By studying organisms the naked eye can barely detect, two University researchers confirmed theories that diversity is important in biological communities.
Inspired by questions at a 1993 conference in Germany about whether biodiversity really matters from a biological standpoint, assistant professor of ecology Shahid Naeem and graduate student Shibin Li set out to prove that diversity has benefits. It is a theory that has been in place since the 1920s.
The $60,000 study was funded primarily by the McKnight Land-Grant Professorship and consisted of a series of micro-ecosystems in petri dishes where tiny organisms simulated real-life ecosystems.
The simulations were observed for 57 days. During this time, as many as 57 different generations reproduced. Because the organisms were very simple, smaller than the head of a pin, they could reproduce daily and, in some cases, within hours. Thus, the study could be conducted faster than if plants or animals were used, which can take months or years to produce a new generation.
Experimenting with varying numbers of organisms in each of the three different function groups, the researchers hoped to prove that having more organisms functioning at each level strengthens the reliability of an ecosystem.
The three main function groups found in an ecosystem, said Naeem, are autotrophes (or producers), decomposers and consumers. Autotrophes bring in the ecosystem’s nutrients. Decomposers break down dead matter. And consumers live off the products of the autotrophes or decomposers.
“Mathematically, an ecosystem will function with just autotrophes and decomposers,” Naeem said. This is because there always needs to be something bringing in nutrients and something to break them back down. “Autotrophes and decomposers are important. If either one were gone, the system would collapse.”
Naeem said that because only one species in each group is absolutely necessary for ecosystems to function, it suggests that anything else performing the same function is redundant, thus not necessary.
“Ecologists hate the word redundant,” Naeem said. “The idea is like it’s expendable.”
He likens redundancy in the environment to the mechanics in a car. “In a car, you have a foot brake and a hand brake. They both do the same thing, so in that sense they’re redundant. But you’d feel a lot safer if you had both — if you had a backup,” he said. “Engineers have known for a long time that redundancy is really important.”
The same is true in the environment. If that one species becomes extinct or migrates out, the system will be incredibly weakened, if not crumble entirely.
And what matters most is not how many species a system has, but how many species in each function group a system has.
“If you had a hundred different species that are all decomposers, but no plants, it’ll collapse,” Naeem said.
Having a diverse system with several redundant species helps to ensure the viability of a particular ecosystem. In the same regard, non-diverse ecosystems are prone to collapse.
“As you make systems more simple, you lose the ability to predict how they’re going to behave,” said Peter Morin, a professor of ecology, evolution and natural resources at Rutgers University in New Jersey, who has conducted similar studies. “When you lose species from an ecosystem, you do see deterioration. Losing species is a bad thing,” he said.
While Naeem said he believes most researchers will agree with the results, he has heard mild criticism that his micro-ecosystems do not have new species being introduced into them. In a normal biological system, species are joining an area all the time, Naeem said. In his study, organisms went extinct but were not reintroduced.
“That, per se, doesn’t invalidate the results,” said Dr. Steward Pickett from the Institute of Ecosystem Studies. He explained that, while “the approach is certainly interesting,” what Naeem and Li did is a very common way to set up an experiment.
“This is something that needed to be done,” Pickett said.