Pond scum: More Than Meets the Eye
Slimy substance examined in joint UU直播 and Oxford study on biodiversity
While pond scum may conjure up images of festering bacteria to most people, the slimy substance is actually providing a group of UU直播 and Oxford University researchers with clear answers into biodiversity.
In the August 3 issue of Nature, UU直播 Biology researchers Rees Kassen and Graham Bell describe how a team of scientists from both universities are using pond scum -- more precisely a bacterium called pseudomonas fluorescens -- to better understand species diversity patterns in nature. To conduct their research, the biologists have taken the bacteria out of the ponds and brought it into the glass vials of their laboratories. Studying bacteria in vials, the authors explain, "has allowed us to test fundamental theories of biodiversity directly, on a scale that is experimentally easier to trace."
Three-decade mystery unlocked
Using pond scum, the research team has been examining how species diversity tends to be highest in regions where the productivity -- or the rate at which energy becomes available to a population - is moderate. Simply put, species diversity shows a humped-shaped relationship with productivity.
Biologists have long known that different species can coexist if they are specialized in different niches within an environment. Yet when one niche produces many more individuals than another, diversity cannot be maintained because the individuals from the more productive niche overwhelm those from the less productive niches. Over the past three decades, some nine hypotheses have tried to explain this pattern. Since diversity/productivity patterns occur over very large spatial scales - about the size of an average U.S. state -- all previous pattern hypotheses remained theoretical -- until now.
First experiments produce striking results
Researchers at UU直播 and Oxford were the first to conduct experimental tests of the productivity-diversity pattern. The researchers mimicked a statewide productivity gradient by growing bacteria in vials containing different concentrations of nutrients. Within each vial, the environment could be variable or uniform, depending on whether the vial was left undisturbed on a shelf or shaken.
The humped-shaped pattern was observed along productivity gradients where the environment within the vials was variable. If the environment within the vial was uniform, the hump disappeared completely. This proved to the researchers that a variable environment was absolutely essential to get the humped-shaped relationship. The humped-shaped pattern arises, they suggest, because different regions, or niches, within a variable environment produce different numbers of individuals. This imbalance, the researchers explain, is characteristic of very low and very high productivity environments. Only at intermediate productivity are the population sizes balanced in a way that allows different species, each specialized to different niches, to coexist.
The UU直播 and Oxford teams will continue to examine pond scum to obtain more clues on biodiversity patterns. "This time," Kassen says, "we聮re examining how diversity patterns are disturbed when physical, environmental or predatorial factors come into play and how these can affect species in any given area."
