The signal Hawkeye and the men agreed on while nearing the Huron encampment were three croaks of a crow.
Hawkeye tells his men to scout the area and in the case that they or he find something, they should use the signal in the form of thee croaks of a crow to warn the others about the danger. However, the only thing he finds in the encampment are a couple of Indians.
If the producer were to disappear then all the other organisms will either go extinct, survival of the fittest, or have to adapt to the change.