What's the Difference Between Invasive and Nonnative Species? Plus, More Questions From Our Readers

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How long does a plant or animal species have to live in a region before it is considered native? And are all non-native species considered invasive?

Katherine Sabia, Monroe, Connecticut

The distinction between native and nonnative species does not disappear over time; if a plant or animal was introduced with human help, according to the Department of Agriculture, it is nonnative. There’s also a crucial distinction between nonnative species and invasive ones, notes Vicki Funk, senior research botanist and curator at the Museum of Natural History. To be considered invasive, a nonnative animal or plant species has to displace one or more natives. Chicory, introduced from Europe as a flavoring agent in the 19th century, grows wild in the United States but does not displace native plants; but kudzu, introduced from Asia for erosion control in the mid-20th-century South, does, and is considered therefore invasive.

After researchers tag or collar an animal, does the device ever lead to the animal being ostracized from its group?

John Fleming, Rockport, Massachusetts

Studies have found that African zebras wearing heavy collars may change their travel routes, and that collared water voles in the United Kingdom bear fewer female offspring, but the social implications of collaring have not been extensively researched. Peter Leimgruber, head of the Conservation Ecology Center at the Smithsonian Conservation Biology Institute, who studies Przewalski’s horses, says he has observed no negative effects on the social ranking, behavior or fitness of those horses, or on that of other collared equines. In fact, one of the goals of collaring animals is to record their behavior in order to better understand their social structure.

How did the word “volume” become associated with sound?

Raymond Stubblefield, Harrisonburg, Virginia

The word has several threads in modern English, says Mary S. Linn, curator of cultural and linguistic revitalization at the Center for Folklife and Cultural Heritage. When it entered English, in the late 14th century, it referred to a roll of papyrus and to a bound book. As books grew larger, “volume” referred to bulk more generally. By the late 18th century, according to the Oxford English Dictionary, scientists extended the meaning to refer to bodies of matter occupying space, and musicians used it to refer to the power of voices to project in a space.

How long would it have taken the United States to build a third atomic bomb after it dropped the second (and last) one on Nagasaki on August 9, 1945?

Gary Miller, Davenport, Florida

Less than two weeks. Michael Neufeld, senior curator at the National Air and Space Museum, says that on August 10, 1945, Maj. Gen. Leslie Groves, director of the Manhattan Project, notified the War Department that another plutonium bomb could be “ready for delivery on the first suitable weather after 17 or 18 August.” Documents from the era reveal that the United States was prepared to build at least 12 more bombs before Japan surrendered, on August 15.

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