South American Shifts

One of the core predictions of modern climate science is that rising global temperatures will force plants and animals to shift their ranges toward cooler areas – either toward the poles, or to higher elevations. So far, scientists have indeed documented such shifts in a wide range of species, but few studies have tracked changes in tropical areas. A sweeping new survey of South American plants helps fill that void – and finds troubling indications that climate change is taking hold.

The paucity of tropical studies was “unfortunate given that the majority of all terrestrial species are tropical and the fact that tropical species are predicted to be especially sensitive to climate change,” Kenneth Feeley of Florida International University and the Fairchild Tropical Botanic Garden in Miami writes in Global Change Biology. To close the gap, Feeley combed the world’s herbariums, assembling nearly 500,000 records on when and where botanists had collected 239 species of South American plants. Then, he charted how collecting locations had changed between 1970 and 2009, to see if plants were moving to cooler areas.

He had to be careful, however: Botanists don’t collect plants randomly, but tend to focus on easy to reach areas or particular habitats, potentially skewing the data. Indeed, overall, Feeley found that “virtually all” of the plants “exhibited the predicted cold-ward shifts in their distributions through time. However, for many species these shifts appear to be driven primarily, if not entirely, by changes in where botanists have focused their collection efforts rather than actual changes in geographic distributions.”

Still, after correcting for that bias, 59% of the species exhibited some evidence of moving to cooler climes. Some appeared to be “losers” – expanding into new territory more slowly than they were losing existing range. Others were “winners” – claiming new territory faster than they were losing old. But these “unbalanced shifts” are a cause for concern, Feeley warns, since they could lead to rapid range contractions. Even the winners, he notes, may not be able to keep up with a changing climate for long.

“This is the first study to show evidence for any modern climate-driven species migrations in any lowland tropical species (animal or plant),” Feeley notes. It shows the potential value of using herbarium collections, he adds, although researchers need to be cautious about how they use the data. David Malakoff | January 11, 2012

Source: Feeley, K. (2011) Distributional migrations, expansions, and contractions of tropical plant species as revealed in dated herbarium records. Global Change Biology, n/a-n/a. DOI: 10.1111/j.1365-2486.2011.02602.x 

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