Dragonflies As Climate Change Prognosticators

Alan McStravick for redOrbit.com – Your Universe Online

Scientists exploring the speed and scope of climate change have often looked at flora and fauna in a particular region as a major indicator. Many of these plant species will adjust their inner clock leading to earlier and earlier periods of bloom. However, not all biological life forms are able to adjust to a change in climate so quickly, according to a recent report published by the European Environmental Agency. It is for this reason studies have also focused on climate sensitive communities of insects. Monitoring insects and other climate sensitive species could be crucial in helping researchers to develop indicators for climate change effects on a region’s biodiversity. The recognition of these indicators will play an important role in the formation of policies to protect life most affected by a change in climate.

A study published last year examined populations of North American butterflies. The authors of that study acknowledged that the collection of data needed to document shifts in climate change is not as prevalent as they are in Europe. One primary reason noted is the commitment on the part of European governments to conduct long-term survey data collection studies.

Last year’s study, however, reviewed nearly 20,000 independent butterfly surveys conducted between 1992 and 2010. These independent surveys were conducted by amateur naturalists in the state of Massachusetts. The study noted Massachusetts is a prime region for study as it is located at the convergence of the northern and southern bioclimatic zones in eastern North America. Their findings showed population trajectories for the northern range limit species were on the increase. Conversely, almost every southern range limit species experienced a downward trajectory for their overall populations. Their findings suggest, they say, there is a major, climate-induced shift of North American butterflies, characterized by northward expansions of warm-adapted and retreat of cold-adapted species.

A new study supports the findings published last year. German scientists found the regional composition of butterfly and dragonfly communities, like those reported in Massachusetts, have undergone a significant change in the last decade. This most recent study, entitled “Climate Change and Biodiversity” is set to be formally published within two months time. “We know a great deal from modeling studies [about climate impact on biodiversity], but we know to a lesser extent what really happens,” stated Maik Denner, co-author of the study. Denner, a nature conservation scientist, works for the State Office for the Environment, Agriculture and Geology in Dresden, Germany.

Researchers for this study utilized already established biodiversity monitoring programs, like those in Switzerland, the UK and in Germany’s North Rhine-Westphalia region. Specifically, the scientists culled over species distribution and monitoring data in order to calculate the so-called community temperature index (CTI) of butterflies and, in a first for climate change research, the populations of local dragonflies.

The team was able to note there was a direct correlation between changes in the CTI over time and changing temperature. This correlation was indicative of shifts within a species regional composition in a particular community.

In the present study, which observed an increase in CTI, the researchers documented a marked increase in the proportion of warm-temperature dwellers coupled with a significant decrease in the proportion of cold-temperature dwellers, according to Denner. Important to note, however, is that the CTI of both of these communities did not change to the same extent as the physical temperature did. This, according to the research team, suggests the observed shifts were not able to compensate for the observed increase in temperature.

According to Vincent Devictor, a research scientist at the Institute of Evolutionary Sciences in Montpellier, France, “If [the CTI] increases, you know that it is a direct biodiversity response to climate change.” Devictor’s work in this field includes having led a previous study where species from seven European nations were monitored. Devictor, in light of this most recent study’s results, goes on to state, “…policy makers can read the intensity of climate change using this simple metric.” Devictor’s earlier work based on CTI calculation showed European butterfly and bird communities were already shifting drastically northward over the previous two decades. Despite this northerly exodus, neither of the populations was shifting fast enough to keep pace with increasing temperatures.

While North American and European researchers maintain faith in their findings, the results are not without their detractors. Many experts have doubt that temperature effects alone can be behind the changes in the butterfly and dragonfly communities. “In principle, the CTI is a promising indicator concept,” states Ulrich Sukopp, a monitoring expert employed by the Federal Agency for Nature Conservation in Bonn, Germany. Sukopp works on establishing climate change indicators. He goes on to discuss how a direct correlation between temperature and CTI has yet to be clearly demonstrated. In aid of establishing that correlation, he comments that more and better monitoring data is still needed.

Also joining the call for the development of more intelligently designed monitoring programs is Ingolf Kühn, coordinator of the EU sponsored project, Minimisation of and Adaptation to Climate Change Impacts on Biodiversity (MACIS) and senior scientist at the department of Community Ecology at the Helmholz Centre for Environmental Research in Halle, Germany. Kühn comments on the application of the CTI in smaller regions and calls it “problematic” as changes in land use can have a direct affect on the index. “It’s more robust when applied to larger regions.” MACIS was instrumental in the publication of a 2009 European Commission white paper entitled “Adapting to climate change: Towards a European framework for action.”

While the correlation of these two major events has yet to be definitively demonstrated, it is clear there is something behind the mass migration of both populations of butterflies and dragonflies. With continued dedicated study, we may soon know the exact cause.

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