Wilder weather exerts a stronger influence on biodiversity than steadily changing conditions

Science Daily: An increase in the variability of local conditions could do more to harm biodiversity than slower shifts in climate, a new study has found. Climate scientists predict more frequent storms, droughts, floods and heat waves as the Earth warms. Although extreme weather would seem to challenge ecosystems, the effect of fluctuating conditions on biodiversity actually could go either way. Species able to tolerate only a narrow range of temperatures, for example, may be eliminated, but instability in the environment can also prevent dominant species from squeezing out competitors.

"Imagine species that have different optimal temperatures for growth. In a fluctuating world, neither can get the upper hand and the two coexist," said Jonathan Shurin, an ecologist at the University of California, San Diego who led the project. Ecologists have observed similar positive effects on populations of organisms as different as herbacious plants, desert rodents, and microscopic animals called zooplankton.

Now a study of zooplankton found in dozens of freshwater lakes over decades of time has revealed both effects. Shurin and colleagues found fewer species in lakes with the most variable water chemistry. But lakes with the greatest temperature variations harbored a greater variety of zooplankton, they report in the journal Ecology Letters January 21.

Their study considered data from nine separate long-term ecological studies that included a total of 53 lakes in North America and Europe. In addition to sampling zooplankton, scientists had also taken physical measurements repeatedly each season for periods ranging from 3 to 44 years.

From these data, they calculated the variability of 10 physical properties, including pH and the levels of nutrients such as organic carbon, phosphorous and nitrogen. Temperatures and the amount of oxygen dissolved in the water at both the surface and bottom of each lake were also included. The authors also teased apart variation based on the pace of change with year-to-year changes considered separately from changes that occurred from season-to-season or on more rapid timescales.

Zooplankton populations respond quickly to changes because they reproduces so fast. "In a summer, you're sampling dozens of generations," Shurin said. "For mammals or annual plants, you would have to watch for hundreds or thousands of years to see the same population turnover."…

The zooplankton beroidae (beroidae) are often found accompanying swarms of medusae in the water column (not freshwater like the zooplankton referred to in the article). Shot by Shane Anderson