Estimates of the number of invasive species vary widely: according to the U.S. Eurasian garlic mustard is a common target of volunteer weed-pulls organized by local parks departments. and Canada spend tens of millions of dollars a year to keep Asian carp out of the Great Lakes. Today, governments and non-profits dedicate considerable resources to controlling invasive species. But by the 1990s, it was driving public policy. In 1859, he wrote that “natural selection … adapts the inhabitants of each country only in relation to the degree of perfection of their associates,” so organisms that evolved under more difficult conditions have “consequently been advanced through natural selection and competition to a higher stage of perfection or dominating power.” It would be another 125 years before invasion ecology coalesced as a subfield. cattle populations.Ĭharles Darwin was perhaps the first to posit the idea that introduced species might outcompete natives. In an era of renewed focus on borders, it’s hard to ignore the similarities between how we talk about non-native animals-hyper-fertile “foreigners” colonizing “native” ecosystems-and the words some use to discuss human immigration. And as international relations have become more heated, so too has the debate among researchers over the pointed rhetoric we use to talk about animals, plants and micro-organisms that hail from elsewhere.Īs cattle fever ticks expand their range, "tick riders" patrol a 500-mile quarantine line to protect U.S. In a recent essay, New School environmental studies professor Rafi Youatt wrote that a trip to Texas left him contemplating “the opposition of invasiveness to nativeness and purity” and “the many ways that invasiveness attaches to both human and nonhuman life.” The parallel has not been lost on those who study invasive species. If caught, these immigrants-often referred to as "aliens” by the media or even “illegals” by the president-face arrest and deportation. immigration officers patrol their own line, looking for signs of illegal human immigration into the United States. For decades, both scientists and laypeople have referred to organisms like the Nilgai as “alien,” “exotic” and “invasive.” But as long as ecologists have warned about the danger of invasive species, others have asked whether this kind of language-which carries connotations of war and xenophobia-could cloud the science and make rational discussion more difficult. The differences in how authorities treat domesticated cattle, native deer and wild, imported antelope illustrate a stark divide in ecology. Fish and Wildlife Service sponsors regular Nilgai hunts in protected areas. That’s why, unlike native white-tailed deer-which also host ticks-they are subject to an unrestricted hunting season, and the U.S. They are cursed not only for their role as a disease vector, but because they eat native plants and compete with cattle for food. These antelope, like the ticks themselves, and the pathogen they carry, are considered an invasive species. Yet despite their best efforts, the tick riders' challenge has recently increased, as more and more of the hardy ticks find their way across the border.Ī large part of the problem is that cattle fever ticks also have another host: Nilgai antelope, a species native to India that was imported to North America in the 1930s as an exotic target for game hunters. Whenever they find a stray or infected cow, they track it down and dip it in pesticide to kill the ticks and prevent them from spreading. The USDA's “tick riders,” as they are called, are tasked with keeping infected cattle from straying deeper into Texas, where the deadly fever poses a serious threat to the beef industry. And their purpose is to keep out the ticks that carry cattle fever, a deadly bovine disease endemic to Mexico. Border Patrol-they’re employees of the U.S. Their mission: to protect their country from would-be invaders. In South Texas, government agents patrol a barrier line that snakes some 500 miles along the course of the Rio Grande. Nilgai antelope, like the cattle fever ticks they carry, are considered an invasive species in places like Texas.