Island Beetle Natural Selection…. –Imagine an island where there is an abundance of green algae and a population of green and brown beetles. These beetles are competing for food and space. The green beetles thrive because they are camouflaged to blend in with the algae so birds don’t eat them. The brown beetles live in cracks on the rocks but must come out to eat the algae. They are more likely to be preyed upon by the birds………

The brown beetle population is reduced because they are preyed upon by the birds (selected against). Over time, there are more green beetles in the population than brown beetles. Why? The allele for green coloration has provided a positive adaptation that is favorable in the population. This allele is passed down from generation to generation. Thus, the green phenotype is more common in the population. While the allele for brown coloration is rarely seen in the population because those beetles have a lower survival rate (lower fitness level).

–Pollution caused the algae to slowly dye back and turn a brownish color over 50 years, now the green beetles are easier for birds to spot (and hence, eat). What happened to the population of beetles?……... Environmental Change

Over the 50 years, the allele for Brown color becomes the favored genotype in the population (how?) The green beetles were now selected against (preyed upon because they stood out). The brown beetles thrived and the allele for brown coloration was passed down to each generation. The brown coloration was the adaptation that helped them survive over the 50 years.

Result: Brown beetles become more common in the population than the green beetles. Over consecutive generations, the population mainly contains the brown beetles. These brown beetles now have a high fitness level. They are successful in survival and reproduction. This is Evolution!!!!!! –driven by pollution

Natural Selection Island Example Questions: Directions: Answer the following questions on YOUR OWN PAPER and in COMPLETE SENTENCES. 1. What are the island beetles competing for? What else might they be competing for that is not in the story? 2.Describe the green beetles and brown beetle populations. 3.Define Fitness. 4.Which beetles have a higher fitness level? Why? 5.Which beetles have a lower fitness level? Why? 6.Define natural selection.

7. Which phenotype was favored in this island environment? 8. Which phenotype was selected against? 9. What happened over 50 years? 10. Which allele now becomes the most dominant in the population? Why? 11. Which beetles now have the higher fitness level? Which beetles now have the lower fitness level? 12. What does it mean to have a high fitness level? 13. Define evolution. 14. Define adaptation.