Consider a stable frog population living at carrying capacity in a pond. If an average female produces 6,000 eggs during her lifetime and an average of 300 tadpoles hatch from these eggs, how many of these tadpoles will, on average, survive to reproduce?
1 female tadpole will survive to reproduce on the average. ( The ratio of males to females in the population is not stated.)
The population is stable which means the population is neither increasing nor decreasing. That means that the population is replacing itself.
The given female may not have any of tadpoles survive to reproduce. Another female might have two or three tadpoles reproduce. On the average one female tadpole will survive to replace the population.
Natural selection plays a part. If the water in the pond is dark green tadpoles that are dark green will have a greater chance of survival. The genes have a limited ability to adapt, so even as the population of frogs stabilizes the gene variation will also stabilize to the given environment.