Question

What happens if the all animals eat only plants

Answer 1

The ecosystem would be unbalanced and the cleaning of nature would not hapn...

Answer 2

basically the earth in which we r living now, the living beings and the flora is  balanced. if all the animals eat only plants then then the flora and the living beings remain unbalanced where the population of the flora would perish and the living beings would dominate. In an ecosystem the plants and the animals must be interdependent on each other, as this balance is disturbed the ecosystem would not be able to survive which leads to an earth with no form of life in it.