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joyseychow
- Master | Next Rank: 500 Posts
- Posts: 125
- Joined: Mon Dec 15, 2008 9:24 pm
Anole Lizard Species that
occur together (sympatrically)
on certain Caribbean islands
Line occupy different habitats:
(5) some live only in the grass,
some only on tree trunks, and
some only on twigs. These
species also differ morpho-
logically: grass dwellers are
(10) slender with long tails, tree
dwellers are stocky with long
legs, twig dwellers are slender
but stubby-legged. What is
striking about these lizards
(15) is not that coexisting species
differ in morphology and habi-
tat use (such differences are
common among closely related
sympatric species), but that
(20) the same three types of habi-
tat specialists occur on each
of four islands: Puerto Rico,
Cuba, Hispaniola, and Jamaica.
Moreover, the Puerto Rican
(25) twig species closely resembles
the twig species of Cuba,
Hispaniola, and Jamaica in
morphology, habitat use, and
behavior. Likewise, the spe-
(30) cialists for other habitats are
similar across the islands.
The presence of similar
species on different islands
could be variously explained.
(35) An ancestral species might
have adapted to exploit a
particular ecological niche on
one island and then traveled
over water to colonize other
(40) islands. Or this ancestral
species might have evolved
at a time when the islands
were connected, which some
of these islands may once
(45) have been. After the islands
separated, the isolated lizard
populations would have become
distinct species while also
retaining their ancestors’ niche
(50) adaptations. Both of these
scenarios imply that speciali-
zation to each niche occurred
only once. Alternatively, each
specialist could have arisen
(55) independently on each of the
islands.
If each type of specialist
evolved just once, then similar
specialists on different islands
(60) would be closely related.
Conversely, if the specialists
evolved independently on each
island, then a specialist on one
island would be more closely
(65) related to other types of anoles
on the same island—regardless
of their ecological niches—
than it would be to a similar
specialist on a different island.
(70) Biologists can infer how
species are related evolu-
tionarily by comparing DNA
sequences for the same genes
in different species. Species
(75) with similar DNA sequences
for these genes are generally
more closely related to each
other than to species with less-
similar DNA sequences. DNA
(80) evidence concerning the anoles
led researchers to conclude
that habitat specialists on one
island are not closely related
to the same habitat specialists
(85) elsewhere, indicating that spe-
cialists evolved independently
on each island.
Q. According to the passage, sympatric anole lizard species resemble many other closely related sympatric species in that the anole lizard species
A) differ from one another in morphology and habitat use
B) evolved on islands that were once connected
C) appear to have adapted unusually quickly to new habitats
D) have been able to colonize areas remote from their ancestral habitat
E) occupy the same range of habitats in a number of different locations
OA is A, Pls explain. Thks
occur together (sympatrically)
on certain Caribbean islands
Line occupy different habitats:
(5) some live only in the grass,
some only on tree trunks, and
some only on twigs. These
species also differ morpho-
logically: grass dwellers are
(10) slender with long tails, tree
dwellers are stocky with long
legs, twig dwellers are slender
but stubby-legged. What is
striking about these lizards
(15) is not that coexisting species
differ in morphology and habi-
tat use (such differences are
common among closely related
sympatric species), but that
(20) the same three types of habi-
tat specialists occur on each
of four islands: Puerto Rico,
Cuba, Hispaniola, and Jamaica.
Moreover, the Puerto Rican
(25) twig species closely resembles
the twig species of Cuba,
Hispaniola, and Jamaica in
morphology, habitat use, and
behavior. Likewise, the spe-
(30) cialists for other habitats are
similar across the islands.
The presence of similar
species on different islands
could be variously explained.
(35) An ancestral species might
have adapted to exploit a
particular ecological niche on
one island and then traveled
over water to colonize other
(40) islands. Or this ancestral
species might have evolved
at a time when the islands
were connected, which some
of these islands may once
(45) have been. After the islands
separated, the isolated lizard
populations would have become
distinct species while also
retaining their ancestors’ niche
(50) adaptations. Both of these
scenarios imply that speciali-
zation to each niche occurred
only once. Alternatively, each
specialist could have arisen
(55) independently on each of the
islands.
If each type of specialist
evolved just once, then similar
specialists on different islands
(60) would be closely related.
Conversely, if the specialists
evolved independently on each
island, then a specialist on one
island would be more closely
(65) related to other types of anoles
on the same island—regardless
of their ecological niches—
than it would be to a similar
specialist on a different island.
(70) Biologists can infer how
species are related evolu-
tionarily by comparing DNA
sequences for the same genes
in different species. Species
(75) with similar DNA sequences
for these genes are generally
more closely related to each
other than to species with less-
similar DNA sequences. DNA
(80) evidence concerning the anoles
led researchers to conclude
that habitat specialists on one
island are not closely related
to the same habitat specialists
(85) elsewhere, indicating that spe-
cialists evolved independently
on each island.
Q. According to the passage, sympatric anole lizard species resemble many other closely related sympatric species in that the anole lizard species
A) differ from one another in morphology and habitat use
B) evolved on islands that were once connected
C) appear to have adapted unusually quickly to new habitats
D) have been able to colonize areas remote from their ancestral habitat
E) occupy the same range of habitats in a number of different locations
OA is A, Pls explain. Thks
