SAT Reading - Khan Diagnostic Quiz level 2 - reading 9

Questions 1-11 are based on the following passage.

This passage is excerpted from David B. Wake and Vance T. Vredenburg, "Amphibians in Crisis." ©2008 by The National Academy of Sciences of the USA.

Amphibians have received much attention during the
last two decades because of a now-general understanding
that a larger proportion of amphibian species are at risk of
extinction than those of any other taxon.* Why this should
5 be has perplexed amphibian specialists. A large number of
factors have been implicated, including most prominently
habitat destruction and epidemics of infectious diseases;
global warming also has been invoked as a contributing
factor. What makes the amphibian case so compelling is
10 the fact that amphibians are long-term survivors that have
persisted through the last four mass extinctions.
Paradoxically, although amphibians have proven
themselves to be survivors in the past, there are reasons for
thinking that they might be vulnerable to current
15 environmental challenges and, hence, serve as
multipurpose sentinels of environmental health. The
typical life cycle of a frog involves aquatic development of
eggs and larvae and terrestrial activity as adults, thus
exposing them to a wide range of environments.
20 Frog larvae are typically herbivores, whereas adults are
carnivores, thus exposing them to a wide diversity of food,
predators, and parasites. Amphibians have moist skin, and
cutaneous respiration is more important than respiration
by lungs. The moist, well vascularized skin places them in
25 intimate contact with their environment. One might
expect them to be vulnerable to changes in water or air
quality resulting from diverse pollutants. Amphibians are
thermal-conformers, thus making them sensitive to
environmental temperature changes, which may be
30 especially important for tropical montane (e.g., cloud
forest) species that have experienced little temperature
variation. Such species may have little acclimation ability
in rapidly changing thermal regimes. In general,
amphibians have small geographic ranges, but this is
35 accentuated in most terrestrial species (the majority of
salamanders; a large proportion of frog species also fit this
category) that develop directly from terrestrial eggs that
have no free-living larval stage. These small ranges make
them especially vulnerable to habitat changes that might
40 result from either direct or indirect human activities.
Living amphibians (Class Amphibia, Subclass
Lissamphibia) include frogs (~5,600 currently recognized
species), salamanders (~570 species), and caecilians (~175
species). Most information concerning declines and
45 extinctions has come from studies of frogs, which are the
most numerous and by far the most widely distributed of
living amphibians. Salamanders facing extinctions are
centered in Middle America. Caecilians are the least well
known; little information on their status with respect to
50 extinction exists.
The Global Amphibian Assessment completed its first
round of evaluating the status of all then-recognized
species in 2004, finding 32.5% of the known species of
amphibians to be “globally threatened” by using the
55 established top three categories of threat of extinction (i.e.
Vulnerable, Endangered, or Critically Endangered); 43% of
species have declining populations. In general, greater
numbers as well as proportions of species are at risk in
tropical countries. Updates from the Global Amphibian
60 Assessment are ongoing and show that, although new
species described since 2004 are mostly too poorly known
to be assessed, >20% of analyzed species are in the top
three categories of threat. Species from montane tropical
regions, especially those associated with stream or
65 streamside habitats, are most likely to be severely
threatened.

*A group of one or more populations of an organism or organisms seen by taxonomists to form a unit.

 
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