Why do populations have different bill sizes when they occur with other species?
When the two species live on different islands they most likely consume similar foods and so their beaks are similar in size. When they occur in the same area, their niches overlap and there would be great competition for the same resources. Under these circumstances, one species would usually outcompete the other driving it to extinction. But what often happens is that selection will favor a splitting up of the resources, called resource partitioning, and under these circumstances, each species may become more “specialized” for its portion of the niche, resulting in different morphologies, called character displacement. FIGURE 54.9 Detecting interspecific competition. This experiment tests how removal of kangaroo rats affects the population size of other rodents. Immediately after kangaroo rats were removed, the number of other rodents increased relative to the enclosures that still contained kangaroo rats. Notice that population sizes (as estimated by number of captures) changed in s
