Chapter 31, Problem 36A

Summary Introduction

To write:

Comparison between the strategies of spending reproductive energy by producing large numbers of eggs with little or no parental care, and producing a smaller number of eggs and engaging in nurturing behavior.

Examples of animals using each type of strategy.

Introduction:

Reproductive effort is defined in terms of the energy allocated by the organisms to the process of reproduction for one season or one reproductive event. It also includes the energy proportionate into an individual offspring.

Explanation of Solution

Reproductive energy of an individual organism includes the energy invested by the female and the energy sanctioned to each offspring. Heavy energy investment in a single event of reproduction is an expensive process.

An organism producing a large number of eggs at a single time and not providing parental care ensures less investment of energy. Energy is only spent on laying the eggs. Although the number of eggs laid is higher, it requires a lesser investment of energy than laying a lesser number of eggs multiple times. Since negligible or little parental care is provided, the energy spent in raising the offspring becomes even lesser. The offspring are expected to be self-sufficient in most cases.

On the other hand, an organism producing a smaller number of eggs and engaging in nurturing behavior will spend a greater amount of energy on raising each individual offspring. Lesser energy is spent on producing the offspring than on raising them. Once the individual is produced, the mother invests a lot of energy on raising and taking care of the offspring, sometimes at the expense of her own health.

Sea snails (whelks) and sea urchins are animals that produce a large number of offspring at a time (200-300 and 10,00,00,000 eggs respectively). The offspring produced are very self-sufficient since birth and are able to take care of themselves.

Amphibians like salamanders and frogs spend a lot of their energy on the eggs and the hatchlings.

Conclusion

An animal producing lesser number of offspring but providing a lot of parental care not only exceeds its energy capacity but also decreases its life expectancy. On the other hand, an animal producing greater number of eggs will spend lesser amount of energy and produce self-sufficient offspring.