"But in most years," says Doak, "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."
The opposing trends mean that under current conditions, even across the huge range of conditions Morris and Doak studied, populations of these plants are doing equally well across 30 degrees of latitude--one-third the distance from the equator to the north pole.
However, the researchers' results don't indicate that these plants, or other species, will be unaffected by warming conditions.
By looking at the performance of individual plants in particularly hot and cold years, they found that the compensatory effects across moderately cold to moderately warm years (lower survival balanced by more rapid growth) will not hold up with increased warming.
Instead, in the warmest years at all study sites, both survival and growth of the plants fell.
"Up to a point," says Doak, "we may see little effect of warming for many organisms. But past a climatic tipping point, the balance of opposing effects of warming will likely cease, leading to subsequent rapid declines in populations."
While this tipping point will be different for each species, responses of natural populations to gradual shifts in climate will not necessarily in turn be gradual.
"We shouldn't interpret a lack of ecological response to past warming to mean that little or no effects are likely in the future," says Doak.
The researchers' work also points to a methodology with which to better understand and predict how climate effects on one species will combine to create overall population-wide effects.
"A key part of this approach is the need for long-term studies so we can observe and use the rare years with extreme climates to anticipate what the average future climate will bring," Doak says.
|Contact: Cheryl Dybas|
National Science Foundation