Final answer:
The competitive exclusion principle posits that no two species can coexist in the same niche by competing for identical resources. Species can adapt via character displacement or adopt different niches to avoid direct competition, affecting their evolution through natural selection.
Step-by-step explanation:
The competitive exclusion principle is a concept in ecology that dictates no two species can coexist while competing for identical resources within the same habitat at the same time. This principle suggests that the species less adept at using these resources will need to adapt, move to a new area, or face extinction. An example of such adaptation is character displacement, where competing species evolve different traits to utilize varying resources, diminishing direct competition. This adaptation can be observed in the varied beak sizes and shapes of Darwin's Finches, which allow them to exploit different types of food in the same environment, thus reducing overlap in resource use.
Species can also coexist by specializing in different niches within the same habitat, which involves unique adaptations and behaviors that lessen competition for resources. An example demonstrating this principle involves two protozoan species, Paramecium aurelia and Paramecium caudatum, where P. aurelia outcompetes P. caudatum for food when placed together, leading to the extinction of the latter. This principle plays a significant role in evolution through natural selection, where advantageous traits that reduce competition are favored over time.