Logical Reasoning

PT145 · S2 · Q19 A recent study examined the daytime

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A recent study examined the daytime and nighttime activity patterns of two populations of tree-dwelling lemurs—the first living in a rain forest, where tree canopy cover is consistent year-round, and the second living in a deciduous forest, where many trees lose their leaves during the winter months.

Comparing the Two Populations

population 1 population 2

both tree-dwelling lemurs

both more nocturnal activity during winter

live in rain forest live in deciduous forest

tree canopy many trees consistent lose leaves year round during winter

small winter increase big winter increase in nocturnal activity in nocturnal activity

Evaluate / Goal

We need to explain how the rainforest lemurs are different from deciduous lemurs, in regards to why the deciduous lemurs have a bigger uptick in nocturnal activity during the winter.

Since we were told one difference between the two (year-round canopy vs. lose leaves), we anticipate that the correct answer will "Use that difference to explain this difference".

How come the lemurs who live in trees that "lose leaves during winter" are doing "more nocturnal activity" than are the lemurs who live in trees that ?

19.

Which one of the following, if true, most helps to explain the difference between the two lemur populations with respect to winter activity patterns?

  1. For both lemur populations, the

    No Impact / No Distinction

    This helps explain why both lemur populations have an incentive to hunt for food nocturnally (fewer competitors), but this does nothing to explain why one group's nocturnal activity was significantly more than another's. It doesn't point to a factor that would be different between the two groups of lemurs.

    3% picked this

  2. Correct

    The primary predators for both

    Why this is right

    This points to a similarity, when we're looking for a difference, but wait — when it comes to a tree-dwelling lemur population that lives in trees with a full canopy leaves vs. a population that lives in trees where the leaves have fallen off (in winter), will they have different experiences of a "high-flying birds, their primary predator, which relies on eyesight to hunt prey during the day"? Sure! Since the bird is looking below, at the tops of trees, the lemurs who live underneath a canopy of leaves are much better hidden than are lemurs who live in a tree with no leaves. If you're a lemur who lives in a tree with no leaves in it, and you're primarily hunted by birds that use their eyesight to find you during daylight, then you're not going to want to be making yourself seen during the day. You'll keep your activity real low; try to stay hidden and motionless, so that the predator birds don't see you. You'll have to do your hunting for food at night, when the darkness will prevent the high-flying birds from being able to see you as well. Meanwhile, if you're a lemur living in a rain forest with a constant canopy of leaves, then it doesn't really matter whether you're out in the day or at night. The high-flying birds can't see past the canopy of leaves to see you moving about.

    Skill tested: Paradox · how this choice captures the argument's function is the move to repeat next time.

    70% picked this

  3. In both habitats, species of

    No Impact / No Distinction

    This answer might help explain why both populations have more nocturnal activity in the winter. Both of them are thinking, "Shoot — I wanna go out during the day, but I know in the winter there's an uptick of predatory snakes moving around during daylight. I'll just wait until it gets dark." This doesn't do anything to explain the difference though, because we don't have any common sense reason to think that rainforest lemurs would have a different experience of these snakes than deciduous lemurs would, so we don't have way to explain why deciduous lemurs are so much more active at night than rainforest lemurs are.

    5% picked this

  4. The lemur population in the

    No Impact - Population Size

    The raw numbers of population size doesn't explain why the smaller population engages in way more nocturnal activity than the bigger population does. There's no common sense link between being a smaller population and thus having a bigger uptick in nocturnal activity during the winter.

    4% picked this

  5. The lemur population in the

    Unclear Impact

    This does provide a difference between the two populations, but there isn't a common sense link between this difference and the one we know. Rainforest lemurs (year-round canopy of leaves, eat plants and insects, small uptick in nocturnal behavior during winter) vs. Deciduous lemurs (lose leaves during winter, eat only plants, big uptick in nocturnal behavior during winter) There's no obvious sense of why "if you eat only plants (rather than plants and insects), then you'll have a bigger uptick in nocturnal behavior during the winter".

    18% picked this

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