The competitive exclusion principle states that two species cannot occupy the same niche without one of them driving the other extinct. Thus, species either occupy a slightly different niche, or occupy a different physical location from one another, an evolutionary strategy known as niche partitioning. 

Because two species cannot exist within the same niche, if they are to occupy the same geographic space, they must use different resources, or one of them will be driven to extinction. This practice is known as resource partitioning.

Coevolution is a process by which two or more species evolve in response to one another, and generally describes competing species. While the hummingbird and the flower may evolve due to this relationship, coevolution more freqeucntly describes the evolution of defense mechanisms in response to a predator-prey relationship. Parasitism is the relationship in which one species benefits at the expense of the host. This can sometimes lead to coevolution, depending on how the host reacts. Neither species is being harmed in the given scenario, so this is incorrect. Commensalism is when one species benefits, but the other species is not impacted. In this case, both the hummingbird and the flower are benefiting, so this is not our answer. Resource partitioning is when species evolve together to share resources in a sustainable way. The hummingbird is using a resource that the flower provides, but they are not "sharing" in the sense of the definition of resource partitioning. Competitive exclusion describes the phenomenon when two species share the same niche, and the stronger one forces out the weaker competitor. 

Mutualism, the correct answer, describes a relationship wherein species exploit each other mutually. In this case, the hummingbird gains nutrition from the flower, and the flower gains a reproductive advantage from the hummingbird.

Sharks have been shown to be very resistant to infection when they have been wounded. It is also notable how low cancer rates are in sharks—in fact, researchers from MIT have isolated a potential anti-tumor agent in sharks' skeletons that could further cancer research with regard to human patients. 

The over-browsing by the invasive jackrabbit population has resulted in harm being done to the desert plant communities with no negative impact on the rabbits, resulting in amensalism.

Species evenness is a measure of diversity that takes into account the relative proportion of different species in a given area. Richness can also be classified as a measure of diversity; however, it refers to the number of different species in an area rather than proportion. Last, phylogeny refers to the construction of branched models that illustrate evolutionary pathways.

Bottleneck effect occurs after a drastic reduction in population size due to events such as a natural disaster, or widespread disease. The remaining population lacks genetic diversity because there are fewer individuals and fewer genes present within the population. This is the correct answer. The founder effect is not correct because it is defined as the loss of genetic variation as a result of a few numbers of individuals establishing a population. Geographic isolation occurs when a population is isolated from others due to geographic boundaries such as mountains, cliffs, or large bodies of water; therefore, it is not the correct choice. Last, genetic drift refers to the change in frequency of gene variation due to random sampling and does not correctly answer the question.

Parallelism can describe a type of evolution, but does not represent a type of species interaction. On the other had the other choices—interspecific competition, predation, parasitism, and mutualism—are types of species interactions. Interspecific competition occurs when members of species compete for the same resource or niche. Predation happens when one species (predator) feeds on another species (prey). Parasitism takes place when one organism lives off the body of another. This organism is a parasite and usually lives inside or on the host. Mutualism refers to interaction between multiple species for the benefit of all species members.

The question describes a mutualistic relationship in which both the bee and the flower benefit. Mutualistic relationships can be described as win-win interactions between species. Facilitative relationships occur when one species benefits and the other species is not impacted in any way. Competitive relationships are win-lose interactions where one species benefits and the other species is detrimentally impacted. 

The correct answer is genetic drift. This is the only answer choice that refers to random, natural process by which allele frequencies are reduced in general populations. All the other terms are events that occur in response to small population sizes or colonization.