Study Looks at How Rapid Change in Ecosystems Impacts Species Survival 

Columbia Basin Bulletin

February 1, 2008  

In a laboratory at Oregon State University , some giant water bugs are swimming happily in a small aquarium -- the sole survivors of a population that had survived for thousands of years in a mountain stream near Tucson , Ariz. , but during a severe 2004 drought went locally extinct.

These water bugs are similar, but not genetically identical, to many others in that region, and by themselves represent no ecological catastrophe. But conceptually, they are part of what ecologists fear may become far more common in the near future --– species or populations that struggle and sometimes disappear because they cannot keep pace with rapidly changing climate or ecosystem conditions.

A recently published study on this phenomenon outlines how many species have a surprising ability to adapt to, evolve with and even depend on very different climatic and ecological conditions -- cycles of fire, flood, drought or other events -- but sometimes simply cannot survive if the changes are too rapid or unpredictable.

"The more we study natural disturbance regimes, it becomes clear that species can adapt if the disturbances are consistent and take place over a long enough period of time," said David Lytle, an entomologist and OSU assistant professor of zoology. "But the key question is the pace and speed of evolutionary change, and whether the species can keep up. In many cases, we are now finding that they cannot."

The findings, Lytle said, are relevant to everything from water bugs in desert streams to salmon in the Pacific Northwest and thousands of species in between, both aquatic and terrestrial. The study was published in Proceedings of the Royal Society -- B.

In this research, scientists examined the behavior and survival of a giant water bug, Abedus herberti, in the Sky Islands mountain ranges of southern Arizona , where isolated populations of these flightless aquatic insects have lived for tens of thousands of years. The insects have evolved the ability to use rainfall as a cue and leave the streams during major flooding events, escaping destruction.

However, some of the separated populations lived in canyons where flash floods were often caused by distant storms, which provided no warning that a flash flood was coming. The research found that they would get periodically wiped out by these floods and have to slowly re-populate the area.

"Where the insects had any type of indicator that floods were imminent, such as heavy rain, they had evolved a behavior to deal with it," Lytle said. "But where the events were just too sudden and unpredictable, they periodically just got wiped out."

This is one of the first studies that has documented a species' ability to adapt to threatening circumstances, given adequate cues and enough evolutionary time, Lytle said. It also points out the vulnerability of species to unpredictable or rapidly changing events, even if they have been happening for thousands of years.

The implications, he said, may hit fairly close to home in Oregon if a warming climate causes more winter precipitation to fall as rain, instead of snow, as has been predicted.

"Many Oregon aquatic species have evolved over thousands or millions of years to expect certain types of events, such as summer droughts and spring floods due to snowmelt," Lytle said. "If these systems change fairly suddenly, it's reasonable to believe there will be some widespread ecological impacts. You would expect that some species will not be able to keep pace, and may become at least locally extinct."

The drought that destroyed the water bug population in Arizona 's French Joe Canyon , Lytle said, appeared to be as severe as anything in hundreds of years. It's not certain what the underlying cause of the dried-up streams were, he said, but climate change and declining groundwater levels due to human water use are reasonable suspects.

Salmon, Lytle said, are another species whose ecology -- spawning, emergence from larval stage, migration -- is closely tied to predictable water flow events. At least one factor in their decline could clearly be the increasingly unpredictable and changing nature of Pacific Northwest stream systems, he said. And many terrestrial species could be affected by such things as the changing fire regimes in Pacific Northwest forests, he said.

In earlier research, OSU studies have also found that the link between disturbance events and species survival is so tight that many species depend on these disturbances -- whether they are periodic floods, windstorms, or droughts -- as part of their basic ecology and survival. Changes in those disturbance events can open to the door to invasive species with different ecological requirements, the research showed.

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