GeneralBiologyOnline

 
 
 
   

General --------Biology -----------------Online------------------___________________________- Chapter 1.  Introduction:  Themes in the  Study of Life---

Having read about natural selection, consider Darwin's two "observations" and his "inference," and apply them to explain how populations of white ptarmigans in Alaska became mostly white, and stayed mostly white, over generation after generation.

Some questions to get you started:

• What might be the major predators of the ptarmigan in Alaska? _________________
• Are you surprised that this same species of ptarmigan is found in Montana, but it has brown feathers that blend in with the dry rocky habitat? ______
• Would you expect the Montana population of brown ptarmigans to produce an occasional white individual?  an occasional dark brown individual? an occasional black individual? ________
• Are individual humans occasionally born as albinos, no skin pigmentation at all? _____
• What might happen in snow covered Alaska to the occasional ptarmigan that is born brown? _____________________________________
• In this snowy environment, which color ptarmigan is most likely to live and reproduce chicks? _____________ (This is an example of the "differential reproductive success" you read about in the text.)
• Since feather color is a genetic trait, what color would most of these chicks be? _____
• Assume global warming is in fact happening; if all the snow in Alaska gradually melts over 10,000 years, then what shifts in ptarmigan feather color would you expect over successive generations? ____________________________________ 
• As more and more snow gradually melts, what color ptarmigan would tend to escape predators more and more efficiently and be more likely to live and reproduce chicks? _________
• Would this shift in feather color occur in 1 generation, or would it take many generations? ______________ 

Assignment:  Once you have thought this topic through, write a 3 to 6 sentence paragraph explaining how the population of white ptarmigans in Alaska could change into a population of brown ptarmigan in response to global warming.  (Hint: I want you to explain what happens in the reproductive process to cause "natural selection" to produce ptarmigan so well "adapted" to their environment.)  Turn your paragraph in by placing it in the Assignment Box as you enter class.