The world famous Galapagos Finches were first brought to scientist's attention when Charles Darwin's voyage to South America ended up in The Galapagos Islands. When he first observed the birds on the separate of the island, they were so different that he assumed they were different birds all together. He then figured out that the 14 different species of Galapagos Finches that inhabit the islands originated from the single species of Mainland Finches that arrived on the islands two to three million years ago. Darwin was also able to formulate his principle of Natural Selection through this observation.
The appearance of the birds changed mainly due to the climate variations between the islands. Lower islands are dryer with rocks covering the surface of the land. On these lower islands, the finches are mainly herbivores. They walk along the ground eating the small seeds and grain that lay within the rocks. Islands with higher elevations have larger trees where carnivorous finches can eat the larva that live inside the branches.
Finches that inhabit the islands with lower elevations are known as ground finches. Over the years they have evolved into three different species of ground finches - the small ground finch, the medium ground finch, and the large ground finch. The small ground finch has a somewhat pointy beak in order to pick up small seeds and grain off of the ground with ease. Throughout the years, the climate experienced many droughts that caused the supply of seed and grain present on the ground to dwindle. Only the seeds with hard pointy shells were able to survive the harsh heat. The small ground finches were unable to crack open the strong exteriors of the seeds and starved as a result. This climate change and the change in food source gave rise to the medium and large ground finches. They had larger and thicker beaks that were able to break through the tough seeds. Natural Selection led to the formation of two new species of finches and allowed them to dominate the islands of lower elevation.
On the islands with higher elevation, many finches either eat the fruit from the cacti along the dryer shorelines or larva from in the trees present inland on the hills. Because the rocky coast is so barren and hot, cacti are the only plants that survive. Finches that live in that area have pointy beaks that allow them to eat the fruit of the cactus without getting stuck by the prickly thorns that cover the plant's surface. Other finches of these islands live in the trees and eat the larva of termites and beetles. These wood pecker finches have thick, sturdy beaks that have the ability to peck through tree branches in order to get to the larva living inside. Variations in the climate on these islands cause a wider variety of food for the finches that live there. This variety is what caused new species of finches to form with their different shaped beaks.
The different finch species are officially recognized when mating between the birds ceases to exist. How do you think this occurs? What possible causes could there be for mating to stop between birds that were once exactly same?
Sources:
Galapagos Finch Evolution
Instant Evolution Seen in Darwin's Finches
DNA Reveals How Darwin's Finches Evolved
No comments:
Post a Comment