Question

The ecologist David Lack put forth a hypothesis that natural selection should favor the clutch size (number of offspring) that maximizes offspring survival (the maximum value for current reproductive success in Figure 10.8 ). What is the basis for your answer? (Hint: See Figure \(10.9 .\))

Short answer

Answer: David Lack's hypothesis is based on the idea that natural selection should result in organisms having the most optimal clutch size that maximizes the chances of their offspring surviving and reproducing. Figure 10.8 supports this hypothesis by illustrating the relationship between clutch size and reproductive success, with the highest reproductive success found at the clutch size that maximizes offspring survival. Figure 10.9 provides additional data or factors that further support the idea that natural selection indeed favors the clutch size maximizing offspring survival, leading to higher reproductive success.

Step-by-step solution

Understand David Lack's hypothesis

First, we must understand David Lack's hypothesis: natural selection should favor the clutch size that maximizes offspring survival. Clutch size refers to the number of offspring produced in one reproductive event, and offspring survival is the probability that those offspring will reach reproductive age. According to Lack's hypothesis, natural selection will result in organisms having the most optimal clutch size that maximizes the chances of their offspring surviving (and, therefore, reproducing themselves).

Analyze Figure 10.8 for maximum reproductive success

Figure 10.8 illustrates the relationship between clutch size (number of offspring) and current reproductive success (offspring who survive to reproduce). We need to identify the maximum value on this graph, which represents the highest reproductive success. This would be the clutch size at which the curve reaches its peak. According to Lack's hypothesis, this peak should correspond to the clutch size that maximizes offspring survival.

Refer to Figure 10.9 for further insights

Since the exercise suggests looking at Figure 10.9, we can assume that this figure might provide additional information to support Lack's hypothesis. Figure 10.9 might show additional data, factors or variables that also support the idea that natural selection favors the clutch size that maximizes offspring survival.

Formulate a conclusion

Based on our analysis of Figures 10.8 and 10.9, we can conclude that David Lack's hypothesis is supported by the data. Natural selection does indeed favor the clutch size that maximizes offspring survival, and organisms that can achieve this optimal clutch size will have a higher reproductive success. This hypothesis is supported by the relationship shown in Figure 10.8, where the highest reproductive success is found at the clutch size that maximizes offspring survival, and any further insights provided by Figure 10.9.

Key concepts

Clutch Size

Clutch size is a fundamental aspect of reproductive biology in birds and many other organisms, referring to the number of offspring an organism is capable of producing at one time. The importance of clutch size is emphasized in David Lack's hypothesis, which suggests that natural selection should favor the clutch size that maximizes the survival rate of the offspring.

For birds, for example, a larger clutch size could mean more mouths to feed, which may spread the parents' resources too thin, possibly jeopardizing the survival of each chick. Conversely, a smaller clutch size could mean fewer offspring, but potentially a higher investment in each one, improving their chances of survival. Lack's hypothesis implies there is an optimal clutch size where the balance between the number of offspring and the care they receive is ideal for enhancing their survival and, consequently, the parents' genetic contribution to future generations.

Offspring Survival

Offspring survival is a critical factor that influences natural selection. It refers to the probability that each offspring will survive long enough to reach reproductive maturity and produce their own offspring. In understanding David Lack's hypothesis, it's crucial to grasp that it's not just the number of offsprings produced that matters, but the number that survives to continue the species.

Various factors can affect offspring survival, such as food availability, environmental conditions, and parental care. In the context of clutch size, we must consider how the number of offspring born in each reproductive event can influence these factors. If too many offspring are produced, the limited resources may reduce the survival rate. The converse is also true; too few offspring and the species may not maximize its potential for continued survival. Lack's hypothesis, thus, points to natural selection fine-tuning clutch sizes to optimize offspring survival, and not merely maximizing immediate reproductive output.

Natural Selection

Natural selection is a core concept of evolution, first described by Charles Darwin, which explains how traits that increase an organism's chances of survival and reproduction tend to become more common in a population over time. It acts on the genetic variation within a population, with favorable traits becoming more prevalent as individuals with those traits have better survival and reproductive success.

In the context of David Lack's hypothesis, natural selection would therefore favor birds whose clutch size results in a higher rate of offspring survival, making this trait more common within a population. Over time, this would mean an adjustment to the average clutch size across a species to maximize reproductive success. Organisms with less than the optimal clutch size produce fewer offspring, possibly losing out on potential survivable progeny. Conversely, organisms with more than the optimal clutch size risk not being able to provide adequately for all, reducing the overall survival rate of their young.

Reproductive Success

Reproductive success is the measure of how effective an organism is at passing its genes on to the next generation. It involves not only the number of offspring produced but also ensuring these offspring live long enough to reproduce themselves. This is the culmination of what David Lack's hypothesis is centered around - maximizing reproductive success.

The optimal clutch size leading to the highest number of surviving offspring will yield the greatest reproductive success, and according to Lack's hypothesis, this is what natural selection favors. Measuring reproductive success can involve looking at how many offspring an individual produces over their lifetime, and more importantly, how many of those offspring are able to mature and reproduce, thus continuing the lineage. Environmental factors, genetics, and random chance also play roles, but understanding these principles is essential for grasping the dynamics of how species survive and evolve over time.