Final answer:
Sexual reproduction is critical for a population's survival due to the genetic diversity it creates, despite being energetically costlier and potentially slowing population growth in comparison to asexual reproduction.
Step-by-step explanation:
The correct understanding is that sexual reproduction results in offspring with diverse phenotypes, which is crucial for a population's survival in a changing environment, due to the genetic variation it provides. This variation results from the combination of genetic material from two parents, including mutations and the mixing of genes through processes such as crossing over during prophase I and random assortment at metaphase I.
In contrast, the statement that sexual reproduction allows animals to conserve resources and reproduce only during optimal conditions does not accurately represent the role of sexual reproduction, as this strategy actually requires more energy due to the need for finding mates and the metabolic cost of meiosis. The benefits of sexual reproduction include increased genetic diversity, which can lead to a higher chance of adaptation and survival in changing environments, outweighing the energy costs and potential slowdown in population growth when compared to asexual reproduction.