Question

now that you’ve found a location where crossbills can prey on lodgepole pines without the interference of squirrels, you’re now ready to see if a long - term interaction between these two species can cause a change in the traits of their populations. this can occur in two ways:

• the crossbills can cause trait changes in the pine population (such as developing thicker cones) or
• the pine trees can cause trait changes to emerge in the birds (such as developing thicker beaks).

let’s start by focusing on whether the pressure of crossbill predation causes the pine trees to change their traits.
what differences do you notice in the pinecones in areas where only crossbills are feeding on pine cones? after crossbill predation...
check all that apply.

• ✔️ pine cones are more circular in shape.
• ☐ pine cones are more long or narrow in shape.
• ✔️ pine cones are heavier (have more mass per cone)
• ☐ pine cones are lighter (have less mass per cone)
• ☐ there is no difference in cone shape based on the predation of crossbills

(there is a bar graph on the right with “before crossbill predation” (green) and “after crossbill predation” (gray) for “cone shape (width/length*15)” and “cone mass (grams)”)

Explanation:

To determine the correct options, we analyze the bar graph and the question context. For "Cone Shape (Width/Length*15)", the gray bar (after predation) is lower than the green bar (before), but the description "more circular" relates to a higher width - to - length ratio (since circular would have a more balanced width and length, increasing the ratio). For "Cone Mass (grams)", the gray bar (after) is higher than the green bar (before), so mass increases. So "Pine cones are more circular in shape" and "Pine cones are heavier (have more mass per cone)" are correct. The other options are incorrect: "more long or narrow" would decrease the width - length ratio, "lighter" contradicts the mass graph, and "no difference" is wrong as the graph shows differences.

Answer:

• Pine cones are more circular in shape.
• Pine cones are heavier (have more mass per cone).