If consumers decrese, the animal that eats them will die off and the animal that eats that one will die off and so forth. Also, the plants will not be under 100% controle.
The reason that the answer is 1/4 is because the young man, his grandfather, his father, and his mother equal 4 people. The young man is 1 person. 1 person/4 people = 1/4.
