Questions 31-40 are based on the following passage.NATURAL SCIENCE: This passage is adapted from the article "The Next Wave: What Makes an Invasive Species Stick?" by Robert R. Dunn (©2010 by Natural History Magazine, Inc.).
Like many biologists, Andrew V. Suarez struggled
for years with the question of which colonizing organ-
isms fail and which succeed. He studied it the hard
way-with fieldwork and lab experiments-until 1999,
5 when he found some brown jars. He had gone to the
Smithsonian Institution National Museum of Natural
History's National Insect Collection to look for early
samples of Argentine ants collected in the United States
or at its borders. He hoped to find out how vintage
10 specimens of Argentine ants were related to the existing
At the museum, among many thousands of jars of
insects labeled with taxonomic notes, locations, and
dates, Suarez ultimately found relatively few samples
15 of Argentine ants. But what he found besides them was,
to his mind, far more interesting: some of the ethanol-
filled jars were jammed with vials of ants collected at
ports of entry in the eastern U.S. from 1927 to 1985.
They were ants that border agents had picked from
20 plants being shipped into the U.S. Could those ants be
identified as members of species that had failed or suc-
ceeded as colonists, and if so, could the specimens be
used to compare the two groups?
In the jars and vials were 394 separate samples of
25 ants. Suarez solicited the help of two friends, ant ecolo-
gist David A. Holway of the University of California,
San Diego, and Philip S. Warp, guru of ant gurus, at the
University of California, Davis. Altogether they identi-
-fied 232 distinct species.
30 Suarez considered the traits possessed by each of
the ant species, in an attempt to see what might have
predisposed some of them to survival. He measured
whether they were big or small. He exaimined whether
each lived in the canopy or on the ground, and whether
35 they were from one subfamily or another. He also
looked at a simpler possibility: that "survivor species"
tended to be those introduced more than once. The evi-
dence in the jars showed, for example, that Argentine
ants had arrived at least twice. Were successes just a
40 consequence of the number of tries?
When a pioneering group sets up camp and starts
living in a new place, possible futures diverge. One
species might be wiped out within a generation or two.
A second might survive, but never become common.
45 Yet another species might thrive,eventually spreading
across states, continents, and even the world! Even if
surviving in a new environment is sometimes a matter
of being introduced again and again, thriving is a differ-
ent story. Relatively few invasive species truly prevail.
50 One curious thing about Argentine ants is that they
are, despite their apparent meekness, ecologically dom-
inant. They are squishy, small, stingless wimps, as ants
go, yet somehow they have managed to overpower the
big, tough native ants.
55 There's another strange thing about Argentine
ants. If you take an Argentine ant from what looks like
one colony and put it together with one from a distant
colony, they accept each other. In fact, you can perform
that trick over much of California and very few of the
60 ants will fight. It is as though all of the Argentine ants
in California are part of a few huge colonies-"super-
colonies," they've come to be called.
Biologist Ted Case joined forces with Holway and
Suarez for an experiment to test whether the lack of
65 aggression among those ant colonies somehow helped
them to compete with other species. Might it simply be
that by not fighting with their neighbors, the Argentine
ants wasted less energy on war and could spend more
time on the good stuff? It turned out that, yes, aggres-
70 sive ants wasted energy fighting (and dying), and so
gathered less food and fared poorly, in general. Peace
pays (at least peace with one's kin), and so Argentine
ants have made bank everyplace they have moved
In fact, it isn't just for the Argentine ant that peace
75 seems to pay. Supercolonies and the unicolonial popu-
lations they create look to be common among invasive
Ants flash chemica1 badges identifying their home
nest. Without such markers, no one knows who is friend
80 or foe. When the clarity of "us versus them" breaks
down, peace breaks out among colonies of an ant
species. Different nests swap workers and queens, and
the term "colony" becomes fuzzy. Experiments seemed
to show that one conglomeration of Argentine ants
85 stretched the length of California, another from Italy to
Portugal ... until, in 2009, workers from those two
"colonies" (along with a third fom Japan) were put
together, and they didn't fight. Thus, across the entire
globe, a few peaceful supercolonies could exist and