Question

crossbills can prey on lodgepole pines without the interference of squirrels, youre 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).

lets 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 no difference in cone mass based on the predation of crossbills.

(there is a bar graph on the right side with labels like \cone shape (width/length 1.5)\, \cone mass (grams)\, \pine cone trait\ and y - axis values around 7, 7.5, 8.)

Explanation:

To answer, we analyze the graph (even with partial visibility) and ecological principles. When crossbills feed on pine cones, natural selection acts:

• For cone shape: If crossbills' predation favors thicker cones, but shape-wise, "more circular" (wider relative to length, since width/length ratio—if ratio is higher, shape is more circular) and "heavier (more mass)" make sense. The "Cone Shape (Width/Length 1.5)" and "Cone Mass (grams)" bars: green (maybe before) vs gray (after). If gray (after predation) has higher width/length (more circular) and higher mass, then:
• "Pine cones are more circular in shape" (higher width/length means more circular than long/narrow).
• "Pine cones are heavier (have more mass per cone)" (mass bar for gray is taller, so more mass).
• "Pine cones are more long or narrow" is wrong (circular is opposite). "Lighter" is wrong (mass increases). "No difference" is wrong as predation drives trait change.

Answer:

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