What is a series of predictable changes that occur in an ecosystem that lead to the sustainability of life

I’m doing some practice exam questions for biology, and i’m not sure how to do these 3 parts to the question.

Adrought killed all the plants in an agricultural farmland. gradually, due to wind and some birds for. nearby areas, new plants started sprouting l. what stage of succession was taking place in the farmland? a) competition b) nudation c) ecesis d) reaction e) migration

Which statement best compares aerobic and anaerobic respiration