Warming World May Mean Smaller Animals

Andrea Thompson, livescience.com 20 Jul 09;

As Earth's climate continues to warm, life might become the province of the small, a new study suggests.

Climate change has already had documented effects on species living across the globe, from polar bears in the Arctic to coral reefs in the tropical seas. While some changes are specific to certain types of animals, others seem to be more universal.

Two such ecological changes that have been noted and predicted are the shift of species' ranges to higher altitudes and latitudes to keep within their temperature comfort zones and the shift in the timing of key events in the life cycle of organisms - for example, the flowering of plants or the migration of birds.

A third change can now be added to that list: As temperatures rise, organisms get smaller, from the scale of whole communities down to the individual.

This relationship was known to exist in nature, with warmer environments tending to be dominated by smaller-sized species, said study leader Martin Daufresne of Cemagref Aix-en-Provence (a French governmental research institute). But what Daufresne and his colleagues aimed to do with their study was "was to test if this known relationship in ecology was working for climate change," he said.

They found that it's working.

The results of their research are detailed in the July 20 issue of the journal Proceedings of the National Academy of Sciences.

Shift to the small

This relationship between warmer environments and smaller size works at three different levels in a given biological community: "Being small could mean that you are belonging to a small-sized species; but it could also mean that you are younger, or that you are small for your age," Daufresne explained.

He and his colleagues used long-term surveys to look at these measures for several different aquatic communities that encompassed a variety of organisms (including bacteria, phytoplankton and fish) living in a variety of environments (large rivers, streams and salt water).

The researchers found that, on average, these communities did in fact get smaller as temperatures rose in their environments over time.

For communities of fish in large French rivers, for example, the team observed "a decrease on average of something like more than 60 percent of the mean size at the community scale," during the span of about two decades, Daufresne told LiveScience. This decrease was due to a combination of an increase in the proportion of small-sized species, an increase in proportion of juveniles, and a decrease in size at a given age among individuals within a species.

What exactly is behind this shift isn't clear yet and will require further study, Daufresne said. "Since we observe this decrease at the different scales, it's a bit difficult to find a common trigger - maybe there are several triggers, or maybe just one," he said.

What is clear though, "is that it's something which seems to happen everywhere," which supports global warming's role, Daufresne said. "The fact that we observe this common pattern among different systems and among different kinds of organisms means that there is a real effect of the global warming on size."

Sheep and consequences

More research will be needed to see if this same relationship holds for other species and environments, particularly land-based creatures and warm-blooded animals. One recent study in the journal Science suggests that global warming might be causing the same effect in Scottish sheep, as the woolly beasts seem to have gotten smaller with milder winters over the last few decades.

Whether or not these changes are adaptive to the animals undergoing them is uncertain and something Daufresne hopes to resolve with further research.

Daufresne and his colleagues also want to look into just what the cascading effects of this shrinking might be to communities. One potential way the size change could reverberate would be through the food chain.

"The size of the species is related generally to the position within the food chain, for example, the bigger you are, the [higher up] you are in the food chain," Daufresne said. With sizes shifting to the smaller end of the spectrum, "maybe the upper trophic level could be more sensitive to climate change," which could affect the relationships between predator and prey, he added.

The effect could also be bigger at higher latitudes where warming is expected to be starker, Daufresne said.

Fish are shrinking in response to global warming: study
Yahoo News 20 Jul 09;

CHICAGO (AFP) – Fish have lost half their average body mass and smaller species are making up a larger proportion of European fish stocks as a result of global warming, a study published Monday has found.

"It's huge," said study author Martin Daufresne of the Cemagref Public Agricultural and Environmental Research Institute in Lyon, France.

"Size is a fundamental characteristic that is linked to a number of biological functions, such as fecundity - the capacity to reproduce."

Smaller fish tend to produce fewer eggs. They also provide less sustenance for predators - including humans - which could have significant implications for the food chain and ecosystem.

A similar shrinking effect was recently documented in Scottish sheep and Daufresne said it is possible that global warming could have "a significant impact on organisms in general."

Earlier research has already established that fish have shifted their geographic ranges and their migratory and breeding patters in response to rising water temperatures. It has also been established that warmer regions tend to be inhabited by smaller fish.

Daufresne and his colleagues examined long-term surveys of fish populations in rivers, streams and the Baltic and North Seas and also performed experiments on bacteria and plankton.

They found the individual species lost an average of 50 percent of their body mass over the past 20 to 30 years while the average size of the overall fishing stock had shrunk by 60 percent.

This was a result of a decrease in the average size-at-age and an increase in the proportion of juveniles and small-sized species, Daufresne said.

"It was an effect that we observed in a number of organisms and in a number of very different environments - on fish, on plankton, on bacteria, in fresh water, in salt water - and we observed a global shrinking of size for all the organisms in all the environments," Daufresne said in a telephone interview.

While commercial and recreational fishing did impact some of the fisheries studied, it "cannot be considered as the unique trigger" for the changes in size, the study published in the Proceedings of the National Academy of Sciences found.

"Although not negating the role of other factors, our study provides strong evidence that temperature actually plays a major role in driving changes in the size structure of populations and communities," the study concluded.