Canadian beetles are shrinking because of climate change

The beetles

It is expected that organisms will respond to climate change in three ways; by moving to new habitats, by changing the timing of their life changes, or by shrinking. Researchers, led by Dr. Michelle Tsang, at the University of British Columbia wanted to find out how various species of common ground beetle found in the province were responding. They accessed the university's own collection of specimens dating back over 100 years for the answer.    

The study

The researchers measured many different species of beetle to see if they had changed in size over the past 45 years.  The number 45 is significant only because the collection had all eight of the species studied going back that number of years. The study focused on two areas of the province; the lower mainland and the Okanagan Valley. They then compiled climate data for these two area over the same number of years. They found that the lower mainland has seen a 1.6 C increase in temperature and the Okanagan a 2.25 C increase, both autumn averages. Depending on the species, the beetles shrunk in size ranging from 40 percent to 16 percent, for an average of about 20 percent across all species.       

• Salamanders Shrink as the Climate Warms
• Climate Change is Shrinking Arctic Butterflies
• Shrinking Coyotes

Why shrink?

Shrinking as a response to climate change was already known in some butterflies, bees and other organisms.  Still, scientists in this study were surprised by the amount of shrinkage in the beetles. The mechanism is that higher temperatures increase the rate of metabolism. This results in the beetle going through life stages faster and reaching adulthood earlier without having to add body mass. They believe that the beetles are near a point at which they cannot shrink any more even as their habitat continues to warm.      
 
Paper in the Journal of Animal Ecology