Small+populations


 * Loss of Genetic Variability**

You learned about some of the Puritan tiger beetle's physical characteristics during the PowerPoint presentation. These visible traits, and many that you cannot easily see are all stored in the species' genetic pool, the collection of all possible characteristics. When the size of the population shrinks, so does its gene pool, removing possible genetic variation. Over the short-term this loss of variability may not be a problem. However, if a change to the environment occurs, that variation may become critical for individuals to survive. A variation may be resistance to a rare disease, or an unusual condition. If it disappears, the species is at risk of succumbing to the rare condition. One of the goals of the Puritan tiger beetle Recovery Plan is to conserve genetic variability against changing conditions in their environent (36).


 * Genetic Drift**

As you probably have studied, natural selection is the process by which individuals that are well adapted to their environment contribute their genetic characteristics to subsequent generations. Beneficial traits are kept in a population's gene pool. This collection of genes reflects the traits that are most successful at any point in time. Genetic drift is a way for traits that were not selected to remain in the gene pool, they gain prominence by chance. An example is when a population is very small, and the characteristics of the few remaining members are passed on to future generations in high frequency, where the traits would otherwise be rare (36).


 * Inbreeding Depression**

This condition occurs when individuals in a small population lose a healthy mix of traits between parents. If both parents share the same genetic characteristics there is a chance that serious genetic diseases that can only occur when both parents have the same rare genetic trait pass both of them on to their offspring. The result is an increase in genetic diseases among individuals in the population, decreasing the fitness of the population (36).