An endangered species is a population of an organism (usually a taxonomic species), which because it is either few in number or threatened by changing environmental or predation parameters, leaving it at risk of becoming extinct. Many countries have laws offering special protection to these species or their habitats: for example, forbidding hunting, restricting land development or creating preserves. Only a few of the many endangered species actually make it to the official lists and obtain legal protection. Many more species become extinct, or potentially will become extinct, without gaining public notice. The greatest factor of concern is the rate at which species are becoming extinct within the last 150 years. While species have evolved and become extinct on a regular basis for the last several hundred million years, the number of species becoming extinct since the Industrial Revolution has no precedent in biological history. If this rate of extinction continues, or accelerates as now seems to be the case, the number of species becoming extinct in the next decade could number in the millions. While most people readily relate to endangerment of large mammals or birdlife, some of the greatest ecological issues are the threats to stability of whole ecosystems if key species vanish at any level of the food chain.