- Scientists studied an explosion in the population of leaf-cutter ants along roadsides in the Brazilian Cerrado.
- Though it is an iconic and ecologically important species, leaf-cutter ants can cause millions of dollars in crop losses each year even when highly toxic pesticides are in use.
- The researchers are warning of severe ecological and economic impacts as new roads in the Cerrado facilitate the expansion of leaf-cutters into more cropland.
Scientists have discovered what they’re calling an “unintended and ironic” consequence of building roads to aid agricultural expansion in Brazil: those same roads are providing the perfect habitat for insects that can do serious harm to crops.
Ernane Vieira-Neto, a Ph.D. candidate with University of Florida’s Tropical Conservation and Development Program, spent four years in the field in Brazil studying leaf-cutter ants (Atta laevigata). Though it is an iconic and ecologically important species, leaf-cutter ants can cause millions of dollars in crop losses each year even when highly toxic pesticides are in use.
Vieira-Neto teamed up with Emilio Bruna and Heraldo Vasconcelos of Brazil’s Universidade Federal de Uberlandia to study an explosion in the population of leaf-cutter ants along roadsides in the Brazilian Cerrado, a vast tropical savannah comprised of interspersed grasslands and forests that is being converted for agricultural purposes at such an alarming rate that is considered a new global deforestation hotspot.
The Cerrado is largely responsible for Brazil’s emergence as an agricultural superpower, and approximately 4,600 miles of new road are to be built there over the next two decades. Vieira-Neto and team, who have summarized their findings in an article published by the Journal of Applied Ecology this month, found that all those new roads are likely to help leaf-cutters invade more cropland, as the number of ant colonies next to roads is much higher than in nearby areas of native vegetation.
“For population growth, every individual colony and life stage is important,” Vieira-Neto said in a statement. “But events that occur so early in the life cycle of a leaf-cutter ant colony, such as successful colony foundation by the ant queen and colony survival as a juvenile, are more prevalent near roads and have relatively more importance for the population than late-life events.”
The researchers found that 35 to 45 percent of adult leaf-cutter colonies were located within 15 miles of roads, which is significantly higher than if they were dispersed across the landscape at random.
Increased numbers of the ants will likely have consequences for other plant and animal species as well as ecosystem functions like nutrient cycling because of the ants’ role as ecosystem engineers, according to the paper.
Leaf-cutter ants are considered one of the most severe agricultural pests ever encountered, and the researchers predict that their exploding population numbers along new roads in the Cerrado could have major economic impacts.
“No matter where they are built, roads have unintended consequences for native plants and animals,” Bruna said. “Our results suggest that the impacts of roads on native biodiversity can have not only ecological impacts on other plants and animals, but potentially unexpected economic ones as well.”
Road networks are proliferating in biodiversity-rich regions around the globe, with at least 25 million kilometers (about 15.5 million miles) of new roads expected to be built by 2050, as the researchers note in the paper. That means that developing conservation and management strategies for native species whose population numbers are enhanced by roads requires understanding the demographic mechanisms that drive these changes.
“We demonstrate that the higher growth rate of roadside Atta laevigata populations is due to increased early-life performance,” the researchers write in the paper.
“Thus, the expansion of road networks could have major ecological and economic consequences by facilitating the increased abundance of ecosystem engineers and agricultural pests. Accounting for A. laevigata early life stages and careful planning of road placement should improve management strategies of protected areas and agricultural systems in Neotropical savannahs.”
CITATION
Vieira-Neto, E. H. M., Vasconcelos, H. L., Bruna, E. M. (2016), Roads increase population growth rates of a native leaf-cutter ant in Neotropical savannahs. Journal of Applied Ecology. doi:10.1111/1365-2664.12651
