I’m traveling in the Galapagos currently. Hopefully I’m having fun and seeing great birds and other species! In the meantime here’s a little of what I will hopefully be seeing!
The Galapagos’s Natural and Unnatural History: Adaptive Radiation
When we left off, selection was beginning to act on our small band of finches. At first there was one: one group, on one island. They succeeded. Their meager group grew and they established a sustainable population. The population continued evolving with those individuals who were better at getting food and mates in this new land disproportionately contributing to the gene pool. Given enough time, this group will diverge enough so that should it encounter the original population, they would not recognize each other as the same species.
Time continues, as it does. Eventually, some individuals brave the oceans, either intentionally or not, and reach a new island. While this island is not 600 miles away and may only be 1/10th of that distance, it is an effective barrier. Once again, the founder’s effect repeats itself. These birds change in new ways from their original population. And so the story goes.
In some cases, a very divergent group of finches might venture to an already colonized island. Then, three things might happen. They are in direct competition and one group perishes (most likely the arrivals due to number). They are similar enough that they are the same species and they blend their gene pools. They are different enough they occupy different niches and are not in competition with each other.
For Darwin’s finches, this occurred 13 times. There are 13 different species of finches in the Galapagos, so diverse in the niches they evolved to fulfill that Darwin didn’t realize they were all finches. There are other types of birds that have reached the Galapagos. Some are endemic meaning, they are only found there; others are widespread. Endemics include the Galapagos Finches and the Galapagos Penguins (can’t forget those!) while the others include some familiar faces to the readership such as the Barn Owl, Vermillion Flycatcher, Great Blue Heron, and Yellow Warbler.
The Mockingbirds of the Galapagos share a similar pattern of adaptive radiation though not nearly as radiant. The finches are special. Their plasticity has allowed them to fulfill niches on the islands that are typically filled by other families of birds: Woodpecker and Warblers spring to mind as one views the phylogenetic tree below.
No wonder Darwin was so perplexed and we continue to puzzle over the story 178 years later.