As an economist the whole bio-diversity loss argument is not as simple as you might think. If some obscure mammal, bird on insect dies out in Brazil due to de-forestation what is the economic cost to you and me? Arguably nothing expect the extraordinary long odds that one of these species held the key to the cure for cancer of some equally scary disease and the "love of variety" argument where we gain utility from seeing said insets or birds in real life or more likely on television. This has to weighed against the economic reasons for the original loss - in this case deforestation which occurred in the first place due to the economic necessity of local people who are just trying to survive.
The fishery issue is slightly different and is what is alluded to in this article. Clearly if fish stocks fall below a certain level it will impact on the food resources for millions. This is already happening but is less about bio-diversity and more about over fishing.
Germany Warns Of Economic Risks From Species Loss [PlanetArk]
BERLIN - Nations must act to slow extinction rates, German Environment Minister Sigmar Gabriel said on Thursday, arguing the loss of species threatened food supplies for billions of people.
Gabriel, due to open the Bonn summit, pointed to marine life as an example.
"If we don't do anything, there won't be any more commercial fishing by 2050. Imagine what that means for the world's food supplies," Gabriel said, noting several billion people rely on protein from fish to survive.
UN experts say human activity, including the emission of greenhouse gases, threatens to cause the worst spate of extinctions on earth since the dinosaurs died out 65 million years ago. Some experts say three species disappear every hour.