Question

case study
effects of changing pine cones on
crossbills
have the crossbills changed in reaction to the
changes in the pine tree’s cones?

has the crossbill population changed as a
result of the pine cones adapting structures
to protect against them? look at the graph.
how does the bill depth of the crossbills
change when crossbills are the main
predator in areas where the pine trees have
adapted structures to keep birds away?

what adaptation have the
crossbill populations developed
in reaction to the changes in
pinecones?

• crossbills have developed beaks with

smaller depth in areas where pine cones
have adapted structures against them.

• crossbills have developed beaks with

greater depth in areas where pine cones
have adapted cones against them.

• crossbill beak depth is not affected by

whether or not pine trees have adapted
their cones against them.

• crossbill survival does not depend on their

beak depth and hence, their population has
made no adaptations.

graph (y-axis: estimated relative survival; x-axis: bill depth (mm)) with legend:
1 = survival, 0 = death;
green graph= optimal crossbill beak
sizes in areas where pine trees have
adapted to bird predation;
purple graph= optimal crossbill beak
sizes in areas where pine trees have
not adapted to bird predation

Explanation:

To determine the adaptation, we analyze the graphs. The purple graph (pine trees not adapted) has an optimal beak depth around 9.5 mm, while the green graph (pine trees adapted) has an optimal beak depth around 10.0 - 10.5 mm. This shows that in areas where pine cones adapted (to keep birds away), crossbills developed beaks with greater depth to access seeds, as a deeper beak would help them handle the adapted pine cones. The first option says smaller depth (incorrect), the third says no effect (incorrect), the fourth says no adaptation (incorrect). Only the second option matches the graph - based analysis.

Answer:

B. Crossbills have developed beaks with greater depth in areas where pine cones have adapted cones against them.