Darwins Finches Reading by amctavish


									             Darwin’s Finches: an example of Adaptive Radiation

Read the following article and on a separate piece of paper write 10 points that
you did not know before. You will hand this in!

When members of a population undergo evolutionary divergence, new species can
develop from a common ancestor. For this to occur, members of the population must be
reproductively isolated from each other and each group must be exposed to different
pressures. Therefore, different groups of the population adapt to different pressures,
their gene pools diverge (become different) and new species may be produced, each
unable to reproduce successfully with the other. One example of this that we have
already talked about is the Resident & Transient Orcas. The most well known example
of this can be seen in the Galapagos Finches first described by Charles Darwin.

Fourteen species of finches are found on the Galapagos Islands, all have similar
plumage, nest building behaviors and calls, but the different species can be easily
distinguished by the size and shape of their beaks. Five of these species are shown on
the next page. Among the animals Darwin studied were 13 species of finches found
nowhere else on earth.

Adaptive radiation suggests that an ancestral mainland finch populated the islands very
soon after they were formed. With no other species of bird to compete with, finches soon
occupied all island niches. Since ecology varied from island to island, finch populations
evolved slightly different adaptive patterns. In order to reduce competition for food,
finches adapted different feeding habits and evolved different beak structures to match
their food source.

Darwin's finches are an elegant example of 2 important aspects of the evolutionary
process: geographic isolation (isolating mechanism) and adaptive radiation. Over an
extended period of time, geographic isolation allows natural selection to produce new
species. The evolution of distinctive structural adaptations and behavior patterns in a
group of closely related descendant species is called adaptive radiation and is a means
by which organisms respond to competition for resources. Natural selection favors those
individuals whose characteristics are most suited for survival and reproduction for a
particular way of life.

The process described above can occur over and over. In the case of Darwin's finches, it
must have been repeated a number of times forming new species that gradually divided
the available habitats between them.

The formation of a number of diverse species from a single ancestral one is called an
adaptive radiation.

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