Brian Owens in Nature:
With Republican presidential candidate Donald Trump talking about walling off the United States from Mexico, ecologists fear for the future of the delicate and surprisingly diverse ecosystems that span Mexico’s border with the southwestern United States. “The southwestern US and northwestern Mexico share their weather, rivers and wildlife,” says Sergio Avila-Villegas, a conservation scientist from the Arizona-Sonora Desert Museum in Tucson. “The infrastructure on the border cuts through all that and divides a shared landscape in two.” Trump’s policies tend to be short on detail, but he has talked about sealing off the entire 3,200-kilometre border with a wall that would be 10–20 metres high. “We will build a wall,” Trump says in a video on his campaign website. “It will be a great wall. It will do what it is supposed to do: keep illegal immigrants out.” Constructing a wall “would be a huge loss”, says Clinton Epps, a wildlife biologist at Oregon State University in Corvallis. “We know how important the natural movement of wildlife is for the persistence of many species.” Far from being a barren wasteland, the US–Mexico borderlands have some of the highest diversity of mammals, birds and plants in the continental United States and northern Mexico — including many threatened species.
A wall could divide species that make a home in both nations. Bighorn sheep, for example, live in small groups and rely on cross-border connections to survive, says Epps. Other species, such as jaguars, ocelots and bears, are concentrated in Mexico but have smaller, genetically linked US populations. “Black bears were extirpated in West Texas, and it was a big deal when they re-established in the 1990s,” Epps says. Breaking their links with Mexican bears could put the animals at risk again. And birds that rarely fly, such as roadrunners, or those that swoop low to the ground, such as pygmy owls, could also have trouble surmounting the wall. Such a physical barrier would worsen the habitat disruption caused by noise, bright lights and traffic near the border. And a wall would cut across rivers and streams that cross the border, severing a vital link. “When water crosses the border, it unites ecosystems,” says Avila-Villegas. “If we block the water, it affects nature on a much more fundamental level.”