Posts Tagged ‘Ecosystems’

As Weather Warms, Some Animals and Plants Get Smaller

Wednesday, November 2nd, 2011

Whether it’s the polar bear or the petite house sparrow, many of Earth’s species seem to be shrinking in size, a new study reports; its authors believe that is likely a result of global warming.  Other experts disagree, noting that the conclusion goes too far, and that global warming should not be blamed for what could be natural changes.  The research was published in the journal Nature Climate Change. 

The study found that 38 of 85 animal and plant species showed a definite reduction in size over decades, including a type of Scottish sheep that is now five percent smaller than a quarter century ago.  Those studies examined species over different time periods and in diverse numbers.  According to the study, species that are getting smaller include cotton, corn, strawberries, bay scallops, shrimp, crayfish, carp, Atlantic salmon, herring, frogs, toads, iguanas, hooded robins, red-billed gulls, California squirrels, lynx and wood rats.  The study notes that the house sparrow’s weight has dropped by one-seventh between 1950 and 1990.  A bird known as the graceful warbler showed a 26 percent weight loss during the same timeframe.

“There is a trend in a number of organisms across the board from plants to big vertebrates getting smaller,” said study co-author Jennifer Sheridan, a biology researcher at the University of Alabama.  “The theory is as things get warmer they don’t need to grow as large.”  The majority of these animals are cold-blooded, so the warmer the weather the faster their metabolism and the more calories they burn, according to Sheridan.  A biological law, called Bergmann’s rule, says that as the weather gets colder, animals get bigger.  This is the unwritten flip side of it, Sheridan said.

Yoram Yom-Tov, a zoologist at Tel Aviv University whose studies Sheridan used in her research, agreed that many species are shrinking, and noted that global warming isn’t the only reason.  “Changes in body size are a normal phenomenon,” Yom-Tov said.  “When conditions are favorable, they increase in size or reproduce at higher rates, and when conditions are deteriorating, they do the opposite.  I think that most species will adapt to climate change and survive.  No need for alarm.”

Many scientists believe that the study confirms that climate change is shrinking many plant and animal species and is likely to have a negative impact on human nutrition in the future.  Warmer temperatures and increasing variability in rainfall are affecting the size of all species in the ecosystem from microscopic sea organisms to land-based predators.  “Our study suggests that ectotherms (cold-blooded animals like toads, turtles, and snakes that rely on environmental heat sources) are already changing a lot,” said David Bickford from the National University of Singapore and the study’s co-author.  “What was most surprising to me was that it was such a uniform signal across all these different organisms,” Bickford said.

Sheridan and Bickford examined fossil records, which they found to be clear-cut: past eras of rising temperatures saw both marine and land organisms becoming progressively smaller.  During a time of warming 55 million years ago — often viewed as an analogue for current climate change — beetles, bees, spiders, wasps and ants shrank by 50 to 75 percent over a period of several thousand years.  Mammals such as squirrels and wood rats also shrank by about 40 percent.

Because warming is occurring at unprecedented rates, “Many organisms may not respond or adapt quickly enough”, especially those with long generation times, according to Sheridan and Bickford.  “We do not yet know the exact mechanisms involved, or why some organisms are getting smaller while others are unaffected.  Until we understand more, we could be risking negative consequences that we can’t yet quantify.”

Stanford biologist Terry Root, an expert in climate change, said the study’s conclusions “seem kind of far-fetched.”

Writing for the Nature.com news blog,  Susan Young says that “Temperature-linked changes in precipitation also affect the size of organisms.  Higher temperatures lead to drier environments, and Sheridan and Bickford suggest that reductions in size will be most pronounced in areas where global warming causes reduced precipitation as well.  Tropical trees, toads and mammals are known to grow slower during drought years and under experimental drying conditions.  Other environmental changes will also affect life on earth.  As the atmosphere loads up with carbon dioxide, so do the planet’s oceans, which raises the acidity of the water.  Higher acidity reduces the rate at which organisms like corals and oysters can form their shells.  The result, the authors say, is that these ocean creatures shrink.  The growth of red algae and phytoplankton are also hampered by the lower pH.  The authors note that the warming-shrinking trend does not apply to every organism, such as those with longer generation times or some at higher latitudes.  This variation exacerbates the problem.  If all organisms in a given ecosystem shrank on scale with one another, smaller predators could eat smaller prey that eat smaller plants, and all would be fed.  But that is not what ecologists are observing.  Organisms change with variable intensity depending on their lineage, size and location, and ecosystems are likely to be thrown off balance.”

