Read the following passage and the lecture which follows. In an actual test, you would have 3 minutes to read the passage. Then, answer the question. In the test, you would have 20 minutes to plan and write your response. Typically, an effective response will be 150 to 225 words. Test takers with disabilities may request additional time to read the passage and write the response.
Sea otters are a small mammal that lives in the waters along North America's west coast from California to Alaska. A few years ago some of the sea otter populations off of the Alaskan coast started to decline rapidly and raised several concerns because of their important role in the coastal ecosystem. Experts began investigating and came up with two possible explanations. One explanation was environmental pollution and the second was attacks by predators.
At first it seemed as if the pollution was the most likely cause for the population decline. One reason pollution was more likely was because of the known pollution sources along the Alaskan coast such as oil rigs. Also water samples taken in the area showed increased levels of chemicals that could decrease the otters' immune systems and indirectly result in their deaths.
Another thing that pointed to pollution as the culprit was the decline of other sea mammals such as seals in the same areas. This indicated that whatever was affecting the otters was also affecting the other sea mammals. Environmental pollution usually affects an entire ecosystem instead of just one species. Only predators that occurred in a large area, such as orcas (a large predatory whale), could cause the same effect, but they usually hunt larger prey.
Finally, scientists believed the pollution hypothesis would also explain the uneven pattern of otter decline. In some Alaskan locations the otter population declined greatly while other populations remained stable. Some experts suggested this could be explained by ocean currents, or other environmental factor, might have created uneven concentrations of pollutants along the coast.
Professor: Ongoing investigations have shown that predation is the most likely cause of the sea otter decline after all.
First, there is a lack of dead sea otters washing up on Alaskan beaches which is not what you would expect from infections caused by pollution killing them off. However, the fact that dead otters are seldom found supports the predator hypothesis. If a predator kills an otter, then it is eaten right away and can't wash up on shore.
Second, orcas prefer to hunt whales, but whales have essentially disappeared in that area from human hunters. Since the whales are not as available, orcas have had to change their diet to what is available. Since it is only smaller sea animals available, the orcas have probably started hunting those more and created the decline in all of the species mentioned in the passage.
Finally, predation is a more likely reason for the uneven pattern of otter decline. Otters in locations that are more accessible to orcas are more likely to be hunted. This is supported by the stable populations of otters in shallow rocky locations where orcas can't access.
Summarize The Point Made In The Lecture And Explain How The Speaker Cast Doubt On Specific Points Made In The Reading Passage.
During a few years ago, some sea otter populations off the Alaskan coast started declining. Based on expert investigations, there are two feasible explanations: environmental pollution and attacks by predators. The passage says that the pollution hypothesis is more important, however, the professor in the lecture claims that predation is the more important cause for otters’ decline.
The first reason which is mentioned in the passage explains that oil and industrial chemical pollutions infect the otters' settlement and cause their deaths. But the professor disagrees with this point of view and says because nobody find any dead sea otter washing off on beaches, so the pollution hypothesis are weakened. On the other hand, predation hypothesis is strong enough is this case, because the predators eat immediately the otters after prey and you can not see any dead sea otter.
Second, It is assumed in the passage that whatever had endangered the otters was affecting other sea mammals like seals and sea lions which were declining. The passage explains that only orca could have the same effect which is interested in other whales. The lecture corrects this statement by saying that whale are disappeared by human hunters. Therefore, orcas changed their diet and have eaten small mammals like sea lions and seals!
Third, the passage believes the uneven pattern of otter decline based on pollution hypothesis however the lecture based on the predation. The professor explains that the accessibility of the otters' location to orcas is very important in declining their population. The number of the otters in shallow and rocky locations has not declined because the orcas could not enter into this area.