4. The data below illustrate the changes in populations of three animals on an island off the coast of California. Of the three animals, only foxes were native to the island. The fox population was relatively stable, yet small, before humans arrived. Humans colonized the island, bringing pigs with them as livestock. But when humans stopped farming, they released the pigs into the wild, where the pigs were able to reproduce quickly, which attracted golden eagles to the island. Golden eagles need a certain level of prey intake to sustain breeding, and the increased pig population provided this. However, golden eagles do not prey only on pigs, and once they established themselves on the island, they began to find other prey, such as foxes.
a. Explain the trend for each of the population curves shown in the graph. (3 points)
b. Like foxes, skunks are native to the island. Originally, before humans came, the skunk population was fairly stable at about half the size of the fox population. Skunks compete with foxes for many of the same prey, but skunks are not preyed upon by golden eagles. Refine the graph by drawing a curve to show how the population of skunks was likely to be affected by the population changes in the other three animals. Explain your graph. (2 points)
