A species of seagull migrates into the region in which a crab population lives. This...
A species of seagull migrates into the region in which a crab population lives. This type of seagull has never lived in this particular environment before. The seagulls eat crabs, and begin to prey on the crab population. The smallest of the crabs are able to successfully hide under rocks and avoid being eaten by the seagulls. The largest of the crabs are too big to fit inside of the seagulls' beaks, so the seagulls learn not to try to eat them. Over time, the seagulls prey on the medium sized crabs, and only the smallest and largest members of the initial crab population survive. Which type of selection does the described situation model?
- A. Convergent selection
- B. Directional selection
- C. Random selection
- D. Disruptive selection
Correct Answer: D. Disruptive selection
Explanation
The situation presents an example of disruptive selection. In disruptive selection, organisms with an intermediate phenotype are selected against. This means that individuals with the intermediate phenotype will decrease in prevalence in the population, while organisms on either end of the phenotype spectrum will increase in prevalence. In this case, the trait being discussed is crab size. The smallest and largest crabs survive, but those with an intermediate (middle-sized) phenotype are eaten.
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