Student Exploration: Rainfall and Bird Beaks
Vocabulary: adaptation, beak depth, directional selection, drought, evolution, natural selection, range, stabilizing selection
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
During the voyage of the HMS Beagle (1831–1836), the young Charles Darwin collected several species of finches from the Galápagos Islands. Two of Darwin’s finches are shown below.
Which species do you think is best adapted to a diet of small, delicate seeds? Explain why you think so.
Which species do you think is best adapted to a diet of large, tough-to-crack seeds? Explain.
Darwin’s finches are one of many types of animals on the Galápagos Islands that have unique adaptations, or traits that help an organism survive in its environment. The Rainfall and Bird Beaks Gizmo™ allows you to explore how rainfall influences the range of beak shapes found in a single finch species.
The beak depth of a finch is the distance from the top of the beak to the bottom, as shown.
What is the current average beak depth in the Gizmo?
Select the HISTOGRAM tab. Do all the finches have the same beak depth?
Click Play () and let the simulation play for five years with average rainfall (25 cm/yr). Select the GRAPH tab and view the Finches vs time and Beak depth vs time graphs.
How does the finch population change?
Does the beak depth change significantly?
Get the Gizmo ready:
Click Reset ().
Introduction: The Galápagos Islands are very dry, with an average rainfall on some islands of only 12 centimeters per year. The amount of rainfall has a large impact on the abundance and types of seeds that are available to be eaten by finches. In the process of natural selection, only the finches that are best adapted to the available seed types survive and have offspring.