Between 1900 and 2015, nearly half of 177 surveyed mammal species lost more than 80 per cent of their distribution. Billions of populations of mammals, birds, reptiles and amphibians have been lost all over the planet, prompting scientists to suggest we have now entered a sixth mass extinction. This has been due to rapid increase in human population and the overuse of natural resources. The current species extinction rates are estimated to be 100 to 1,000 times faster than in the pre-human times and our activities are responsible for the faster rates. Ecologists warn that if the present trends continue, nearly half of all the species on earth might be wiped out within the next 100 years.