of fences to reduce human-wildlife conflict has been successful in some places but the challenges of appropriate fence design, location, construction, and protection mean that fences often fail to deliver the anticipated benefits. In some places, fences also provide poachers with a ready supply of wire for making traps. A variety of alternative approaches, including better caring for farm animals, community-based crop-guarding, insurance and wildlife-sensitive land-use planning are suggested to reduce conflicts between people and wildlife without the need for fencing. Some projects working with local people and government agencies in Indonesia have shown that human-elephant conflict can be dramatically reduced without using fences. The scientists conclude that as climate change increases the importance of facilitating wildlife mobility and conserving landscape connectivity, fence removal may become an important form of climate change preparation, and so fencing of wildlife should be avoided whenever possible. The main purpose of the passage is to   _  .
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