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Evolutionary Patterns on an Oceanic Island
by Jeanette Cain
An island in the ocean is almost a microcosm of the evolutionary processes. The fundamental genetic processes are the same as those that happen on continents, but the results are often quite different. The beginning point for an origin of island species are the various populations that have reproducing and interbreeding participants. The natural populations will be as varied as the human populations.
So, how can an island, with one single immigrant produce a varied group of offspring? One answer is that islands do not always begin with one immigrant, since a couple capable of mating would be the minimum number needed to reproduce, except for a small number of animals capable of asexual reproduction. For this reason, it is certainly logical to reason that it was not only two that arrived, but rather a flock of individuals. This small flock would represent the first colony.
A gravid female, one that is carrying several eggs would be another possibility. The chance that a potential mother would arrive in a healthy condition is a potentially limiting factor. Should a single individual begin a population, a high variation in the population would seem difficult. A single plant seed or fern spore can begin a colony. Due to genetics, an individual has two sets of chromosomes, thereby carrying two sets of genes that will probably have many differing features.
Should these be scattered by chance by the young, the result will be different individuals. Mendel's self-pollinated pink-flowered pea experiment yielded both white- and red-flowered offspring. As each generation produces more offspring, each will have a chance of producing mutations, since no organism is free from the probability of mutation for too long.
Most of these mutations will be unfavorable, because only a small number can permit a species to enter and live in the new areas, which are a result of the changing in old areas. A wild species is anything, but uniform as stated by Charles Darwin. An example is the number of different breeds of cats that come from a single species.
Another clue for the varied and new types of species may be due to a weedy factor. This weedy animal, or plant, are those capable of mutation and change in a rapid evolutionary sense. Any immigrant offspring born on the island that was incapable of adaptation would probably become extinct in several generations. Any organism with a high mutation rate will be favored on oceanic islands and possibly favored by natural selection.
Any animal and plant that do not have specifics likes and dislikes would do better on an island. Those animals and plants that have a precise, definite set of conditions would make a better immigrant to the island.
Source:
1. Carlquist, Sherwin. Island Life: A Natural History of the Islands of the World." The Natural History Press: Garden City, NY. 1965
Further Study:
Galapagos Islands Natural History
The natural history of the Galapagos Islands has fascinated visitors since their famous guest in 1845. Darwin's observations during his voyage on the HMS Beagle laid the foundation for a theory that impacted western thought --the theory of evolution.
Kokee Natural History Museum
Koke'e Natural History Museum is a little museum with heart open 365 days a year. Koke'e Museum provides interpretive programs and exhibitions about Kaua'i's ecology, geology and climatology.
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