Extreme weather decides distribution of insects

Christina Troelsen and Johannes Overgaard in a press release from the University of Aarhus (Denmark): As climate change is progressing, the temperature of our planet increases. This is particularly important for the large group of animals that are cold-blooded (ectothermic), including insects. Their body temperature is ultimately determined by the ambient temperature, and the same therefore applies to the speed and efficiency of their vital biological processes.

But is it changes in average temperature or frequency of extreme temperature conditions that have the greatest impact on species distribution? This was the questions that a group of Danish and Australian researchers decided to examine in a number of insect species. ... The results demonstrate that it is especially the extreme temperature events that define the distribution of both tropical and temperate species. Thus climate change affects ectotermic animals primarily because more periods of extreme weather are expected in the future.

The researchers examined 10 fruit fly species of the genus Drosophila adapted to tropical and temperate regions of Australia. First they examined the temperatures for which the species can sustain growth and reproduction, and then they found the boundaries of tolerance for hot and cold temperatures. “This is the first time ever where we have been able to compare the effects of extremes and changes in average conditions in a rigorous manner across a group of species”, mentions Ary Hoffmann.

 Based on this knowledge and knowledge of the present distribution of the 10 species they then examined if distribution was correlated to the temperatures required for growth and reproduction or rather limited by their tolerance to extreme temperature conditions. "The answer was unambiguous: it is the species' tolerance to very cold or hot days that define their present distribution," says Johannes Overgaard.

It is therefore the extreme weather events, such as heat waves or extremely cold conditions, which costs the insects their life, not an increase in average temperature. With this information in hand, the researchers could then model how distributions are expected to change if climate change continues for the next 100 years....

A fruit fly, shot by Sanja565658, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license