There is overwhelming evidence that many species have shifted the geographical ranges they live in over recent decades, with some actually becoming more widespread. However, adverse effects of climate change could still await these species, say University of Wyoming’s Daniel Doak and William Morris at Duke University in Durham, North Carolina.
Their research shows competing influences are holding the southern range limit of two Arctic and alpine plants in place, while warming forces the northern limit further north. However, their temperature-driven spread may ultimately prove short-lived, Doak warns. “Up to a point we may see little effect of warming for many organisms,” he says. “But past a climatic tipping point, the balance of opposing effects of warming will likely cease, leading to subsequent rapid declines in populations.”
The conclusions are based on observations Doak and Morris recorded during a six year study of the tundra plants moss campion and alpine bistort in four locations in North America. They studied the averages and year-to-year changes in “vital rates” of these plants: survival, growth and reproduction. The researchers were particularly interested in what was happening at the southernmost, warmest, regions, where there has been little change in where plants can be found.
Having divided the plants into classes by size, they discovered that the southern boundaries was where one or more class in both species had its lowest average survival rate. Reproduction was equally challenged, with no new alpine bistorts establishing themselves at the southernmost end of any of the four study sites in two years of the study. Both of these situations would suggest that southern plants might soon die out. “But in most years these effects are balanced by plants in the south growing more rapidly, so that populations there are no less stable than those in the north,” Doak explains. Writing in leading scientific journal Nature on Thursday, Doak and Morris suggest this acceleration is possibly due to longer, warmer growing seasons.
“With warming from low to moderate temperatures most vital rates increase; across moderate temperatures some rates increase, some are stable and some decrease; and from moderate to high temperatures most rates decrease,” they write. “Continued warming can be expected to eventually result in deterioration of most vital rates, potentially shifting a population that is stable owing to contradictory changes at moderate temperatures into rapid decline once a tipping point has been passed.” As it’s not currently known which species will pass this tipping point, more research is needed to find this out, Doak and Morris say.