Exaggerated traits and breeding success in widowbirds answer key

Florida State College at Jacksonville

BSC1005: Life in its Biological Environment

Science Assessment Artifact 2: Exaggerated Traits and Breeding Success in Widowbirds

The Study Species

Widowbirds are small, finch-like birds and inhabit the grasslands and shrubby savannas of southern and eastern Africa. This group is noted for the pronounced sexual dimorphism (physical differences between males and females). During the breeding season, males grow elaborately long tail feathers that can be up to half a meter in length.

During the breeding season, males secure and defend a territory from other males where they then build multiple nest frames. Males then perform a flight display that has a “bouncy rowing” appearance with loops and exaggerated wing beats to attract females to their territory. Females choose a male for breeding, line a nest frame in his territory with fine grass, and then incubate the eggs and feed the nestlings in that frame.

Natural selection is a process that occurs when some members of a population display an inherited trait and others do not. And if that trait gives the individuals who possess it some type of reproductive advantage over those who don’t (in other words, individuals with the trait produce more offspring that those that don’t have it), then the trait will appear more frequently in subsequent generations. Biologists believe that this process of natural selection has been the primary force in the evolution of species through the history of life, and that it continues to be an important force in shaping traits in species today.

A group of researchers believed that the length of the tails in the male widowbirds is being affected by natural selection. To verify this idea, they would have to show that tail-length made a difference in the breeding and reproductive success of male widowbirds.

Tail Length Study

In an initial field study, researchers compared the number of active nests (nests occupied by female widowbirds) among males with different tail lengths. Results of the study are shown below.

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Questions

1. What conclusion can be drawn from this experiment?

2. What was the question (or problem) addressed in this experiment?

3. What was the experiment's hypothesis?

4. Was the experimenters' hypothesis supported or rejected? Explain.

5. What patterns are suggested by the data with regards to the scientific question addressed in this experiment?

6. Discuss how your analysis of the experimenter's results support or reject the experimenter's hypothesis.

7. What, if any, were the researcher's assumptions?

male tail length (mm)