Reading Passage Question:
Of the many organisms found in marine ecosystems, sea otters play a uniquely significant role in maintaining their environments. Sea otters (Enhydra lutris) are a keystone species, a species whose effect on their environment is disproportionately great relative to their size in numbers or weight. Keystone species keep the growth of populations of other species in check and are thereby a determining factor of the type and number of other species in a community; keystone species are so named because their role is analogous to that of a keystone in an arch: while keystones bear the least amount of pressure among the components of an arch, the arch collapses without them.
The sea otter's reputation as a keystone species is largely a consequence of its affinity for sea urchins. Sea otters are known to prey upon over 100 different species, but the bulk of their diet consists of sea urchins and other marine invertebrates. Sea urchins are such highly preferred prey that sea otters have been known to significantly deplete urchin populations. In marine ecosystems at equilibrium, however, sea otters are often the primary force that keeps populations of sea urchins in check. Without sea otters, sea urchins and other seafloor herbivores would graze on help holdfasts, causing kelp to drift away from their substrates and die. The aggregate result of many such events leads to the destruction of entire kelp beds, resulting in a loss of habitat and nutrients for other organisms in the ecosystem. The extended consequences include local extinction of other species and vast urchin barrens: subtidal areas where the unchecked population growth of sea urchins has caused a dearth of kelp and, therefore, other marine species.
This ecological cascade effect of secondary extinctions resulting from a decrease in otter populations and corresponding growth in urchin populations was observed throughout the 19th century along the Pacific coast of North America. Sea otters had been aggressively hunted for their rich pelts since before the 1600s, and this practice was not outlawed until an international treaty was signed in 1911 to prevent further exploitation. Prior to the enforcement of the treaty, hunters caused sea otter populations to decline; this in turn caused sea urchin populations to explode. Consequently, the urchin populations overexploited their primary food source, kelp, creating a preponderance of urchin barrens.
‘Of the many organisms found in marine ecosystems, sea otters play a un’ is a GMAT reading comprehension passage with answers. Candidates need a strong knowledge of English GMAT reading comprehension.
This GMAT Reading Comprehension consists of 7 comprehension questions.
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Questions and Solutions
(A) disdainful
(B) dispassionate
(C) concerned
(D) critical
(E) jovial
Answer: B
Explanation: Please read lines 20–22 in the second paragraph. If sea otters weren't around, sea urchins and other herbivores that live on the seafloor would nibble on kelp holdfasts. Causing the kelp to become detached from its substrate and eventually perish. These lines did not support options A, C, D, and E. Only Option B is a viable choice.
(A) The Sea Otter and the Sea Urchin
(B) Ecological Cascade Effects in Global Ecosystems
(C) Marine Holdfasts: The Key to Biodiversity
(D) A Study of Urchin Barrens
(E) The Sea Otter as a Keystone Species
Answer: E
Explanation: The first paragraph defines keystone species to emphasise the sea otter's relevance in its environment. E is correct since "The Sea Otter as a Keystone Species" summarises the section. Answer choice A is wrong since the otter's impact on kelp beds and other ecosystem elements reduces the sea urchin's significance. D is inaccurate because it doesn't mention the otter, which is important because of the urchins. Choices B and C are overly wide because this paragraph is about the sea otter, not complete ecological concerns.
(A) advocate a strategy for keeping sea urchins in check.
(B) explain the absence of kelp in the North American Pacific coast.
(C) outline the dietary habits of sea otters.
(D) describe the significance of sea otters in their ecosystems.
(E) define the term "keystone species."
Answer: D
Explanation: The first paragraph introduces sea otters and outlines their position as keystone species. The second paragraph describes their impact on two populations, and the third paragraph shows their impact on human culture. Thus, the chapter as a whole explains the sea otter's significance, which is answer choice D.
(A) organisms that dwell at the lowest level of a body of water
(B) a root-like structure that anchors an organism
(C) aquatic arthropods that live in marine environments
(D) rocks used by sea otters to dislodge prey and open shells
(E) the act of embracing feverishly
Answer: B
Explanation: Without sea otters, sea urchins and other bottom herbivores would graze on kelp holdfasts. Causing them to drift away from their substrates and die. Without sea urchins and other herbivores, holdfasts attach kelp, hence B is the right answer. The organism, not the holdfast, is the kelps. The passage does not support C, D, or E.
(A) Kelp forests provide a unique habitat for a variety of marine organisms.
(B) Kelp is an important food source for coastal Californians.
(C) Kelp forests occur worldwide throughout temperate and polar coastal oceans.
(D) Kelp is an important part of the sea otter's diet.
(E) A 1911 treaty reinvigorated kelp forests by requiring otter hunters to plant marine algae.
Answer: A
Explanation: The second paragraph concludes: Local extinction of other species and large urchin barrens. Subtidal areas where sea urchin population increase has depleted kelp and other marine species. This sentence shows that kelp deficiency caused marine species deficiency. Thus, kelp provides a unique home for organisms that cannot thrive without it.
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