During one mating of frogs, the female lays 2.000 to 3,000 eggs in water as the male sheds millions of sperm over them. How do these large numbers relate to the frog's fitness for life in water?

The large numbers of sperms and eggs means that there is almost a guarantee of fertilization and with so many tadpoles at, least quite a number will reach adulthood, because of the predators the frogs have some are eaten at a young age and therefore do not reach adulthood. In other terms, the large numbers of eggs and sperms increases the frogs chances of survival.