Co-author and UW biology professor Heidi Swanson sits next to charts generated by the nicheROVER tool. (Courtesy of Martin Schwalbe)
For the past couple of decades, scientists have used ratios of stable isotopes in tissue samples to determine an organism’s position, or niche in ecosystem. Until recently, however, scientists have been constrained by two-dimensional analyses of common isotopes such as carbon and nitrogen.
Biological researchers from Canada’s University of Waterloo teamed up with a statistician to create a tool that can analyze multiple ecological parameters and more precisely determine the overlap in species’ niches. The tool shows particular promise in identifying the impact of invasive species on an ecosystem.
“One of the first things you’ll notice with invasive species is they have an impact on the food webs of the ecosystems they invade,” said Michael Power, a biology professor at UW who helped design the tool. “The invasive species is essentially taking lunch from somebody else.”
Because the ratios of stable isotopes in an organism are derived from all the trophic pathways leading into it, they make great indicators of the relationships between coexisting individuals in a food web — including whose lunch is being stolen by whom. But examining those relationships in two dimensions can be misleading, Power said. Two species that share a common food source may not necessarily be in direct competition if, for instance, they feed in different depths or at different temperatures.
Power and his co-author, fellow biology professor Heidi Swanson, wanted a standardized means of exploring those relationships, but none of the common statistical techniques the researchers had employed prior could address them. Power admitted that an education in ecology doesn’t necessarily provide one with the resources to tackle complicated statistical analysis.
“We happily linked up with a statistician,” Power said. “We explained the problem to him, and he said, ‘Ah, I think I have some ways we can approach this.’”
The new tool, called nicheROVER, was first outlined in a paper featured in the journal Ecology. Not limited to isotope analysis, nicheROVER can compare species in any number of dimensions using parameters such as temperature, salinity and depth. The researchers have used it to study the impact of an invasive shrimp species in the Great Lakes and how it competes with other species for space and food. The tool shows potential for research into other invasive aquatic species as well, such as Asian carp and zebra mussels.
Although nicheROVER was developed over a couple of years, Power said it’s been a subject of consideration for quite a bit longer. When asked if the team faced any challenges in developing the tool, Power couldn’t help but poke fun at himself and his ecologist peers.
“Yeah — understanding what the statistician was saying sometimes,” he said, laughing. “We had to reign him in occasionally.”
NicheROVER is the basis of what Power calls a “common toolbox” for researchers, managers, and anyone else who can find a use for the tool. Although it was developed with ecologists in mind, Power says “it’s limited by the imagination of people and the problems that people have.”
“It was designed specifically to be flexible,” he said. “If we’ve achieved that, then it’s probably pretty hard to predict exactly how people will use it.”
Top image: Co-author and UW biology professor Heidi Swanson sits next to charts generated by the nicheROVER tool. (Courtesy of Martin Schwalbe)