, the correct matches are as follows:

• (A) Robert May: He provided a conservative and scientifically sound estimate that global species diversity is approximately 7 million .
• (B) Alexander von Humboldt: During his explorations in South American jungles, he observed the species-area relationship, noting that species richness increases with the explored area up to a specific limit .
• (C) Paul Ehrlich: This Stanford ecologist used an airplane analogy to propose the rivet popper hypothesis, which explains how the loss of species (rivets) can impact ecosystem (airplane) stability and functioning .
• (D) David Tilman: He performed long-term ecosystem experiments using outdoor plots, discovering that communities with more species exhibited higher productivity and less year-to-year variation in biomass . Following these matches results in the sequence (A)-(III), (B)-(I), (C)-(IV), and (D)-(II).