Why is the number of offspring decreasing in animal species that care for their offspring? give an example.

If the animal does not take care of the offspring, then most of it dies at different stages of development. Therefore, such animals have numerous offspring to ensure the preservation of the species. Animals that care for their offspring would not be able to protect and feed such a large offspring. For example, a moonfish lays about 6 million eggs, and in a stickleback nest there are no more than a hundred eggs, but the same number of offspring survives to a sexually mature state in both fish.