$(a)$ If all producers are removed then primary productivity will be decreased. Therefore biomass will not be obtained to next successive/sequential higher equatorial trophic level or heterotrophic organisms.

$(b)$ If all herbivores organisms are removed primary productivity and biomass of producers will increase and carnivores animals will not be survived due to animals are not obtained as food.

$(c)$ By removing higher carnivores there would be disturbance in ecosystem because herbivores will be increased in number which destroy trees and produce desert region.