California’s butterfly populations are suffering from the combination of a warming climate and increased land development, according to a new analysis from scientists at UC Davis.

The study, scheduled to be published online this week in the journal Proceedings of the National Academy of Sciences, draws from butterfly expert Arthur Shapiro’s database of more than three decades of observations of 159 species from 10 sites in the Sierra Nevada at varying elevations, from sea level to tree line.

The data shows that over the last three decades butterfly species diversity declined at half of the sites, with the most severe reductions occurring at the lowest elevations, where habitat destruction is greatest.  The sites in the middle range showed evidence of habitats shifting upslope, as lower elevation butterflies began appearing at higher elevations.  The only site studied where butterfly biodiversity and abundance has increased is at the highest elevation site, at 2,400-2,775 meters.

“These patterns are quite consistent with other studies on a variety of organisms,” said Shapiro.  “The trend is for organisms to seek the climate to which they are adapted. So if it’s getting warmer, that means you go north, or you go up.”

While the population shifts appear consistent with warming temperatures (Both average maximum temperatures and average daily minimum temperatures increased across the majority of the sites), the study finds that warming alone is not enough to account for the loss of biodiversity at low and middle elevations.  Researchers analyzed county land use data at the sites, and found that it correlates with the butterfly population data.  The authors propose that habitat destruction due to urban and suburban development is most likely the leading cause of butterfly population deterioration at the lower elevation sites.

Citing pressures from human development as the main cause for species loss, the United Nations declared 2010 to be the International Year of Biodiversity.  At the Johannesburg summit of 2002,  governments agreed to achieve “significant reduction” in the rate of biological diversity loss by 2010, but according to the BBC, conservation organizations are acknowledging that this target is not going to be met, and that, in fact, the problem may be worsening.