Why Do Tropical Birds Lay Fewer Eggs?

Introduction to the Activity

You learned that trade-offs among life history traits are commonly observed in nature. Remember that trade-offs arise when a change in one trait that leads to an increase in fitness is counter-balanced by change in another trait that leads to a decrease in fitness. One of the better-studied life history trade-offs occurs between survival and reproductive investment.

• The following activity provides you with an opportunity to work through a scientific experiment focusing on an evolutionary trade-offs influencing the evolution of clutch size in a bird, the Great Tit (Parus major).
• Begin by visiting this website Virtual Labs and work through the activity by following these steps:
• Read the introductory material available by clicking on ‘Explore the Issue Being Investigated'.
• Read the Abstract and Introduction from the ‘Original Paper'.
• Complete the ‘Virtual Experiment Exploring the Original Paper'.
• Read ‘Gain an Overview of the Experiment'.

Answer the questions below.

• Examine your conclusions from the experiment by answering the following questions:
• According to Lack's hypothesis, natural selection should favor birds that lay 12 egg clutches because they result in more surviving offspring. Do the results of this experiment match the prediction from Lack's hypothesis? Explain.
• A larger percentage of birds in the study population laid 8 - 9 eggs but this resulted in lower survival of the young. What factors might keep the birds from maximizing their reproductive output? (Review the original paper or the "Life Histories" section of your readings.)
• Do your results support or reject your hypothesis? Explain.