Question

Researchers discovered that in a certain population of songbirds, the birds with medium-sized wings were favored to survive severe storms (storms with high winds) than those which had either longer or shorter wings. If the region where the birds live is subject to frequent severe storms, what would you predict is occurring in the songbird population?

• A. Bottleneck effect
• B. Founder effect
• C. Disruptive selection
• D. Stabilizing selection
• E. Directional selection

Answer 1

Answer: (A)

Bottleneck effect

A. Even if organisms do not move from place to place, yet occasionally their populations may drastically reduce in size. This may occur due to flooding, drought or any other change in environment. The few surviving individuals may constitute a random genetic sample of the original population. This resultant alterations and loss of genetic variability is called bottleneck effect.

B. Sometimes, one or a few individuals disperse and become the founder of a new, isolated population at some distance from their place of origin. These pioneers are not likely to have all the alleles present in the source population. Thus, some alleles may be lost from the new population and others may change drastically in frequency. This is called the founder effect.

C. Disruptive selection occurs where an environmental change may produce selection pressure that favours two extreme characteristics. For example, grass plant on welsh copper mines. Contaminated soil containing copper is lethal to normal grass plants but a chance mutation allowed one plant to grow. This plant prospered and reproduced but only on the contaminated soil. On normal soil, it grew more slowly than normal plants and was easily out-competed.

D. Stabilizing selection occurs when the environment does not change. Natural selection has to produce change and if an environment does not change there is no pressure for well-adapted species to change. Fossil evidences suggest that many species remain unchanged for long periods of geological time.

E. Directional selection occurs whenever the environment changes in a particular way and therefore, is a selective pressure for species to change in response to the environmental change. For example industrial melanism. Industrial melanism is a phenomenon shown by light coloured peppered moth (Biston betularia typica) and dark coloured moth (Biston betularia carbonaria). It is an evolutionary process in which darker individuals predominate over lighter individuals since the industrial revolution is a result of natural selection.

Hence if the birds with long wings survived the storms and dominated in the area, then this would be considered as Bottleneck effect.

So, the correct answer is 'Bottleneck effect'.