Climate change effects revealed through bugs collected for 18 years on the rooftop of the Copenhagen Zoological Museum

A study published on November 2 in the Journal of Animal Ecology has implications for our understanding of climate change and how insects adapt to changes in their habitat and surrounding environment. For the past 18 years, from 1992 to 2009, researchers from the Center for GeoGenetics and the Center for Macroecology, Evolution and Climate have collected, using a light trap on the rooftop of the Copenhagen Zoological Museum, over 1543 different species of moths and beetles totaling to more than 250,000 specimens. Through this monitoring, researchers have discovered that the insect community has undergone significant changes during this period.

“As the temperature rises, we see a corresponding change in the insect community, specifically for the resource specialists – the insects that feed on only one species of plant,” says one of the lead authors, postdoc Philip Francis Thomsen of the Center for GeoGenetics, University of Copenhagen. “Earlier studies have confirmed that specialist species also respond rapidly to destruction of their habitats, so we are dealing with a very sensitive group of animals.”

One example of this sensitivity to change can be found in the two resource specialist species of beetle, the nut weevil (Curculio nucum) which eats hazelnuts and lives further north and the acorn weevil (Curculio glandium) which eats acorns and lives further south. Halfway through the study, the inventories showed something interesting about these species. There were no longer nut weevils in the light traps, but instead acorn weevils, suggesting northward movement due to slowly rising temperatures.

Peter Søgaard Jørgensen, another of the lead authors and Phd at the Center for Macroecology, Evolution and Climate (currently a postdoc at the Royal Swedish Academy of Sciences), explains these results: “We are likely to lose some specialist species as they retreat north, but more new specialist species will arrive from the south. This trend is theoretically expected but extremely rare to confirm with observations across this many species. Insects are often over-looked and under-prioritized for long term studies.”

Ole Karsholt and Jan Pedersen – also co-authors – were the two men who, for 18 years, were in charge of light trap maintenance and insect collection and documentation. The insects that they collected represent 42% of the butterflies and 12% of the beetles known to live in Denmark, but interestingly, they also found two species of beetles and seven species of moths that are not native to Denmark and have never been registered here before.

“Some insects are very mobile and only eat as larvae. It is therefore not unusual to find them further from their habitats as adults. However, it is an impressive diversity of species registered. Even though the study is limited to one site, there is no reason to believe that the trend we see here would be different at other sites” says Peter Søgaard Jørgensen.

Finally, this study reveals the immense impact that a seemingly small temperature change can have on the these insect species. Philip Francis Thomsen says, “There is an increase of 0.39 degrees, but this is enough to affect the insects significantly. At the same time, we show that this type of study can be used to measure the effects of global warming – it has not been done this way before – and in addition, the work value of continuously monitoring nature.”

“The results confirm that climate change is impacting biodiversity right now. It is not something that will happen far into the future or only if we reach a two degree temperature increase,” says Peter Søgaard Jørgensen.

The Center for GeoGenetics with center leader Eske Willerslev and the Center for Macroecology, Evolution and Climate with center leader Carsten Rahbek are funded by the Danish National Research Foundation.