The first paragraph introduces a claim - "that the overall number of species" increases as you move from the earth's poles (north or south) to the equator (center line). This is referred to as a "latitudinal gradient," and you are told that it's probably "even more pronounced" than we can currently appreciate, because there are a lot of undiscovered species in the tropics (i.e., near the equator).
The next four paragraphs each present one hypothesis for this phenomenon. Paragraph 2 describes "the time theory" hypothesis (#1). Paragraph 3 describes "the species-energy hypothesis" (#2). Paragraph 4 describes a hypothesis that "centers on the tropics' climatic stability" (#3). Paragraph 5 describes what the author of the passage views as the "most plausible hypothesis," which "focuses on regional speciation." (#4).
And then the last paragraph builds on the immediately preceding graph, explaining in greater detail "the mechanism for this rate-of-speciation hypothesis."
This particular question asks you to identify a situation that is "most consistent" with the "species-energy hypothesis" described in the passage. So, go back to the relevant paragraph (paragraph 3) and re-read it if necessary before assessing the answer choices. The hypothesis "proposes . . . positive correlations" between (1) energy from the Sun and rates of growth and reproduction, and (2) rates of growth and reproduction with the amount of biomass, and (3) the amount of biomass with the number of species. See Lines 16-22.
Accordingly, (E) is the answer choice that describes a situation most consistent with this hypothesis. In the arctic tundra, there is less solar energy, which means slower growth and reproduction (because the species-energy hypothesis posits that there is a positive correlation between these things).
