The figure below shows how reproductive fitness varies with tail length in a bird species. Given this pattern, what kind of selection is most likely to act on tail length in this population? 
To determine what type of selection is acting on tail length in this bird species, we need to analyze the given graph that relates reproductive fitness to tail length.
On analyzing the graph, we observe:
- The fitness is lowest at intermediate tail lengths.
- The fitness is higher at both the shorter and longer extremes of tail length.
This pattern indicates Disruptive Selection, where individuals with extreme trait values on both ends have higher fitness compared to individuals with intermediate values.
Let's evaluate each option:
- Relaxed Selection: This type typically refers to a reduction in selective pressure, allowing increased variance in a trait. It does not fit the observed pattern.
- Directional Selection: Typically favors one extreme over the others, shifting the average value of the trait in one direction. This does not align with the observed pattern, where both extremes are favored.
- Disruptive Selection: This selection favors individuals at both extremes over those with intermediate traits, matching the observed fitness pattern.
- Stabilizing Selection: This favors intermediate trait values, reducing variation. This is contrary to the observed pattern.
Therefore, the correct answer is Disruptive Selection, where individuals with either very short or very long tails have higher fitness compared to those with medium-length tails.
Important Questions from Stabilizing selection
- Male rhinoceros beetles have horns that they use to fight each other. Despite the competitive advantage of having large horns, horn length never exceeds two thirds of their body length. What form of selection explains why horn length is constrained?
The figure below shows how feeding rate varies with age (old/young) and with body size (small/large) in males of a deer species. Based on this figure, which of the statements below is FALSE?
The distributions of beak size in a bird population at two different times are shown below. In going from time $t = 0$ to $t = t_1$, the variance of the distribution in beak size in the population has _________.
