Animals play different roles in our ecosystem. If one species disappears, it will affect the whole ecosystem. For e.g. In a forest, if the deer (primary consumer) disappears, it will affect the population of the lions as well as plants. The plants will overgrow as there is no one to eat them and the lion species will die of starvation. Or is lion (secondary consumer) disappears, it will affect the deer population as well as plant population. The deer population will increase alarmingly and they will eat all the plants. Then they will start eating our farmlands. When all the plants are gone, they too will die of starvation. Thus, every animal species is important for our ecosystem.