Download Variation Within Species

Variation within species
So far in this unit, you have seen that the stability of an ecosystem relies
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on the diversity of its communities and species and on the interactions
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among species. The many different species survive because of the
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relationships established in this complicated “jigsaw puzzle”. Healthy
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ecosystems have a great deal of genetic diversity among the species that
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inhabit them. But biologists have also observed a great deal of variation
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within a population of a single species. For example, you and your
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classmates are all members of the same species, Homo sapiens, but each 96
of you differs slightly in appearance. Some may have black hair, others
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blonde; some may be tall, others less tall. This kind of variation is seen in 123
all species. Variation within a species is called variability. Variability is
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important if the environment of the species changes. When the species
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has a great deal of variation among its individuals, it is more likely that
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some of the individuals will survive environmental changes.
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Environmental changes do not necessarily have to involve climatic
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changes. The introduction of a new predator, the spread of a new
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disease, the introduction of a toxic substance, or the elimination of a
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food source are all examples of environmental changes that could
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affect the survival of a species. In these cases, variability within the
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species will help the species survive. For example, the fox shown in
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the infoBIT on page 20 has a dark coat instead of the more common
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red coat. Its dark coat may make it more conspicuous in fields and
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woods. But if this fox roams into a new habitat that has many black
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rocks, its dark coat may blend in better with its surroundings. By
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blending in better, the fox could pounce on its prey more easily. So
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variations in coat colour may allow different fox populations to survive
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in different habitats. How variability helps in survival can also be seen
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in the growing resistance of certain strains of bacteria to antibiotics.
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One of the first antibiotics, penicillin, used to be very effective against
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some forms of bacteria. Today, it is far less effective. Researchers think
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that the overprescription of antibiotics has allowed bacterial
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populations with variability to survive the application of antibiotics.
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A few resistant bacteria are not eliminated by the antibiotic that is
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administered, and reproduce to produce new generations of resistant
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bacteria. There is some fear that if this trend continues, resistant strains 408
of bacteria may completely replace current strains and antibiotics will
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no longer be effective. To avoid this problem, most physicians believe
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those antibiotics should only be used when absolutely necessary.
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