Extreme weather directs insect and reptile distribution

Future episodes of extreme weather are predicted to lead to mass extinctions in the next century of cold-blooded organisms like insects, spiders and skinks - the so-called ectotherms.

Ectotherms rely on the environment to regulate their body temperature and are therefore more vulnerable to environmental changes.

Using a group of 10 closely related Drosophila species distributed in temperate and tropical regions of the east coast of Australia, Professor Ary Hoffmann and Dr Michael Kearney from the University of Melbourne and Dr Johannes Overgaard from Aarhus University conducted detailed investigations of the flies’ growth and tolerance to thermal extremes.

The researchers determined the temperatures at which the species could develop and reproduce, and their limits of tolerance for hot and cold temperatures. From these results, and the present distribution of the fruit fly species, they then examined whether the present distribution of the species correlated with the temperatures required for growth and reproduction, or whether their distribution was limited by weather extremes.

The results clearly indicated that distribution of the species was defined by their tolerance of unusually hot or cold days. Although temperate species were more able to adapt to changes in average temperature than tropical species, extreme weather posed an equal threat to both.

“The study revealed that extreme temperatures will determine the future distribution of insects, rather than increases in the average temperature,” said Professor Hoffmann.

“With more extreme weather expected in the future due to climate change, our study indicates we are going to see substantial extinctions of some ectothermic species in the next 50 years or so.

“Such losses would not only pose a great threat to biodiversity but also destabilise entire ecosystems,” continued Professor Hoffmann.

Small ectotherms such as bees, worms and spiders provide services that are essential for the health of ecosystems and the viability of agriculture: pollination, pest control and soil turnover.

“The research implies that extreme events - even though they don’t last very long - can have a very large impact on whether a species is going into a decline or not,” Professor Hoffmann said.

The research was published in Global Change Biology.