Here's why there's variation in fecundity:
* Life history strategies: Different species have evolved different life history strategies. Some species prioritize producing large numbers of offspring with low individual survival rates (e.g., insects, fish), while others invest heavily in a few offspring with high survival rates (e.g., mammals, birds).
* Environmental factors: Fecundity can be influenced by environmental factors such as food availability, predator pressure, and habitat quality. For example, a species may produce fewer offspring in harsh environments with limited resources.
* Species-specific adaptations: Fecundity is often tied to the specific adaptations and characteristics of a species. For example, a species with a high rate of offspring mortality may evolve to produce more offspring to compensate.
Examples:
* Sea turtles: Lay hundreds of eggs in a single nesting event, but only a small fraction of hatchlings survive to adulthood.
* Elephants: Produce one offspring every few years, but invest heavily in parental care, leading to high survival rates.
* Salmon: Spawn thousands of eggs, but many are eaten by predators or die due to environmental conditions.
In summary, fecundity varies greatly between species due to a combination of evolutionary strategies, environmental factors, and species-specific adaptations.