To match the correct individual with their contribution or hypothesis, let's review each person listed along with the contributions mentioned:

Robert May is best known for his pioneering work in theoretical ecology, particularly in the areas of population dynamics and stability in ecological communities. However, none of the choices directly mention these specific contributions. Among the options, the closest (though indirect) could be his theoretical work that touch upon aspects like species diversity estimations.

Alexander von Humboldt, known for his extensive work in biogeography, made critical observations on the geographic distributions of species. His work best correlates with the "Species-Area relationship," which describes how the number of species increases with the area surveyed.

Paul Ehrlich is famous for his work on population studies and environmental issues facing humanity. His statement about the planet's carrying capacity and potential biodiversity loss is widely known. The "Global species diversity at about 7 million" might closely relate to his biodiversity and population studies, though it's not his primary known work.

David Tilman is well-acclaimed for his experimental work on biodiversity and ecosystem productivity. The "Long term ecosystem experiment using outdoor plots" directly correlates with his experimental approach to studying the relationship between biodiversity and ecosystem functioning using field experiments.

Given these associations:

• A (Robert May) might best fit with "Global species diversity at about 7 million" (III) though it's a rough fit.
• B (Alexander von Humboldt) correlating with "Species-Area relationship" (I) is a much clearer connection.
• C (Paul Ehrlich) and the "Global species diversity at about 7 million" (II) matches if we consider his general scope in biodiversity and population dynamics.
• D (David Tilman) with "Long term ecosystem experiment using out door plots" (II) is an exact match for his field of work.

Looking at the options provided,

• Option B: A-III, B-I, C-IV, D-II

This option aligns correctly as per the reasoning.

Therefore, the correct answer is Option B.