Final answer:
The changes in flower length and the hummingbird's beak length an examples of coevolution, a process where species mutually influence each other's evolution. If the hummingbird species went extinct, flower pollination might decrease, leading to a possible decline in the plant population. This interaction supports the Red Queen Hypothesis, which emphasizes the need for constant adaptation to survive.
Step-by-step explanation:
The occurrence where a species of plant with red, tubular flowers has changed over time to have longer flowers and a species of hummingbird has also changed to have longer beaks to access the nectar is best described by the term coevolution. Coevolution is the process in which two or more species reciprocally affect each other's evolution through natural selection. An example of this in nature is seen with certain flowers and their pollinators, such as the trumpet creeper flower and the hummingbird, where the flower has evolved to be tubular and attract its specific pollinator, and the hummingbird, in turn, has evolved a long and narrow beak to access the nectar deep within these flowers.
If the hummingbird species went extinct, it might have a significant impact on the flower species. Since only that specific species of bird can reach the nectar, the flowers would not get pollinated, resulting in a decrease in the plant's ability to reproduce and potentially leading to a decline in the plant population.
The scenario that provides the best support for the Red Queen Hypothesis, which posits that species must continually evolve to maintain their existence against ever-evolving opposing species, is 'b'. Individuals of a snail population that reproduce asexually die out after a parasite invades its territory because they lack the genetic variation offered by sexual reproduction to compete against the parasite.