Although poorly regulated trophy hunting has had a negative impact historically on some wildlife populations, there is wide evidence, including from the International Union for Conservation of Nature (IUCN), that for many threatened species such as the black rhino, white rhino, lion and markhor, well-regulated trophy hunting has brought population increases and reduced larger threats. Conservationists say that when habitats are managed for hunting, it can protect many other endangered species living in the same area. In 2019, 133 leading scientists and community representatives warned in a letter to the journal Science that banning hunting without implementing viable alternatives to protect habitat and generate revenue for local communities would imperil biodiversity.