#19 - Concept Reference, Must Be True, Purpose/Function

[Administrator]

Complete Question Explanation

The correct answer choice is (E).

Answer choice (A):

Answer choice (B):

Answer choice (C):

Answer choice (D):

Answer choice (E): This is the correct answer choice.

This explanation is still in progress. Please post any questions below!

[ChicaRosa]

I thought it was C because of ln 49-54 but I think I misunderstood it into thinking that just because existing species in the low lands adapted to climate changes means that they survived climatic disturbances.

Is E correct because of the same ln reference that I misapplied to answer choice C?

Thanks!

[Adam Tyson]

The idea here, Chica, is that the Amazon may not have had as stable a climate as previously thought, and climatic instability tends to lead to two things - extinctions and adaptations. In the Amazon, though, it rarely led to extinctions because even when the lowland climate changed, the upper regions remained stable, and so species that had been spread all around avoided extinction in those upper areas. Meanwhile, down in the dry lowlands, adaptations happened, accounting for the rich diversity of species found in the Amazon.

In order for this explanation to make sense, the dry periods need to have happened more than just once or twice. Otherwise, they wouldn't account for a lot of adaptations (speciation). Since we know that there is a lot of speciation/diversity in the Amazon, for this unstable climate/ice age dry spots theory to work there must have been a lot of these dry periods. That's what this info is about - telling us that it happened often enough, instead of just once of twice, to account for the rich diversity of species in the Amazon.

So it's not just about those lines you cited, but about the passage as a whole. The information that these ice ages occurred so many times helps support the overall thesis that diversity in the Amazon is not due to a stable climate, but due to a changing climate. If there had only been one or two ice ages, the argument would be much less persuasive. See how that works?

Keep at it, you'll get there!

[ljuarez3]

When I was doing these questions, I interpreted D and E to be the same thing. So I was taking too long but ultimately chose D. Can someone please explain why it is not D?

[Jeff Wren]

Hi ljuarez,

Question 19 is asking why the author mentions the number of ice ages in the third paragraph.

The third paragraph describes Haffer's explanation for the puzzling distribution of species in the Amazon basin. Basically, his explanation is that during the ice ages, populations of animals would go to the highland wetter "island" refuges to escape the dry lowland areas.

In lines 45-47, the author notes that Haffer's explanation appears to explain both the distribution of the species as well as the high species diversity. The author then explains that the "periodic geographic isolation" (line 49) would have facilitated new species. The author then cites the estimated number of ice ages to support that there were these periodic geographic isolations (while 13 may seem like a small number in some contexts, it is a significant number in the context of ice ages).

This is what Answer E correctly describes.

As for Answer D, it states, "suggest that certain kinds of climatic disturbances cause more species diversity than do other kinds of climatic disturbances." The author makes no comparison between different types of climatic disturbances.

The initial explanation for the diversity of species in the Amazon basin discussed in paragraph one (Sanders's explanation) was that it was due to climatic stability (meaning no climatic disturbances). Also, while the author does mention other types of climatic changes in the final paragraph (storms and flooding - line 57), no direct comparison is made between these and the ice ages.