Early Snow Melts Mean Fewer Butterflies
March 16, 2012

Early Snow Melts Mean Fewer Butterflies

Long-term data suggests that an early snow melt in the Rocky Mountains starts a chain reaction that ends with decreased butterfly population. Biologists from Stanford University conducted the research on the Mormon Fritillary butterfly at Rocky Mountain Biological Laboratory (RMBL).

According to the data, when snow melts early in the Rocky Mountains, fewer flowers bloom; When fewer flowers bloom, nectar becomes less available. This, in turn, means that fewer butterflies are born.

This kind of research is being conducted to understand the way environments and ecosystems work together.

“This suggests that predicting effects of climate change on organisms´ population sizes will be difficult in some cases due to lack of knowledge of the species´ biology,” noted Dr. Carol Boggs, professor in the department of biology at Stanford University and lead author on the study.

In order to conduct the research, the biologists had to understand the full life cycle of the butterfly.

In their first summer, butterflies lay their eggs and then die. From those eggs are born caterpillars who over-winter without eating. During the second summer these caterpillars mature into adult butterflies.

According to Boggs´ research, the amount of nectar the butterflies ate directly determined the number of eggs she laid. Therefore, when fewer flowers are available, fewer butterfly eggs are laid.

As snow melts early in the Rocky Mountains, the butterflies preferred flower species are being exposed to early frosts, thereby killing the young buds.

From this data, the biologists deduced that flower-and nectar-availability directly affected butterfly population.

When there is an early snowmelt for consecutive years, the decrease in butterfly population is pronounced, in some cases by as much as four-fifths.

“It is very unusual for research to uncover such a simple mechanism that can explain almost all of the variation in growth rate of an insect population”, said Dr. David Inouye, professor of biology at the University of Maryland and co-author of the study.

While this seems like a simple observation with simple and predictable results, the scientists say they are surprised to see an insect with such a short life span be affected by this kind of climate change.

“One climate parameter can have multiple effects on an organism´s population growth,” Dr. Boggs stated. “This was not previously recognized for species such as butterflies that live for only one year. We already can predict that this coming summer will be a difficult one for the butterflies, because the very low snowpack in the mountains this winter makes it likely that there will be significant frost damage.”

As studies like this continue, scientists hope to learn more about specific ecologies and how every element works together as one.

“Long-term studies such as ours are important to understanding the ℠ecology of place´ and the effects of weather and possible climate change on population numbers,” commented Dr. Inouye. “Research of this nature is critical to assessing the broader effects of weather on an ever-changing earth, and field stations such as RMBL, by facilitating longer-term, longitudinal studies, are an invaluable asset in this regard.”

The results of this study, which was funded by the National Science Foundation´s Division of Environmental Biology, were published online in this week´s journal Ecology Letters.


Image Caption: A Mormon Fritillary butterfly feeding on an aspen fleabane daisy, a main nectar source. Credit: Carol Boggs