Early snowmelt caused by climate change in the Colorado Rocky Mountains snowballs into two chains of events: a decrease in the number of flowers, which, in turn, decreases available nectar. The result is decline in a population of the Mormon Fritillary butterfly, Speyeria mormonia.
Using long-term data on date of snowmelt, butterfly population sizes and flower numbers at the Rocky Mountain Biological Laboratory, Carol Boggs, a biologist at Stanford University, and colleagues uncovered multiple effects of early snowmelt on the growth rate of an insect population.
"Predicting effects of climate change on organisms' population sizes will be difficult in some cases due to lack of knowledge of the species' biology," said Boggs, lead author of a paper reporting the results online in this week's journal Ecology Letters.
Taking into account the butterfly's life cycle and the factors determining egg production was important to the research.
Butterflies lay eggs (then die) in their first summer; the caterpillars from those eggs over-winter without eating and develop into adults in the second summer.
In laboratory experiments, the amount of nectar a female butterfly ate determined the number of eggs she laid. This suggested that flower availability might be important to changes in population size.
Early snowmelt in the first year leads to lower availability of the butterfly's preferred flower species, a result of newly developing plants being exposed to early-season frosts that kill flower buds.
The ecologists showed that reduced flower--and therefore nectar--availability per butterfly adversely affected butterfly population growth rate.
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