Evolution of Galapagos Finches

In the Galapagos Islands, a species of finch known as Geospiza magnirostris is found primarily on the island of Santa Cruz, where its main food source is the seeds of the plant Tribulus cistoides. A volcanic eruption on a neighboring island created a land bridge to a previously isolated island, which the finches colonized. This new island has a similar plant, Tribulus terrestris, which produces seeds of slightly different sizes and has a different flowering season. Over time, two distinct populations of Geospiza magnirostris evolved: one that continues to feed on Tribulus cistoides and another that exclusively feeds on Tribulus terrestris. Researchers have noticed that the beak size of the finches has diverged significantly between the two populations. The finches feeding on Tribulus cistoides have retained the ancestral beak size, while those feeding on Tribulus terrestris have developed larger beaks to handle the larger seeds. There is minimal interbreeding between the two populations.