Like Canaries in a Coal Mine, Dragonflies Signal Threats to Freshwater Ecosystems
In gauging the growing threats to freshwater biodiversity, dragonflies and damselflies are viewed by ecologists as sentinels, reacting to threats by seeking out more stable homes. In a new study, researchers report that many of these aquatic insects are likely to begin relocating in coming decades as climate change makes their habitats warmer and drier.
The study, published in the journal Diversity and Distribution, focuses on potential changes in the distribution of dragonflies and damselflies in Central and Western Asia and the Middle East. Using computer modeling, scientists plotted the distribution of 159 species spanning 24 countries, comparing a snapshot of their presence today with projections for the years 2070 and 2100. Their findings have broad implications for freshwater ecosystems.
While none of the species studied are expected to disappear solely because of climate change, according to the study, the researchers found that some species of both dragonflies and damselflies are likely to be driven to near-extinction by 2100 as a result of both climate patterns and ongoing human actions that degrade their habitats. Those human impacts can range from changes in water flow because of damming or irrigation to the introduction of invasive species and the overexploitation of species.
The researchers pointed to Onychogomphus macrodon, for example—a dragonfly better known as the Levant pincertail, native to Israel, Jordan, Lebanon, Syria and Turkey—as a victim of human actions, including dam construction, gravel mining and water pollution.
“We will be seeing changes to freshwater environments,” said John Cadena, the lead author of the study and a former graduate student at Utrecht University. “Dragonflies are keystone species integral to the freshwater system as a predator and a prey.”
“We try to maintain and protect them by identifying what could happen in the future,” he added.
The researchers found that dragonflies and damselfly species in Azerbaijan; Cyprus; western and southern Turkey, and the Levant, or countries bordering the eastern Mediterranean, will probably experience a decline in biodiversity by 2070 and 2100, whereas an increase is anticipated in Armenia, eastern Turkey and eastern Central Asia.
Areas that are the most species rich in species are expected to suffer the greatest declines: 20 to 30 percent in parts of western Turkey, the Levant, the southern Caucasus and northern Iran, the report states.
Most of the areas studied are “expected to become warmer and drier, resulting in freshwater habitats disappearing or desiccating in the warmest, driest part of the year,” said Vincent Kalkman, an author of the study and a freshwater conservation researcher at the Naturalis Biodiversity Center in Leiden. “It is likely that some of the larger rivers in the south of Turkey, which receive part of their water from melt-water, will decrease in size due to the reduced amount of snow at higher altitude.”
Yet dragonflies and damselflies are expected to gain territory in eastern and northeastern Turkey, the mountain regions of Central Asia and Afghanistan, and the Arabian Peninsula, the study found. Usually an increase in temperature would be “problematic” in such areas, the scientists said, but their modeling suggests that a rise in precipitation will yield benefits, spurring greater biodiversity even in the Arabian peninsula’s southern half.
The Ideal Test Species
Dragonflies and damselflies are viewed as ideal candidates for modeling the biodiversity and health of freshwater ecosystems because of their rapid development, their broad range of species and the ease of identifying them. What is more, all will clearly be affected by climate change.
“No water, no dragonflies,” Kalkman said. “Some dragonflies are capable of surviving periodical droughts, either by being in the egg stage when the habitat runs dry or simply by flying away to a habitat that does have water. However, most species do not fare well with droughts’’—particularly, he noted, those that depend on steadily flowing water.
Leon Marshall, a postdoctoral researcher at the Free University of Brussels and the Naturalis Biodiversity Center who took part in the study, said that dragonflies and damselflies are also more prone to relocate than some other insects.. “A species like dragonflies really have this capability to shift and to follow climate conditions as they change,” he said.
The researchers relied on SDM, or Species Distribution Modeling, to map the areas likely to become suitable for species to inhabit as their environments change. This method draws on historical distribution patterns and topographical details —in the dragonflies and damselflies’ case, soil and rivers— as well as climate projections, Marshall said.
“This gives us a good idea of the fundamental niche of the species,’’ he said, and whether it might shift.
One of the limitations faced by the team, he added, was its inability to factor in how specific water bodies in the regions studied are likely to change in the future, as these predictive models do not yet exist.
In their modeling, the researchers used three different scenarios from the Shared Socioeconomic Pathways, or SSP, framework developed by the United Nations Intergovernmental Panel on Climate Change to help scientists and others with research on climate-related issues like the future of specific species or ecosystems. The three scenarios envisage a range of futures for greenhouse gas emissions, from best to worst, for the periods 2050 to 2070 and 2080 to 2100.
In the best-case scenario, countries achieve their target of net-zero emissions by 2050; in the worst, emissions almost double by that year. A middle scenario projected warming of four degrees Celsius from pre-industrial levels by 2100.
David Buchwalter, a professor at North Carolina State University who studies the impact of contaminants on freshwater insects and environments and was not involved in the study, said he saw its projections as highly plausible. “Temperature profoundly affects the development of ectothermic animals,” he said. “Everything that they do is dictated by environmental temperature.”
A rise in temperatures can affect anything from the number of eggs that dragonflies and damselflies produce to the amount of energy it takes them to maintain their equilibrium, Buchwalter notes. “As you raise the temperature of the air, you raise the temperature of the water,” he said. “As you do that, some species are going to find that the cost of living in terms of what they need to just maintain is too high. Their options are to move upstream where it’s cooler.”
A Double-Edged Sword
While the number of species in some regions will climb as a result of climate patterns, Kalkman cautioned that an increase in biodiversity is not necessarily a good thing when it involves the introduction of nonnative varieties. If regional species migrate to the southern part of the Arabian peninsula as projected, for example, the region could lose some of its character, he said.
He compared the shift to replacing every windmill in his country, the Netherlands, with large office buildings. “The number of buildings remains the same,” Kalkman said, but the nation “loses something of its own character.”
Noting that climate will become the overriding driver of changes in dragonfly and damsel populations in West and Central Asia in coming decades, the researchers urge that their data be used to design a “future-proof” network of nature reserves that include the main freshwater systems in those countries. Governments could create national monitoring systems for freshwater biodiversity to better understand the impact of their policies, they suggest, and share information on a regional scale.
Ultimately, the scientists said, governments could jointly determine whether some species might be able to colonize new habits before their old ones become unlivable.