How do ecologists estimate the total number of species present in the world?

Explanation

It is difficult to answer that how many species are there on earth. According to the IUCN (International Union of Conservation of Nature), the total number of animal and plant species is more than 1.5 million. It is doubtful that how many of the species are yet to be discovered and described. For many taxonomic groups, species inventories are more complete in temperate than in tropical countries. Many of the species waiting to be discovered are in the tropics. Biologists often make statistical comparison of the temperate-tropical species richness of the studied group of insects and tried to calculate this ratio to other groups of plants and animals in order to provide gross estimate of the total number of species on earth. Accordingly Robert May explained that the total global species biodiversity is around 7 million.