Coevolution Pinterest

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Some Central American Acacia species have hollow thorns and pores at the bases of their leaves that secrete nectar (see image at right). These hollow thorns are the exclusive nest-site of some species of ant that drink the nectar. But the ants are not just taking advantage of the plant—they also defend their acacia plant against herbivores.  the plants would not have evolved hollow thorns or nectar pores unless their evolution had been affected by the ants, and the ants would not have evolved herbivore defense behaviors unless their evolution had been affected by the plants.

Nature

The evolution of long bills and sickle-shaped bills in some Latin American hummingbirds matches the long or sharply curved flowers so that they can sip nectar (and pollinate).

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Birds have deeper, less curved bills in places where the pinecones have thick scales,than where the pinecones have thin scales. 

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In most of the Rocky Mountains, red squirrels are an important predator of lodgepole pine seeds. They harvest pinecones from the trees and store them through the winter. However, the pine trees are not defenseless: squirrels have a difficult time with wide pinecones that weigh a lot but have fewer seeds.

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Where squirrels are the main seed predator, trees should have stronger defenses against squirrel predation, and where birds are the main seed predator, trees should have stronger defenses against bird predation. This turns out to be true. Where there are squirrels, the pinecones are heavier with fewer seeds, but have thinner scales, like the pinecone on the left. Where there are only crossbills, pinecones are lighter with more seeds, but have thick scales, like the one on the right.