Transcript:
Differences of behavior have not evolved by chance. Living in close proximity to other animals has certain costs and benefits, so we can expect the group size adopted by a species to be the most suitable for its environment and lifestyle. River dolphins, for example, have a fairly simple social system, forming small groups of just a few animals - rarely more than ten. On the other hand, many of the oceanic dolphins may roam the seas in groups of thousands. Also, there can be differences within species: for example, with sperm whales, females and juveniles form groups while adult males are solitary.
Some of the reasons for living in groups include greater efficiency in searching for and catching food, benefits for mating, learning, defence, and sensory integration. Now, sensory integration is the means by which each animal contributes to the information gained by the group as a whole.
Result:
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Option 1: "Dolphins, whales and porpoises are all social animals, but some species are more sociable than others. This depends on the environment because a species adopts the lifestyle most suitable for this. Among dolphins, forming groups make it easier for them to find food, reproduce and gain knowledge. They are safer, too, because dolphins can communicate danger when there are threats around."
Explanation: This option accurately summarizes the main idea of the text, which discusses the social nature of whales, dolphins, and porpoises, emphasizing the variability in sociability among species based on their environment. It highlights key points such as the benefits of group living for finding food, mating, and safety, which are all mentioned in the text. The phrase 'communicate danger' aligns with the text's discussion on sensory integration and defense.
Option 2: "The speaker explains that whales, dolphins, and porpoises have evolved differently and faced different threats. River dolphin numbers are declining, while ocean dolphins are doing well in spite of the threats they face. The reason for this is that ocean dolphins are better adapted for finding food and avoiding predators."
Explanation: This option incorrectly focuses on the evolutionary differences and threats faced by river and ocean dolphins, which are not the main themes of the text. The text does not mention the decline in river dolphin numbers or compare the adaptation of ocean dolphins to threats. Instead, it emphasizes social behavior and the benefits of group living, making this option misleading.
Option 3: "Dolphins have adopted group living as a response to living in close contact with other animals in the ocean, some of which kill dolphins for food. Living in social groups makes it easier to hunt for food and, in a dangerous environment, it makes sense in terms of safety to move about in large numbers."
Explanation: While this option touches on the idea of group living for safety and hunting, it inaccurately suggests that dolphins live in groups primarily due to the presence of predators. The text does mention safety and hunting benefits, but it also emphasizes other reasons for social behavior, such as mating and learning. This option oversimplifies the text's message and does not capture the full scope of the reasons for social living.
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