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A hypothetical species of antelope is host to a pathogenic species of bacteria that is spread through the air over short distances of 10 to 20 feet. Scientists have observed that in areas with a low population density, bacteria displaying lower virulence make up a greater presence than virulent strains. While in areas with a high population density, the reverse is true. Below is a graph showing the virulence of the bacterial pathogen compared to the density of the antelope population.

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Which of the following BEST explains the relationship shown in the graph?


In antelope populations with low density, less virulent strains of the bacteria are more successful because infected organisms stay healthy enough to move and spread the bacteria.


In antelope populations with low density, the population of pathogenic bacteria is lower, so fewer antelope are infected and die.


As the population of antelope increases, the pathogenic bacteria become stronger because they have more food.


As the population of antelope increases, the population becomes resistant to the bacteria via natural selection and the bacteria co-evolve to become more virulent.

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