Temperatures Rising in America’s Freshwater Lakes

Wednesday, August 10th, 2011

The waters of the Great Lakes are warmer than usual this year, prompting scientists to worry that this may not be a good thing.  All five Great Lakes have been at or near record-high temperatures compared with the 30 years when such measurements have been taken.  The bad news is that there’s still a month remaining before the lakes typically reach their warmest temperatures.  Jay Austin, a physics professor at the Large Lakes Observatory in Duluth, MN, says the water is warmer because last winter there was little or no ice cover to reflect sunlight.   Scientists are unsure if it’s a blip or the new normal.  A warmer Lake Superior might be a plus for the tourism industry, but it might be bad for fishing, wildlife habitat and water levels.

“Swimmers are enjoying it,” said Al Oleksuik, who lives near the Welland River in Chippewa.  “I notice a difference here.  (The water is 24 C). It usually doesn’t hit that until mid-August. I have a feeling we’re headed towards (26 C), which is extremely warm.”  Austin said the lake is 5 to 7 C warmer than it usually is in mid-July, while the Great Lakes in general are running 2 to 7 C warmer.  “It’s going to set records, or come close, depending on where you are,” he said.

Writing in Chimes, a publication of Grand Rapids-based Calvin College, Geneva Langeland says that “Lake Michigan is warming up?  Swimmers who brave the lake’s often frigid waters might beg to differ.  But Lake Michigan’s waves aren’t alone in their slight temperature uptick; NASA satellite data suggest that lake temperatures worldwide have risen in the last 25 years, most likely as a result of global climate change.  Phillip Schneider and Simon Hook, researchers at NASA’s Jet Propulsion Laboratory in California, departed from the typical strategy of measuring global warming trends by gauging air temperatures near Earth’s surface.  Instead, the study, published in the 2010 issue of Geophysical Research Letters, used infrared satellite imagery to track changing surface temperatures in 167 large lakes splashed across the globe — including our very own Great Lakes.  The satellite data suggest that, over the past 25 years, water temperatures in large lakes have risen between .81 and 1.8 degrees Fahrenheit per decade.  These shifting temperatures varied widely among continents and hemispheres.”

According to Langeland, “Schneider and Hook noted the greatest change in northern Europe; in general, the loftier latitudes of the Northern Hemisphere consistently reported the largest temperature upticks.  The Great Lakes land squarely in that northern region.  Huron, Superior, Michigan, Erie and Ontario together comprise the world’s largest freshwater lake system.  It should come as no surprise that the ‘Big Five’ were valuable players in this study.  In fact, the Great Lakes host nine temperature-gauging buoys that were vital in verifying NASA’s satellite temperature readings.  As Schneider said, ‘The results have implications for lake ecosystems, which can be adversely affected by even small water temperature changes.’  A degree or two might be imperceptible to us, but this tiny change can have surprising repercussions.  Every organism thrives within a particular temperature range.  Altering a habitat’s air and water temperatures even slightly will kill off some creatures while allowing others to unexpectedly thrive.”

Lakes in the American West are experiencing similarly increasing temperatures.  Warming that meets statistical significance was found in Lake Tahoe along the California-Nevada border; Pyramid Lake in Nevada; and the Great Salt Lake in Utah, which were warming at a rate of more than one degree Fahrenheit per decade.  “One of the things we want to do in the future is compare these results with what the climate models predict in the region,” Hook said.  “Measuring a model’s performance in replicating changes of the recent past gives scientists a way to test the accuracy of the models being used to project future conditions.”

“Our analysis provides a new, independent data source for assessing the impact of climate change over land around the world,” Schneider said. “The results have implications for lake ecosystems, which can be adversely affected by even small water temperature changes.”