Selection is the process that increases the frequencies of plant resistance alleles in natural ecosystems through coevolution, and it is the process that increases the frequencies of virulence alleles in agricultural ecosystems during boom and bust cycles. Photo: Ibbiologystudentone via Wikimedia Commons, CC-BY-SA 4.0. Explanation: Directional selection favors a specific trait within some individuals in the population, because they develop greater biological efficiency or have adapted better to environmental … The first type of natural selection is called directional selection. A classic example of this type of selection is the evolution of the peppered moth in eighteenth- and nineteenth-century England. When the environment changes, populations will often undergo directional selection, which selects for phenotypes at one end of the spectrum of existing variation. An example of directional selection is fossil records that show that the size of the black bears in Europe decreased during interglacial periods of the ice ages, but increased during each glacial period. Another example is the beak size in a population of finches. Scientists document, for example, that the acid tolerance of several plant species has increased significantly in the polluted area. Sometimes this is survival of the fittest or the adaptation of organisms that are better suited to the environment in other ways. For the two co-occurring plant species, Heliconia bihai and H. caribaea in the Eastern Caribbean, we evaluated for five populations over 2 years the strength and direction of natural selection on corolla length and number of bracts per inflorescence. Answer: Plant species that have increased their tolerance to acid in the presence of environmental contaminants is an example of a response to directional selection (option e).. Phenotypic matches between plants and their pollinators often are interpreted as examples of reciprocal selection and adaptation. It derives its name from the shape of the approximate bell curve that is produced when all individuals' traits are plotted. A directional selection is a force in nature that causes a population to evolve towards one end of a trait spectrum. Phenotypes are the observable characteristics in a species, and when a population of organisms experiences a change in their phenotype it will generally be subjected to one of the three different types of selection.Directional selection is natural selection that favors … Directional Selection Definition. While some traits are discrete and have specific variations (think eye color), other traits are continuous, and exists as a wide range of nearly infinite values (think height).If a discrete trait goes through a directional selection, only … Selection is a directional process that leads to an increase or a decrease in the frequency of genes or genotypes. Directional Selection. This is an example of A. directional selection. The number of plants of medium height will increase while the numbers of short and tall plants will decrease. Combined, these two selection pressures select to maintain plants of medium height. Examples of Natural Selection Natural selection, a concept first theorized by Charles Darwin , is the adjustment of genes throughout generations based on factors that help living organisms survive. Directional Selection. Instead of the bell curve falling directly in the middle of the axes on which they are plotted, it skews either to the left or the right by varying degrees. 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