Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
There are a number of characteristic differences between oviparous animals and viviparous animals as described below: oviparous animals are the egg-laying animals. e.g., Fishes, Amphibians, Reptiles & ofcourse the Birds (crow, pigeon etc) . They lay their fertilised egg [which is actually the developing embryo containing yolk-sac and protected by a calcareous shell made up of calcium carbonate (CaCO3)]in their nests or an apparently safer site. But here the eggs are under continuous environmental dangers like predation, killing or eating eggs by their enemies. While the viviparous animals give birth to young ones. The primary developmental stages of developing embryo occurs inside mother's womb i.e., uterus which is a much safer place as compared to the nest (or any other egg-laying site).In viviparous animals, the supply of nutrition to the developing embryo is ensured by continuous nutrients supply via placenta. The waste materials of the embryo is also excreted out by placenta. While in oviparous animals, the stored yolk-sac is the stored nutrients for embryo's development. Their excreta is stored inside the shell.Hence, the oviparous animals are at a greater risk as compared to the viviparous animals. That's why the oviparous animals produce more than one egg at a time to increase their survival chances. Whereas viviparous animals, generally, do not produce more than one egg at a time, as they ensure their survival by continuous nutrients supply, removal of excreta & giving a safer site for their growth and differentiation within mother's womb i.e., uterus.
