In the amazon in 1986, a new species of non-poisonous frog was introduced. In the region, there are two species of snakes, one very large and one very small. These two snake species feed on frogs. Upon introduction into the region, scientists measured the size of the new frog species. In year 2000, the frogs were again measured. The following data was obtained. What kind of selection is this? Why do you think this type of selection was observed?