Aaron Flesch, a University of Arizona researcher who has worked along the border since 1996, said the long-term impacts are hard to predict, but the negative consequences are certain.

“Cutting off connectivity, in almost all cases, is going to be bad,” Flesch said. “We don’t know if it’s necessarily going to cause extinction of either sub-population on either side of the border, but it’s definitely going to (increase) the probability of it.”

But researchers have identified the effect of existing man-made barriers on species’ abilities to find food, water and mates along the border.

Mexican Federal Highway 2, which closely parallels the U.S.-Mexico border and spans 1,219 miles, from Tijuana in Baja California to Playa Bagdad in Tamaulipas, has proved impassable for some species.

The highway presents a case study in what Trump’s “big, beautiful wall” would mean for many species along the border, scientists say.

Part of the highway borders the southern edge of Arizona’s Cabeza Prieta National Wildlife Refuge, fragmenting the habitat of the Sonoran pronghorn, one of the most endangered species in the region.

The highway, along with two others bordering the refuge, irreparably harmed the ability of pronghorns to naturally recover from environmental stressors like droughts and erosion, cutting them off from water and food, and limiting genetic diversity, according to researchers and reports detailing species recovery efforts.

Jim Atkinson, the Sonoran pronghorn recovery coordinator for the wildlife refuge, said the species would have gone extinct were it not for extensive bi-national recovery efforts – at the cost of tens of millions of dollars – by both the U.S. and Mexico.

“They’re very nomadic and they could pretty much wander wherever they needed to go seasonally,” Atkinson said. “It’s all driven by, where’s the water and where’s the food? Now, we’ve got a landscape like Cabeza (Prieta) that’s defined by highways.”

And Arizona wildlife would be affected more than other border states, researchers say, because many of the existing barriers along the state’s section of the border still allow some animals to cross.

Of the 376 miles that make up the Arizona-Mexico border, 142 are lined with various kinds of pedestrian fencing, or fence structures designed to stop border crossers traveling by foot, according to information provided by U.S. Customs and Border Protection. Another 183 are lined with vehicle barriers, made up of metal posts – sometimes crosshatched – and designed to stop cars from driving over border terrain. Only 51 miles have no barrier.

Vehicle barriers, which line about half of the Arizona border and allow most species to cross, have been placed along some portions of the Sky Islands section of the border. But in other parts of the Sky Islands, wildlife movement has been inhibited by more obtrusive fencing.

“A lot of the populations in the borderlands of Sonora seem to be dependent on movement in southern Arizona,” Flesch, the UA researcher, said.

When a species is divided by a barrier, and a catastrophic event, like fire or flood or drought, diminishes the population, Flesch said, the divided species faces a more difficult recovery, and risks a greater chance of extinction.

‘We’re altering the whole food system’

Researchers working for the Tucson-based Sky Island Alliance want to more definitively demonstrate what effect a wall would have on the wildlife in the Sky Islands.

“An impassable border wall would make it very difficult for a lot of species to live in this area to continue to exist,” Bryon Lichtenhan, one of the group’s field coordinators, said.

The group had already placed motion-sensor cameras in some areas of the Sky Islands, further from the border, to study specific wildlife groups and areas. In July, they moved the cameras to border-crossing passages in areas of the Patagonia and Huachuca mountains, where researchers suspected they would find rarer species that haven’t been directly observed.