Butterfly Range Shifts Are A Sign Of Global Warming

Last month, after 18 years of observation and nearly 20,000 surveys, a very interesting study was published in Nature Climate Change about the effects global warming has on Massachusetts’s butterflies. Conducted by amateur scientists of the Massachusetts Butterfly Club, the study supported the hypothesis that global warming is the culprit when it comes to the changes in the “distribution and abundance” of butterfly populations on the Northeast Coast. As the temperature is rising, populations of warm-adapted butterflies are increasing in size and moving farther north, whereas populations of cold-adapted butterflies in Massachusetts are decreasing in size.

Over the past 100 years, the temperature of Massachusetts has risen 3.6 degrees Fahrenheit. Although this may not seem like a huge increase, the effects it has on northern butterflies can be deadly. Of the 21 northern butterfly species reported in the study, a whopping 17 were in decline. That is 81 percent! One particular Massachusetts butterfly population of the species Speyeria atlantis, for example, declined by 90% in just 17 years.

Yet, the southern butterfly populations are experiencing the exact opposite effect; instead of decreasing in population size, they are actually growing in size and expanding into northern states. It was noted that the 12 southern species of butterflies that were very rare in the north before 1990 were growing significantly. In a way, these growing southern populations are invasive species, in that they are moving into the northern butterflies’ territory, and while the northern butterflies are dying, the southern butterflies are prospering and “taking over.”

One very interesting point made in the article was how global warming is affecting many species of butterfly that overwinter as larvae. If the summer, fall and, winter are warmer due to global warming, the snow melts at a quicker rate and the butterflies that overwinter their eggs might encounter a lack of water; this can lead to dehydration. Also, global warming may cause plants to grow earlier in the year, which can lead to the shading of butterfly larval. This, in turn, may slow larval growth in the species that hatch in the spring. To me, this was amazing; I would never have concluded this on my own.

As an environmental advocate and the writer of an “anti-global warming” blog, this is a very interesting topic for me. Since the temperatures of most places on Earth are warming up, it is no surprise that the southern butterfly populations are able to survive in a wider variety of places. If the Massachusetts environment is as warm as their original habitat in the south, why not inhabit both?

But, my concern, as well as the concern of many scientists, is the future of the northern butterfly populations. They are adapted to cooler temperatures, and with the Massachusetts temperature rising, they are at risk. My only question is: why don’t they move farther north, just as the southern butterflies did? If they move to a place that is higher north, will they be able to survive better? I am very fascinated by this, but at the same time, upset. The damages we are causing due to our emission of greenhouse gases and pollution is very detrimental to wildlife, so we really need to step up and work together to make this world a better place, before it is too late.

What are your reactions toward this study? The scientists made it very clear in the article that habitat change, landscape change, and host-plant rarity did not seem like probable causes to the changes in the butterfly communities, and that climate change was the most plausible explanation. Do you think that there are other factors affecting this population shift? Is it too late to step in and save some of these northern butterfly populations? One southern species of butterfly, called the Frosted Elfin, receives protection from the state of Massachusetts, even though it has increased by 1000 percent since 1992, while many northern species in decline still receive no protection. When I heard this, I was shocked and upset. What are your feelings toward this? Please comment and share your thoughts below.

Photo Credit: Ken Slade (via Flickr)

Sources:

Greg A. Breed, Elizabeth E. Crone, & Sharon Stichter “Climate-driven changes in northeastern US butterfly communities” Nature Climate Change August 19, 2012

Jason McLure “Massachusetts Butterfly Populations' Shifting Likely Due To Climate Change, Study Shows” Huffington Post August 22, 2012