Sea otter population decline

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The sea otter is a small mammal that lives in waters along the western coast of North America from California to Alaska. When some sea otter populations off the Alaskan coast started rapidly declining a few years ago, it caused much concern because sea otters play an important ecological role in the coastal ecosystem. Experts started investigating the cause of the decline and quickly realized that there were two possible explanations: environmental pollution or attacks by predators. Initially, the pollution hypothesis seemed the more likely of the two.

The first reason why pollution seemed the more likely cause was that there were known sources of it along the Alaskan coast, such as oil rigs and other sources of industrial chemical pollution. Water samples from the area revealed increased levels of chemicals that could decrease the otters' resistance to life-threatening infections and thus could indirectly cause their deaths.

Second, other sea mammals such as seals and sea lions along the Alaskan coast were also declining, indicating that whatever had endangered the otters was affecting other sea mammals as well. This fact again pointed to environmental pollution, since it usually affects the entire ecosystem rather than a single species. Only widely occurring predators, such as the orca (a large predatory whale), could have the same effect, but orcas prefer to hunt much larger prey, such as other whales.

Third, scientists believed that the pollution hypothesis could also explain the uneven pattern of otter decline: at some Alaskan locations the otter populations declined greatly, while at others they remained stable. Some experts explained these observations by suggesting that ocean currents or other environmental factors may have created uneven concentrations of pollutants along the coast.

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Now listen to part of a lecture on the topic you just read about.

Well, ongoing investigations have revealed that predation [a diffıcult word for candidates: enunciate clearly] is the most likely cause of sea otter decline after all.

First, the pollution theory is weakened by the fact no one can really find any dead sea otters washing up on Alaskan beaches. That's not what you would expect if infections caused by pollution started killing a lot of otters. On the other hand, the fact that it's so hard to find dead otters is consistent with the predator hypothesis: if an otter is killed by a predator, it's eaten immediately so it can't wash up on shore.

Second, although orcas may prefer to hunt whales, whales have essentially disappeared from the area because of human hunters. That means that orcas have had to change their diet to survive, and since only smaller sea mammals are now available, orcas have probably started hunting those. So it probably is the orcas that are causing the decline of all the smaller sea mammals mentioned in the passage, the seals, the sea lions, and the sea otters.

And third, the uneven pattern of otter decline is better explained by the orca predation theory than by the pollution theory. What happens to otters seems to depend on whether the location where they live is accessible to orcas or not. In those locations that orcas can access easily, the number of sea otters has declined greatly. However, because orcas are so large, they can't access shallow or rocky locations. And shallow a d rocky locations are precisely the types of locations where sea otter populations have not declined.
问题

Summarize the points made in the lecture, being sure to explain how they respond to the specific points made in the reading passage.

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  • 学员7evIGB
    学员7evIGB
    Firstly, according to the reading passage, there are many water samples showing that industrial chemical pollution may reduce the number of the sea otters. However, in the lecture, the professor argues that since there is no dead otter on the beaches, it seems impossible that the population may decline by environmental pollution. On the other hand, the professor says that no otters on the shore.
    2023-02-07 21:58:59
    学员7evIGB
    学员7evIGB
    The reading passage proposes three possible reasons to explain that populations of the sea otter may decline due to environmental pollution. However, the profeesor says that ongoing investigations have revealed that predation is the most likely cause of sea otter decline after all.
    2023-02-07 21:58:12
    一切为了安多佛
    一切为了安多佛
    378字符 15分钟 呵呵,也是没sei了
    2016-12-12 18:38:06
    一切为了安多佛
    一切为了安多佛
    Finally, the speaker raises the issue that location is better to explain on the predation hypothesis. The areas which the sea otters did not decline are almost on the rocky and shallow areas. This also means that the orcas cannot eat the sea otters. However, in the place like Alaskan coast, the orcas can eat the otters easily; the numbers of sea otters have a great declining. This point disagrees with the point that at some Alaskan locations the otter populations declined greatly, while others they remain stable. The experts think that the environment factors may have created uneven concentrations of pollutants along the coast.
    2016-12-12 18:37:36
    一切为了安多佛
    一切为了安多佛
    Second, the speakers discusses that the human predate too many whales which is the food of the orca which means the orcas do not have enough food. They could eat some small mammals which are available instead the whales. It is inevitable to eat the sea otters, seals and sea lions. In this way, the reason of the declining of the sea otters is the predation of human. Contradicting what is stated in the reading is that other sea mammals such as the seals and sea lions along the Alaska coast were also declining; indicating whatever had endangered the otters was affecting other sea mammals as well. This has been pointed to the pollution hypothesis.
    2016-12-12 18:37:25
    一切为了安多佛
    一切为了安多佛
    First of all, the speaker in the lecture thinks that the pollution hypothesis is better since people cannot find any dead sea otters on the Alaskan beach. The reason that they cannot find is the sea otters were not dead because of the pollution. Instead, their deaths were caused by the predation. That\'s why people cannot find the dead otters on the coast. In contrast, the reading passage believes that there are some known sources on the coast such as the oil rings and other sources of industrial chemical pollution. Plus, the sample of the waters shows that there are increased levels of chemicals that could decrease the otters\' resistance. Under this circumstance, the lecturers totally disagree with the view made in the reading.
    2016-12-12 18:37:12
    一切为了安多佛
    一切为了安多佛
    The lecture is mainly discussing the predation hypothesis of the extinction of the sea otters. Challenging what are stated in the reading passage is that the pollution hypothesis of the extinction of the otters.
    2016-12-12 18:36:57
    airlianna
    airlianna
    范文不好....是以 lecture based 不是reading base, kind of flipping
    2016-03-09 16:31:52
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