They also spend more energy and time trying to keep cool. All of this energy and time is not available for other things, like reproduction. Moreover, during the dry season, when food is scarce, some may starve. Those that starve of course can't reproduce the next year. Over time, all of the individuals in the population will be descendants of the individuals with the lower metabolic rate, and they will carry copies of their genes .
Natural selection produces adaptations that enhance survivorship, reproduction, or both.
Because fitness is the ultimate measure of how many genes an organisms passes on, and it incorporates both survival and reproduction, we will discuss adaptations in terms of life histories . Life histories describe the characteristics of organisms that allow them to balance the costs and benefits of expenditures for survival and reproduction in such a way as to maximize fitness. As we saw in the lecture on behavior, mating often involves elaborate displays for the attraction of mates. These displays may also attract predators. Delaying mating may prolong life, but it has no genetic payoff.