They exemplify the extreme fuzziness of the concept as it is presently employed. Let me make some remarks on this issue. Biodiversity is a property of a particular geographic area. The first question is thus which areas are to be considered. From a scientific point of view speaking of the biodiversity of e.g. Northern Europe necessarily leads to errors and only the notion of the Earth's biodiversity makes sense.
Biodiversity is measured in particular units.
In order to be able to select the correct measure of biodiversity we must consider how the concept is used. First it has to be established that the employed units are the correct ones in the context of the problem. My third remark is closely connected to this issue. Values are attributed to the units in terms of which biodiversity is measured. The biodiversity of an area is not a 'neutral' property.