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| Mormon Fritillary butterflies mating in the Rocky Mountains: will this population survive? (Credit: National Park Service) |
By ScienceDaily, March 16, 2012
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.
Early snowmelt in
the second year of the butterfly life cycle worsened the effect, probably
through direct killing of caterpillars during early-season frosts.
The combined
effects of snowmelt in the two consecutive years explained more than
four-fifths of the variation in population growth rate.
"Because
species in natural communities are interconnected, the effects of climate
change on any single species can easily be underestimated," said Saran
Twombly, program director in the National Science Foundation's Division of
Environmental Biology, which funded the research.
"This study
combines long-term, data models, and an understanding of species interactions
to underscore the complex effects climate change has on natural
populations."
"It's very
unusual for research to uncover a simple mechanism that can explain almost all
the variation in growth rate of an insect population," said David Inouye,
a biologist at the University of Maryland and co-author of the paper.
Indeed, "one
climate parameter can have multiple effects on an organism's population
growth," Boggs said. "This was previously not recognized for species
such as butterflies that live for only one year.
"We can already
predict that this coming summer will be a difficult one for the
butterflies," she said, "because the very low snowpack in the
mountains this winter makes it likely that there will be significant frost
damage."
"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,"
said Inouye.
"This research
is critical to assessing the broader effects of weather on an ever-changing
Earth," he said. "By facilitating long-term studies, field stations
such as the Rocky Mountain Biological Laboratory are an invaluable asset."
Story Source:
The above story is reprinted from materials provided by National Science Foundation.Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Journal Reference:
- Carol L. Boggs, David W. Inouye. A single climate driver has direct and indirect effects on insect population dynamics. Ecology Letters, 2012; DOI: 10.1111/j.1461-0248.2012.01766.x
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