Figure 7.7 Evolution by the bottleneck effect. (a) The greater prairie chicken population in Illinois declined from approximately 12 million in the 1860s to 72 birds in 1990. (b) Averaged across six different genes, the mean number of alleles is high for birds in neighboring states that still have large populations and for the larger, historic population in Illinois that existed in the 1930s and 1960s. In the current population in Illinois, however, the small population is experiencing a population bottleneck and has a lower mean number of alleles. Error bars are standard errors.

Data from J. L. Bouzat et al., The ghost of genetic diversity past: Historical DNA analysis of the greater prairie chicken, American Naturalist 152 (1998): 1–6.