105LabManualPredatorPreyNew.pdf - Predator-Prey Coevolution Living organisms within a community interact in a variety of ways The primary relationship

105LabManualPredatorPreyNew.pdf - Predator-Prey Coevolution...

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Predator-Prey Coevolution Living organisms within a community interact in a variety of ways. The primary relationship between predator and prey is a familiar one. The predator organism finds the prey organism and uses it as a source of nutrition. It is quite obvious that this relationship is beneficial for the predator and deleterious for the prey. Through the process of evolution, a prey population with sufficient species diversity can, over time, change with respect to being preyed upon. Some of the organisms within the population may display characteristics that decrease their chance of being eaten. These characteristics confer a reproductive advantage , the individuals survive, reproduce and have a greater number of offspring that exhibit these positive characteristics. Other organisms may display negative characteristics that result in a greater chance of being preyed upon. Their traits will decrease within the population as these organisms fail to reproduce and pass on their traits. Through the process of natural selection these individuals are said to be selected against . Those with positive traits will become more common in future populations. Individuals within a species that have slightly different visible characteristics, or phenotypes , are called morphs . The genetic variation present is not significant enough to qualify the individuals as being different species. The existence of morphs merely reflects the overall genetic diversity within a species. Many forces within nature act upon the predator population that are not directly related to predation but affect survival and reproductive fitness nonetheless. Individuals that are well-equipped to escape from predators may succumb to disease while enough of those that are good prey (at least to the predator) may survive to reproduce and pass on their genes. Because these natural forces change from year to year, the characteristics of individuals within a population varies over time. Traits that are reproductively advantageous one year may be deleterious the next. As a result, a great degree of genetic diversity is maintained within a species over time. This diversity enables a species to survive totally unexpected changes in the environment. Contrary to popular opinion, an alteration in the environment does not cause a change in an individual's genes. Rather it affects the entire population by allowing only those with an already different genetic pattern to survive. The peppered moth ( Biston betularia ) provides one of the best known examples of morph success in varying environments. Prior to the industrial revolution in Britain, the peppered moth existed primarily in its light morph. These individuals were nearly invisible on the light lichen-covered trees on which they rested. A dark morph of the peppered moth existed, but individuals were rare as they were easy targets for birds. Surprisingly, the gene for dark coloration is dominant over the light gene. As industry increased, the tree trunks became darkened and the lichens were killed by the pollutants.
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