Climate Change and Boreal Butterflies

A new journal article appearing in Environmental Entomology points to significant changes in the ecology of butterflies in the boreal forests of Manitoba resulting from climate change.

Westwood and Blair, researchers at the University of Winnipeg, studied climate records from 1971-2004 and looked for correlations with population data for 19 common butterfly species.  Climatically,  the mean monthly temperatures in January, September, and December increased significantly, as did the mean temperatures for several concurrent monthly periods. The mean annual temperature increased ~0.05C/yr over the study period. The annual number of frost-free days and degree-day accumulations increased as well.

The researchers looked at date of first appearance, week of peak abundance, and the length of flight period over the 33-yr span, and although adult butterfly response was variable for spring and summer months, 13 of 19 species showed a significant increase in flight period extending longer into the autumn. Flight period extensions increased by over the study period for 13 butterfly species significantly affected by the warming trend. The early autumn and winter months warmed significantly, and butterflies seem to be responding to this warming trend with a change in the length of certain life stages.

Two species, Junonia coenia and Euphydryas phaeton, increased their northerly ranges by ~150 and 70 km, respectively. Warmer autumns and winters may be providing opportunities for range extensions of more southerly butterfly species held at bay by past climatic conditions, the authors say.

“Our results indicate changes in the length of butterfly flight period but not spring activity,” they write.  “Our data support the conclusion that the flight period is extending later into the autumn for many species and that, for some species, peak populations are occurring later in the summer. The climate data analysis points to climate warming in the study area, which is most pronounced in the early autumn and winter, with spring and summer parameters relatively unchanged.”

Other researchers have postulated that increased temperatures may induce species to produce extra generations during a summer, which may or may not fail because of insufficient time for the completion of their life cycles. “This may place species at risk in that they are not in the correct stage to survive the winter.Given the number of butterfly species in this study with extended flight periods, there may be future implications concerning overwintering ability and reproductive synchronization with larval host plants and the presence of adult energy sources at critical egg laying periods,” Westwood and Blair explain.

Read the paper here:  Effect of Global Warming on Butterflies in Manitoba

Full citation:

Effect of Regional Climate Warming on the Phenology of Butterflies in
Boreal Forests in Manitoba, Canada
A. R. WESTWOOD AND D. BLAIR
Environ. Entomol. 39(3): 1122-1133

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