Warming Affects Ecosystems Not Just Biodiversity

Ecosystems perform important tasks – like nutrient cycling, breakdown of waste and carbon storage – on which humans depend, so it's important we understand how climate change might affect them.

Researchers measured the effect of a 4-degree rise in temperature on communities of benthic organisms in fresh-water bodies – creatures that live at the 'bottom' of the ecosystem.

They found that the number of species in the community didn't change, but the balance of small and large organisms shifted significantly, and this in turn affected how efficiently organic material broke down in the water.
Lots of studies have looked into the potential ecological effects of global warming, but the relationship between community structure and ecosystem functioning in the context of climate change is not so well understood.
A team of researchers, led by Dr. Gabriel Yvon-Durocher of Queen Mary, University of London, wanted to see how warming might affect the structure of benthic communities and what impact that would have on ecosystem functioning. They established such communities in a series of outdoor tanks – designed to mimic shallow lakes – then raised the temperature of half the tanks by four degrees.

After allowing the communities a year to develop, PhD student Matteo Dossena sampled the experiment, once in April and again in October. He identified and weighed nearly 20,000 organisms ranging from micro-organisms through to invertebrates like dragonflies, whose larvae live in the sediments at the bottom of the water.

The study revealed that the diversity of species in the community was unaffected by warming, but the relative number of small versus large organisms was strongly affected by the temperature change.
The researchers also observed a large a seasonal difference in the effect of warming on community structure. In the spring, there was a big decline in the number of larger organisms, while in the autumn there were relatively more of the larger organisms in the warmed tanks. In the tanks that hadn't been warmed up, the size structure of the community stayed the same year-round.

"The effect of warming on the seasonality of community size structure was unexpected," says Yvon-Durocher. "From similar studies on plankton we were expecting to see an increase in smaller organisms at higher temperatures, but the marked seasonal change in response to warming was a surprise."

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