Like many biologists, Andrew V. Suarez struggled for years

NATURAL SCIENCE: This passage is adapted from the article “The Next Wave: What Makes an Invasive Species Stick?” by Robert R. Dunn

Like many biologists, Andrew V. Suarez struggled for years with the question of which colonizing organisms fail and which succeed. He studied it the hard way — with fieldwork and lab experiments — until 1999, 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 specimens of Argentine ants were related to the existing populations.

At the museum, among many thousands of jars of insects labeled with taxonomic notes, locations, and dates, Suarez ultimately found relatively few samples 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 plants being shipped into the U.S. Could those ants be identified as members of species that had failed or succeeded 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 ants. Suarez solicited the help of two friends, ant ecologist David A. Holway of the University of California, San Diego, and Philip S. Ward, guru of ant gurus, at the University of California, Davis. Altogether they identified 232 distinct species.

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 examined whether each lived in the canopy or on the ground, and whether 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 evidence in the jars showed, for example, that Argentine ants had arrived at least twice. Were successes just a 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. 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 different story. Relatively few invasive species truly prevail.

One curious thing about Argentine ants is that they are, despite their apparent meekness, ecologically dominant. They are squishy, small, stingless wimps, as ants  go, yet somehow they have managed to overpower the big, tough native ants.

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 ants will fight. It is as though all of the Argentine ants in California are part of a few huge colonies — “supercolonies,” they’ve come to be called.

Biologist Ted Case joined forces with Holway and Suarez for an experiment to test whether the lack of 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, aggressive 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 seems to pay. Supercolonies and the unicolonial populations they create look to be common among invasive ants.

Ants flash chemical badges identifying their home nest. Without such markers, no one knows who is friend 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
stretched the length of California, another from Italy to Portugal . . . until, in 2009, workers from those two “colonies” (along with a third from Japan) were put together, and they didn’t fight. Thus, across the entire globe, a few peaceful supercolonies could exist and expand.

31. The main purpose of this passage is to:

A. describe events that led to the discovery of Argentine ants in the United States.
B. examine the physical differences between Argentine ants and other insects.
C. highlight the technology that scientists used to determine the size of supercolonies.
D. discuss factors that contribute to a colonizing organism’s success as an invasive species.

32. The author makes repeated use of which of the following in order to help establish the passage’s somewhat casual tone?

F. Personal anecdotes
G. Idiomatic expressions
H. Humorous quotations
J. Self-critical asides 

33. Which of the following events mentioned in the passage occurred first chronologically?

A. Case joined Holway and Suarez to assist them with an experiment.
B. Workers from three Argentine ant supercolonies in different parts of the world were brought together.
C. Suarez found samples of Argentine ants in the Smithsonian insect collection.
D. Holway and Ward were recruited by Suarez to assist with his research.

34. The main purpose of the fifth paragraph (lines 41–49) is to:

F. explain how Argentine ants are able to survive in new areas and discuss their spread throughout the world.
G. describe possible outcomes for a pioneering species and stress the improbability that the species will thrive.
H. define the concept of invasive species as it relates to ants.
J. compare the behaviors of Argentine ants to those of other, more successful pioneering species.

35. The author’s claim that the Argentine ant behavior described in lines 56–58 is unusual is based upon which of the following assumptions?

A. Supercolonies are common among several species of ants.
B. Argentine ants in California are less aggressive than Argentine ants elsewhere.
C. California’s ecosystem is especially suited for Argentine ants.
D. Ants from different colonies typically fight one another.

36. According to the passage, the question of which colonizing organisms fail and which succeed is one that has been studied by:

F. many biologists for a number of years.
G. many biologists beginning in 1999.
H. the Smithsonian exclusively.
J. Suarez exclusively.

37. The passage makes clear which of the following about the ant samples Suarez found in the Smithsonian insect collection?

A. Most of the samples were of Argentine ants.
B. Ward and Holway had collected the samples as part of a larger study of US insect populations.
C. Suarez discovered that most of the samples were of previously undiscovered species of ants.
D. Suarez was most interested in the samples that had been collected at eastern US ports of entry.

38. According to the passage, which of the following is true of Argentine ants?

F. They are stingless.
G. They are physically dominant.
H. They were first discovered in the United States by Suarez.
J. They have failed to thrive in Japan.

39. The passage indicates that compared to peaceful ants, aggressive ants:

A. live in larger colonies.
B. spend less time gathering food.
C. are less likely to live in a colony.
D. are more likely to be a “survivor species.”

40. The passage most clearly establishes which of the following facts about ants?

F. In order for ant colonies to combine to form supercolonies, the colonies must have identical chemical badges.
G. Ants identify their home nests by flashing chemical badges.
H. Ant colonies from different species commonly swap workers and queens.
J. The largest supercolony of ants in the world stretches from Italy to Portugal.


31. The best answer is D because the passage focuses on Suarez’s research on colonizing ants and his conclusions about what enables some species to survive over others.

32. The best answer is G because peppered throughout this passage are certain colloquial phrases not often seen in scientific tracts, including that a scientist did it “the hard way” (lines 3–4), that one scientist was the “guru of ant gurus”, that Argentine ants were “wimps”, and that certain species always “made bank”. The use of such relaxed language helps create a casual tone for the reader.

33. The best answer is C because the first paragraph tells readers that Suarez “found some brown jars” at the Smithsonian in 1999, meaning this event occurred before the turn of the century, well before the other choices.

34. The best answer is G because the opening sentence of the fifth paragraph states the focus of the paragraph: that when a group moves to a new area, “possible futures diverge”. What follows in the paragraph are examples of these possible futures and the indication that it’s unlikely for a species to survive, let alone thrive in a new area.

35. The best answer is D because lines 56–58 state that if Argentine ants from different colonies are placed together, “they accept each other.” This is noted directly after line 55 describes this as “strange” behavior, so it can be assumed that in most similar situations ants would fight one another, not accept one another.

36. The best answer is F because lines 1–3 state that Suarez was “like many biologists” who “struggled for years with the question of which colonizing organisms fail and which succeed.

37. The best answer is D because lines 15–18 state that what Suarez found in the brown jars other than Argentine ants was “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.” Those ants provided the basis for Suarez’s research.

38. The best answer is F because line 52 clearly states Argentine ants are “squishy, small, stingless wimps.”

39. The best answer is B because lines 69–71 say that studies show that “aggressive ants wasted energy fighting (and dying), and so gathered less food and fared poorly.”

40. The best answer is G because this fact is stated clearly in lines 78–79: “Ants flash chemical badges identifying their home nest.”