Nearly 230 Society monitors recorded species numbers from the first week of April through the first week of November. Their data was compared with temperature records.
Temperatures were taken from the nearest National Oceanic and Atmospheric Administration meteorological stations, which avoid the warming effects of urbanization.
Sites in southern Ohio ranged 2 to 3 degrees Celsius warmer than northern sites on a given day. That difference reflects the amount of warming climate change models predict for the Midwest later this century, enabling the researchers to see how the change may alter butterfly lifecycles.
The lepidopterists' records showed that butterflies generally emerged up to three weeks earlier and reached peak numbers sooner in southern Ohio than mid- and northern Ohio.
Biologists believe that advancing their lifecycle events a couple of weeks enables butterflies to take advantage of earlier flowering induced by warmer temperatures. The bigger payoff is a species may add another generation in a year, increasing its population and ability to compete.
Urban heat tips pattern
To estimate the heat from urbanization, researchers calculated the percent of impervious surface within 1 kilometer of each monitoring site, using the National Land Cover Database. Research by others shows the percentage of impervious surface is correlated with specific increases in surface and air temperatures.
When this heat was added to the already warmer temperatures in greater Cincinnati and Dayton, seven species delayed their initial appearances. Three of them, plus one other species, delayed their peak numbers.
"Butterflies need warmth from the environment to develop," Ries said. "As their environment gets warmer, they have more and more energy but at ex
|Contact: Kevin Mayhood|
Case Western Reserve University