Apex predators are known to influence the trophic network of the environment in which they act. One good example of this is the case of the local extinction and further reintroduction of wolves in Yellowstone Park. Wolves are native to North-America and are known to hunt large prey, such as elk, deer, and even bison. The presence of a wolf pack in an area offers new opportunities for other species. For example, a fresh wolf kill can attract crows, magpies, and even bears, offering the possibility to access food resources they would not be able to hunt by themselves. But not all species benefit from the presence of wolves. For instance, coyotes that can hunt very similar prey as wolves, are usually outcompeted by the larger and more aggressive wolf packs. As a result, in the presence of wolves, coyotes are kept in lower frequencies in the environment. This process sometimes called “mesopredator suppression” predicts that if an apex predator is led to local extinction, then their smaller competitors (mesopredators), could take their ecological role. This prediction was corroborated when wolves were extinct from the Yellowstone Park in the early 1900s. After that, coyotes started not only to increase in numbers, but they also started to congregate in packs, and act cooperatively to bring down large game just like wolves do.

With the reintroduction of wolves in Yellowstone Park in the 1990s, however, coyotes started to decrease in numbers and reverted to their solitary lifestyle. This supposedly happened because even though larger groups can provide increased benefits in terms of caloric intake (packs can bring down prey that is larger than what any individual could do), in the presence of wolves, all large game is taken by that species, leaving coyotes to eat smaller prey and to scavenge, which has a lower caloric reward.

Short Answer Question: With that in mind, choose from the following graphs, which one would represent the relationship between costs and benefits of different group sizes in Yellowstone coyotes both for the period with wolves and without them. Justify your choices.

A B Cnw Cw B B Calories Calories Cw Com 5 1 2 3 4 Pack size 1 2 3 4 Pack size 5 6 C D Bw Bnw Calories Calories С .C Bnw Bw 1

Graph description: Figure 1- Purple lines are benefit curves and green lines are cost curves. C- cost, when costs are the same both with and without wolves; Cnw- cost with no wolves; Cw- cost with wolves; B- benefits, when benefits are the same both with and without wolves; Bnw- benefits with no wolves; Bw- benefits with wolves. Cost curves increase linearly with pack size because it is the cost of sharing food with other individuals in the group.

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