Population of top level consumers in a particular ecosystem were rapidly decreasing. Further studies revealed that there was also a decline in producers productivity, which other changes happened

Answer

Since the whole ecosystem depends on the primary producers for survival, definitely all the sizes of the population in the ecosystem will be affected. The producers (green plants) makes use of sunlight to supply the needed energy as food substances for the consumers (rabbit) to feed on, and the Consumers is eaten by the top level consumers e. g Leopard.

Therefore, if the population of top level consumers is decreasing, this indicated that the secondary consumers population is reducing, due to reduction in energy obtained from primary producers which has dropped due to the decline in productivity. Hence nothing fort the top consumers to feed on.