A flock of migrating birds is blown off course by a storm and carried towards a small island that has no birds. Only three of the birds survive the storm and make it to the island. They start to reproduce and, after several years there are 500 birds on the island. Does the genetic variation in this population of birds results from a population bottleneck or founder effect? Explain.
2) Explain how genetic drift can lead to a reduction in the genetic variation within a population.
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To determine whether the genetic variation in the population of birds resulted from a population bottleneck or founder effect, let's first understand what each of these terms means:
1. Population bottleneck: A population bottleneck occurs when a severe reduction in population size takes place and only a small number of individuals survive. This event can lead to a loss of genetic diversity since the surviving individuals represent only a subset of the original gene pool.
2. Founder effect: A founder effect occurs when a small group of individuals colonizes a new geographic area or habitat, resulting in a new population. Since this founding population is typically small, it carries only a fraction of the genetic diversity present in the original population, leading to reduced genetic variation in the new population.
In the given scenario, three surviving birds made it to the small island and started the population. This indicates a founder effect rather than a population bottleneck, as only a small group of individuals founded the new population.
Furthermore, if the birds on the island have a reduced genetic variation, this would support the idea of a founder effect. The original population likely had more diverse genetic characteristics, but the limited number of founding individuals on the island gave rise to a smaller gene pool during population establishment. Consequently, the genetic makeup of the resulting population exhibits reduced variation compared to the original population.
It is important to note that while both population bottlenecks and founder effects can result in reduced genetic diversity, the key distinction lies in the cause. A population bottleneck is caused by a sudden and drastic reduction in population size, while a founder effect arises from the establishment of a new population by a small group of individuals.