Why is it that the number of eggs is greater in fish and amphibians than in reptiles and birds?

Answer

Hi Peppa,

There are various strategies in the animal kingdom to ensure sufficient offspring. Either they have an enormous number of offspring that are left to their own devices or very little in which a lot is invested: that goes from nutrition to care to education. In the first case, it could be many thousands, and the idea is that there will be a few of them left. The other extreme is one young per litter. It is no different with egg-laying animals. Animals that simply leave their clutches, such as sea turtles, produce far more eggs than animals whose young are fed until they can stand on their own two feet. Many birds are in that case. But even when the clutch is left behind, there are still many variations possible. The amount of nutrients in the eggs can vary enormously from animal to animal and therefore the number of eggs that can be produced at one time also varies. There is thus a very extensive gradient ranging from many offspring in which little is invested per young (egg) to very few offspring in which a lot is invested. In the scientific literature one speaks of the r/K continuum. We also find such a gradient in fish. Mouthbrooders, for example, keep their young for a while and, because of the belt, lay fewer eggs than fish that abandon the young to their fate. There are, of course, other elements at play. Due to the fact that fish live in water, they do not have to invest in systems that prevent desiccation, which is the case with reptiles and birds and which in turn creates opportunities for large clutches.

Kind regards,

Rudy