Question

why do most food chains consists of four steps?

Answer 1

producer---primary consumer-----------secondary consumer----------tertiary consumer----top carnivore
ex:grass--------rabbit-----------fox----wolf

Answer 2

Because of ten Percent Law.Energy reduces by 10% when it goes to next Tropic level in food chain. For example 
            Grass-------- Grasshopper------------rabbit-------snake ----eagle .
Eagle will have the last energy .so that is why food chains have only 3-4 steps .