A species is considered threatened when the population, or number of organisms of a certain species in an area, begins to decline and is expected to continue to decline. After a population becomes threatened, it is considered vulnerable, endangered or critically endangered depending on the risk of extinction. A species is extinct when there are no more living members of that species. Loss of habitat and human activity (such as hunting, fishing and pollution) are the greatest threats to most species. For now, we can try to help threatened species by preserving their natural habitats, reducing the amount of pollution we put into our environment and changing our behavior.