A Mormon fritillary butterfly visiting an aspen fleabane daisy. This flower is the primary nectar source for the butterflies, which need the nectar to make eggs to produce the next generation of butterflies.
Early snowmelt in the Colorado Rocky Mountains may drive down the population of Mormon fritillary butterflies by reducing their favored nectar supply and killing off caterpillars that die during early-season frosts.
Stanford researchers found that early snowmelt for two consecutive years explained more than four-fifths of the observed variation in population growth rate, according to a study recently published in the journal Ecology Letters .
"We already can predict that this coming summer will be difficult for the butterflies, because the very low snowpack in the mountains this winter makes it likely that there will an early snowmelt and significant frost damage," said biology Professor Carol Boggs , lead author of the study.
Boggs said the blow to the butterfly population can be explained by looking at the insect’s lifecycle and the factors determining egg production.
"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," Boggs said.
Butterflies lay eggs and then die in the first summer. The eggs become caterpillars that overwinter without eating and develop into adults in the second summer.
Laboratory experiments showed that the amount of nectar a female eats determines the number of eggs she will lay, suggesting that flower availability per female might be important to changes in population size.
To test this hypothesis, researchers at the Rocky Mountain Biological Laboratory (RMBL) in Crested Butte, Colo., collected long-term data on the Mormon fritillary, or Speyeria mormonia, a common North American butterfly.
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