The climate is changing faster than many species can adapt, forcing them to move to new habitats and drastically altering their range, according to new research.
Shifting weather patterns and rising temperatures are rapidly outpacing biological adaptations in certain organisms. Two studies that emerged last week highlight how this has happened in the past and may play out in the future in cold- and warm-blooded animals.
At Indiana University, scientists found that rattlesnakes must move more quickly to remain in favorable environments than they have ever migrated in the past. "It's about two orders of magnitude faster if measured by the number of kilometers a species would have to move," said P. David Polly, a professor in the Department of Geological Sciences at Indiana University.
The rate of climate change is substantially faster than climate shifts observed over the past 5 million to 10 million years, he added. "It's more or less a 'move or die' scenario."
Polly and his co-author A. Michelle Lawing, a doctoral candidate studying biology and geological sciences at Indiana, looked at 11 species of rattlesnakes across North America, tracking where they lived and how much they vary from one another, reconciling their movements with the climate several million years in the past. The researchers published their findings in the PLoS ONE journal.
For Polly and Lawing, rattlesnakes make a good model organism for tracking how species respond to climate change. "We have already assembled quite a lot of data [for rattlesnakes]. Snakes are ectotherms, so their relationship to climate is a lot more direct than, say, mammals, so we know [the climate impacts] in a much more straightforward way," said Polly.
Ectotherms are cold-blooded animals like reptiles that cannot regulate their internal temperature and must depend on their surroundings to heat up or cool off. This makes them more vulnerable to climate shifts and more impelled to move to favorable surroundings.
A cold-blooded outlookIn addition, the snakes in this study, from the genus Crotalus, live largely in areas that experience intermediate climate changes. "When you are closer to the tropics, the effects of climate change are not as strong as they are closer to the poles. Rattlesnakes are somewhere in the middle," explained Polly.
The researchers measured how closely different groups of rattlesnakes were related. "If you know something about the relationships in species to one another and if they had a common ancestor, you can use that to estimate the rate at which they evolved," said Polly. "From the geological record you have data on how fast climate has changed."
After merging the two sets of data, Polly and Lawing mapped how the species' ranges expanded and contracted in 4,000-year increments. After establishing past trends, the scientists extrapolated to the future. "We found that on average, these rattlesnakes have shifted their suitable habitats over the last 320,000 years at a specific rate that is two to three orders of magnitude slower than how fast they will have to move to adapt over the next 90 to 100 years," Lawing said.
Based on these projections, ranges for rattlesnakes will shift by 430 meters to 2.4 kilometers annually. "So basically, their suitable habitat is influenced by climate changes a lot more than it's influenced by evolutionary changes," she said.
The process is a bit different for birds, especially those residing to tropical environments, according to German Forero-Medina, a doctoral student at the Nicholas School of the Environment at Duke University. He explained that since birds can regulate their temperatures, their distribution depends mainly on where they find adequate food and shelter.
As a result, their range shifts are largely a secondary consequence of climate change, but like rattlesnakes, they may not be able to move fast enough.
Tropical birds are also an interesting case study for climate change impacts on ecosystems. According to Forero-Medina, more than half of all birds live at elevations above 1,000 meters, and of those, more than 80 percent live in the tropics.
"When the temperature increases in the tropics, whether you move north or south, there is no change in the temperature," he said, describing how tropical regions generally warm evenly. "The only way to track the change in temperature is to move uphill." As a result, avian temperature responses generally involve moving up or down in elevation rather than stretching or shrinking their ranges over land.
Forero-Medina and his colleagues also published their findings last week in PLoS ONE. The biologists examined bird populations in the Cerros del Sira mountains in Peru, comparing what they found in the 1970s to what they found in 2010.
Birds find it's crowded at the top
Using a weighted mean calculation, the researchers were able to determine a sort of "center of gravity" for a specific bird population, like that of the deep-blue flowerpiercer. The weighted mean is essentially the "average" range for a given species.
The team found that most of the 55 species they studied were moving up into the mountains by an average of 49 meters over the past 40 years of warming. However, the scientists found a significant difference between projected range shifts and how much bird species moved. "They are not moving as much as you would expect to the increase in temperature. The response was about a 33 percent shift of what was expected," said Forero-Medina.
"It is not temperature per se, but [birds] may be tracking the resources as they move uphill. This would explain the lag in the response." In other words, birds are slow to move their nests because they can resist temperature changes, but are traveling to higher elevations to find food or avoid ecological competitors driven by climate change.
Unfortunately for birds and many other organisms, it's crowded at the top: Shifting habitats higher up may increase extinction risks as competition between species increases and viable environments get narrower and eventually run out, said Forero-Medina.
These migrations will be complicated by farming, industry and urbanization. "Human settlement and agriculture has chopped up the landscape, so it's not as easy to for some species to shift as they have in the past. They need help if they're going to do that," said Polly.
However, Lawing said that it's not a hopeless scenario. "Definitely, the warming of the climate is an issue. But once we're on that projected path, there are certain measures that we can help species to get to certain habitats that might be more suitable for them," she said.
According to Lawing, conservationists can use managed relocation to directly move snakes to new areas and establish corridors that will allow organisms to migrate safely to more comfortable homes. Forero-Medina also suggested that conservationists reduce other pressures on migrating species, like pollution, hunting and habitat loss.
Polly and Lawing said that though their current findings are relevant to some other organisms, the scientists' next step is to investigate climate-induced range shifts in mammals and other species. Forero-Medina would also like to quantify extinction risks among birds in the northern Andes mountains.
Using various model animals, the researchers hope to anticipate how wildlife will react as the climate changes and develop strategies to reduce any harm.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500