Evolution
Overview
Evolution is the process where species diverge in terms of genetic makeup in a population, even to become a new species.
Islands are glasshouses where evolution can occur. They tend to be geographically remote, and thus isolated from outside interference. The Galapagos Islands are no exception, their distance from the mainland being 1,000 km. Each island in the group has varied conditions, which has lead to different common traits being expressed in the populations upon each island.
A population is a group of animals which are separate from another population. The [separate] groups of animals on each of the galapagos islands are examples of different populations. Sometimes two or more populations change enough that they cannot reproduce. This is now an example of two different species.
These changes are caused by a number of means – natural selection, genetic drift and gene flow. Natural selection is the process where members in a population with advantageous characteristics (to their survival) carry on those to future generations, and where those who dont, do not. When two geographically separate populations are exposed to different sets of conditions, they tend to develop in different directions – divergence. Sometimes two separate species develop characteristics which are similar (eg: the flippers turtles and penguins), this is convergence. Convergence usually occurs when the two species share an environment.
An environment is a place where things live. Each of the Galapagos islands is a separate environment. Indeed, an island may contain more than one environment. For example, the beach shore, the lush slopes of a volcano and then the barren crater of that volcano.
The Galapagos Finches
The Galapagos Island's finches are the quintessential example used for evolution. Across the islands, there are around 13 or so different species. It is thought that the ancestors of these finch species were blown off course from mainland South America. In their comparative isolation and varying conditions, they evolved to where they are now. Even today, the populations dynamically change due to enviromental phenomena, like El Nino.
Of the 13 different species, there are 5 "types" – ground finch, cactus finch, tree finch, vegetarian finch, woodpecker finch and the warbler finch. There are several "variations" of the ground finch, cactus finch and the tree finch. They physically vary in body size, head size, beak size, plumage and tail. These types also possess different behaviors as they have adapted to their various environments.
Peter and Rosemary Grant have been researching the finches on Daphane island for the past 15 years. In 1977 there was an intense period of drought. Food supplies for the finches on the island became more and more scarce. The only reliable source of food was cactus and nuts. Only the finches with larger beaks were capable of eating these foods. By the end of the drought, most of the finch population was wiped out. Unsurpisingly, the finches which could eat (the ones with larger beaks) survived more than the ones with smaller beaks. Thus this feature (larger beaks) was more prevalant in future generations of finches. This is a prime exmaple of evolution in action where environmental changes have influenced the physical structures of the finches.
The vampire finches are another interesting example of evolution. They have come to depend on the blood and bodily material of the other residents of their island. Their beaks are more pointed and sharp compared to other members of the Ground Finch family. This helps them draw blood, and get access to hard to reach places like under the plumage of birds. Interestingly, there is also an example of co-evolution between the boobies and the vampire finches. The boobies allow the finches to take care of their parasites (and sometimes a sip of blood). In return, the finches gain a viable food source especially in times of drought. An interesting behavior of the vampire finch is that it possess the ability to eat eggs, by cracking them because they are not strong enough to use their beaks. This behavior is present in no other finch species and is quite unique. This behavioral and physiological changes (from other ground finches) is another example of evolution, as they have apapted to being around lots of other birds.
The woodpecker finch has a most amazing behavior. It uses its beak as a type of sonar to sound out the hollow spaces in tree trunks (where grubs live). Once it thinks it has found a grub, it strips back the bark to expose an opening (to allow access to the grub). If it can reach the grub, then it will. If it can't however, the woodpecker finch utilises a thin stick as a tool to spear the grub (then eat it). This is unique behavior which is advantageous to the population, and thus has been caried forward.