US-Mexico border fence putting wildlife at risk of extinction

Arroyo Toad (Bufo californicus).The construction of fences along the US-Mexico border has emerged as a social hot-button issue over the last decade. As a new study illustrates, these controversial fences also create extinction risks for some species of wildlife.

Jesse Lasky from the University of Texas and fellow researchers have conducted one of the first comprehensive assessment of how fencing along the US-Mexican border affects wildlife. The study, published in the journal Diversity and Distributions, looks at how current and future barriers along the border intersect with the ranges of 313 species of amphibian, reptile, and non-flying mammal mammals.

They came up wtih criteria for risk of global extinction and risk of local extinction. To determine risk, they looked at a number of factors including the proportion of the species range that encompassed areas with borders barriers.

They found that current fencing along 600 km of the border places 27 species at greater risk of global extinction including the endangered arroyo toad and black-spotted newt. They also found that border fences place 23 species at greater risk of loss of local populations.

The push for stronger response to illegal immigration has led to the construction of hundreds of miles of fences and walls - typically 4.5 meters tall or higher with little or no openings.

Barriers such as extensive border fencing can harm species in a number of major ways. They can eliminate connectivity among populations leading to genetic problems in the species through reduced gene flow. Barriers can also lead to remnant populations that are too small to be viable.

The study found that three border regions - California,  the Gulf Coast and the Madrearn archipelago - faced the greatest risk to species. These regions all share characteristics of high species richness within narrow ecological gradients.

The researchers only assessed risk rather than actual impact. Nevertheless, the results point the way for future studies to find empirical evidence that the barriers are indeed having a negative impact on species. They also give guidance for mitigation efforts as the barrier fencing is extended along the border in the future.

--by Rob Goldstein

Lasky, J., Jetz, W., & Keitt, T. (2011). Conservation biogeography of the US-Mexico border: a transcontinental risk assessment of barriers to animal dispersal Diversity and Distributions, 17 (4), 673-687 DOI: 10.1111/j.1472-4642.2011.00765.x