GRE Subject Test: Biology : Understanding Community Ecology

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Understanding Community Ecology

 

Which of the following best defines the interspecies interaction in the following situation?

Jackrabbit populations introduced to the Australian outback from Europe in the 1800s decimate communities of desert shrubs and grasses.

Possible Answers:

Mutualism

Predation

Parasitism

Commensalism

Amensalism

Correct answer:

Amensalism

Explanation:

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.

Example Question #2 : Understanding Community Ecology

Hummingbirds use their long beaks to drink nectar from flowers. In turn, they carry the pollen from flower to flower, assisting the reproduction of the flowers.

What relationship does this describe?

Possible Answers:

Resource Partitioning

Parasitism

Co-evolution

Competitive Exclusion

Mutualism

Correct answer:

Mutualism

Explanation:

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.

Example Question #3 : Understanding Community Ecology

When measuring biodiversity, there are several possible indices to use, such as alpha diversity or beta diversity. What does beta diversity, or species evenness, measure?

Possible Answers:

The rate of change in species composition from one habitat to the next

The diversity of the entire geographic area

The number of individuals in a population

The number of individuals per square kilometer

The species richness in a patch of uniform habitat

Correct answer:

The rate of change in species composition from one habitat to the next

Explanation:

Beta diversity measures the rate of change in the species composition of one habitat as compared to others. This is called the species evenness of an area. For instance, if one habitat has radically more species than a neighboring habitat, this would result in a high beta diversity. Alpha diversity is measured as the number of species in a uniform area, and gamma diversity is the species richness in a range of habitats (a mix of alpha and beta).

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