Fires have also become more frequent and often result in irreversible damage to ecosystems, particularly forests. Other threats to species include habitat change, pollution, direct competition with livestock, and the spread of invasive species and diseases. Many of the remaining populations of species listed in the 2007 national Red Book are at the critical lower limit of viability, from w'hich the populations may not be able to recover. The tiger population became extinct at the turn of the twentieth century, and now the otter faces a similar fate. Even species thought of as common, such as pheasants and wild boar, were completely exterminated in many regions, but have since been reintroduced in some areas. Marmots have declined significantly over w'ide areas as a result of overhunting and eradication campaigns, and have completely disappeared from some areas of their range.