d thông qua một cách cẩn thận và chọn câu trả lời chính xác. Đến năm 2025, trái đất có thể mất nhiều như một phần năm của allspecies được biết đến tồn tại ngày nay. Trong nhiều thế kỷ tại, hàng trăm của loài havedisappeared, hầu như luôn luôn là kết quả của các hoạt động của con người. Passengerpigeon, một ví dụ quen thuộc, là một nguồn thực phẩm cho đến săn bắn quá nhiềuand habitat loss caused its extinction in 1914. The North American bison,whose populations were decimated by settlers and market hunters in the1800s, came close to sharing the same fate. Bison survive today onlybecause of the efforts of early conservationists.Today, species require such efforts more urgently than ever. Anessential task that falls to present-day conservationists is to determine whichspecies are most, endangered, so that conservation resources' can beapplied where action is needed most. Species are categorized by the degreeto which their survival in the wild is threatened. World Wildlife Fund offers asampling of animals and plants that fall mainly within the two most seriouscategories of- threat: critically endangered and endangered. What threatensthese species' existence? Some of the top threats are habitat destruction byunsustainable logging and ever-encroaching human settlement; pollution ofwater, soil, and air by toxic chemicals; unnatural climate changes due tofossil fuel use; unmanaged fishing that exhausts fish stocks; and illegalhunting to supply the demand for skins, hides, traditional medicines, food,and tourist souvenirs. The list which conservationists presents only a fractionof the species at risk of extinction today and does not include thousands ofspecies whose status we do not yet know. Hundreds of species withoutcommon names have been left out, which means that while many mammalsare on this list, only a few insects and mollusks are included. Species listed here range from the largest animal on Earth, the bluewhale, to the majestic tiger, to the humble thick-shell pond snail. Large orsmall, beautiful or ugly, all species play a role in the complex circle of life. Allof us depend on the natural resources of our planet. Each time a species islost, the complexity, natural balance, and beauty of our world is diminished.And what threatens plants and animals ultimately threatens people as well.
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