To ensure that at least a few eggs are fertilised and survive despite exposure to predators and environmental factors.
Explanation
The number of eggs produced by an organism is an evolutionary adaptation correlated with the mode of fertilization (external vs. internal) and the probability of offspring survival in the external environment.Detailed Analysis:
- External Fertilization and Environmental Exposure: Aquatic animals such as frogs and fish typically undergo external fertilization, releasing gametes directly into the water. These eggs lack protective hard shells and are exposed to environmental factors such as water currents, wind, and rainfall.
- High Mortality Risk: Because the eggs and sperm are released into an open environment, many fail to meet for fertilization. Furthermore, the fertilized eggs are highly vulnerable to predators.
- Compensatory Mechanism: To ensure the continuity of the species, these animals lay hundreds or thousands of eggs. This high quantity compensates for the high mortality rate, ensuring that at least a few individuals survive to adulthood.
- Contrast with Internal Fertilization: Animals like hens undergo internal fertilization. Their eggs are protected by hard calcareous shells and are often cared for by the parent, resulting in a much higher survival rate. Consequently, they do not require the production of large numbers of eggs.
Key Takeaway: Organisms undergoing external fertilization produce large numbers of eggs to offset the high probability of destruction by predators and environmental factors, whereas internal fertilization allows for fewer eggs due to higher survival rates.