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Variation within species So far in this unit, you have seen that the stability of an ecosystem relies 18 on the diversity of its communities and species and on the interactions 30 among species. The many different species survive because of the 40 relationships established in this complicated “jigsaw puzzle”. Healthy 48 ecosystems have a great deal of genetic diversity among the species that 60 inhabit them. But biologists have also observed a great deal of variation 72 within a population of a single species. For example, you and your 84 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 108 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 134 important if the environment of the species changes. When the species 145 has a great deal of variation among its individuals, it is more likely that 159 some of the individuals will survive environmental changes. 167 Environmental changes do not necessarily have to involve climatic 176 changes. The introduction of a new predator, the spread of a new 188 disease, the introduction of a toxic substance, or the elimination of a 200 food source are all examples of environmental changes that could 210 affect the survival of a species. In these cases, variability within the 222 species will help the species survive. For example, the fox shown in 234 the infoBIT on page 20 has a dark coat instead of the more common 248 red coat. Its dark coat may make it more conspicuous in fields and 261 woods. But if this fox roams into a new habitat that has many black 275 rocks, its dark coat may blend in better with its surroundings. By 287 blending in better, the fox could pounce on its prey more easily. So 300 variations in coat colour may allow different fox populations to survive 311 in different habitats. How variability helps in survival can also be seen 323 in the growing resistance of certain strains of bacteria to antibiotics. 334 One of the first antibiotics, penicillin, used to be very effective against 346 some forms of bacteria. Today, it is far less effective. Researchers think 358 that the overprescription of antibiotics has allowed bacterial 366 populations with variability to survive the application of antibiotics. 375 A few resistant bacteria are not eliminated by the antibiotic that is 387 administered, and reproduce to produce new generations of resistant 396 bacteria. There is some fear that if this trend continues, resistant strains 408 of bacteria may completely replace current strains and antibiotics will 418 no longer be effective. To avoid this problem, most physicians believe 429 those antibiotics should only be used when absolutely necessary. 438