Match the column I (Ecologist) with column II (Concept) and choose the correct option.

Robert May told that the global species diversity of earth is about 7 million.A. V. Humboldt observed that within a region, species richness increased with increasing explored area but only up to a limit.David Tilman concluded that plots with more species show less year to year variation in total biomass and increased diversity contributed to higher productivity.Paul Ehrlich explained effect of species extinction by Rivet Popper Hypothesis.