GWD-5-10

wangtsong

Q9 to Q12:

      The sloth bear, an insect-eating

       animal native to Nepal, exhibits only one

       behavior that is truly distinct from that of

Line       other bear species:  the females carry

  (5)      their cubs (at least part-time) until the

cubs are about nine months old, even

though the cubs can walk on their own

at six months.  Cub-carrying also occurs

among some other myrmecophagous

 (10)      (ant-eating) mammals; therefore, one

explanation is that cub-carrying is

necessitated by myrmecophagy, since

myrmecophagy entails a low metabolic

rate and high energy expenditure in

 (15)      walking between food patches.  How-

ever, although polar bears’ locomotion

is similarly inefficient, polar bear cubs

walk along with their mother.  Further-

more, the daily movements of sloth

 (20)      bears and American black bears—

       which are similar in size to sloth bears

       and have similar-sized home ranges—

reveal similar travel rates and distances,

suggesting that if black bear cubs are

 (25)      able to keep up with their mother, so

too should sloth bear cubs.

      An alternative explanation is defense

from predation.  Black bear cubs use

trees for defense, whereas brown bears

 (30)      and polar bears, which regularly inhabit

treeless environments, rely on aggres-

sion to protect their cubs.  Like brown

       bears and polar bears (and unlike other

myrmecophagous mammals, which are

 (35)
                           noted for their passivity), sloth bears

are easily provoked to aggression.

Sloth bears also have relatively large

canine teeth, which appear to be more

functional for fighting than for foraging.

 (40)     Like brown bears and polar bears,

sloth bears may have evolved in an

environment with few trees.  They are

especially attracted to food-rich

grasslands; although few grasslands

 (45)      persist today on the Indian subcontinent,

this type of habitat was once wide-

spread there.  Grasslands support

high densities of tigers, which fight and

sometimes kill sloth bears; sloth bears

 (50)      also coexist with and have been killed

by tree-climbing leopards, and are often

confronted and chased by rhinoceroses

and elephants, which can topple trees.

Collectively these factors probably

 (55)      selected against tree-climbing as a

defensive strategy for sloth bear cubs.

Because sloth bears are smaller than

brown and polar bears and are under

greater threat from dangerous animals,

 (60)      they may have adopted the extra pre-

caution of carrying their cubs.  Although

cub-carrying may also be adoptive for

myrmecophagous foraging, the behavior

of sloth bear cubs, which climb on their

 (65)      mother’s back at the first sign of danger,

suggests that predation was a key

stimulus.

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Q10:

The author mentions rhinoceroses and elephants (lines 52-53) primarily in order to

             

1. explain why sloth bears are not successful foragers in grassland habitats
2. identify the predators that have had the most influence on the behavior of sloth bears
3. suggest a possible reason that sloth bear cubs do not use tree-climbing as a defense

4. provide examples of predators that were once widespread across the Indian subcontinent
5. defend the assertion that sloth bears are under greater threat from dangerous animals than are other bear species

Answer: C

But I think E is also right.

yuching730

sloth bears
        also coexist with and have been killed

by tree-climbing leopards, and are often

confronted and chased
                by rhinoceroses

and elephants, which can topple trees.

 

提到by rhinoceroses
        and elephants是因为牠们会topple trees

因而造成sloth bears会使用Cub-carrying的行为而不待在树上

因为会受到rhinoceroses
        and elephants的攻击