Answers to Analyzing Data 7.1 Questions

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2. No. To see why, we can calculate how many eggs (on average) birds produced over the four years.

3. Yes. On a year-to-year basis, early breeders produced fewer eggs each year in years 2, 3, and 4 than did late breeders. This suggests that allocating resources to reproducing in their first year can reduce an individual's potential for reproducing in years 2-4.

4. Factors other than whether a bird reproduced in its first year may influence its reproductive success in years 2-4. An experimental approach to control for such factors would assign birds at random to the different treatments used in the experiment. There are several ways to test whether females experience a cost to reproduction that reduces their potential for future reproduction. For example, females could be assigned at random to one of the following three treatments: a control in which the number of eggs they laid was not altered; an experimental treatment in which extra eggs were added to their nest (increasing the female's costs of caring for eggs laid); and a second experimental treatment in which eggs were removed from the nest (reducing the female's costs).