Ecologists from the University of Maryland, Baltimore County and Baylor University in Texas have developed a new method for measuring the impact of human-caused environmental degradation on biodiversity that is much more precise than those currently used and has revealed a dramatically lower ecological "tipping point" at which species are threatened.
The new method of statistical analysis appears online in the Feb. 1 issue of the British Ecological Society's new journal Methods in Ecology and Evolution and includes a free download of a program to apply the analysis, created by co-author, and UMBC geography and environmental systems professor, Matthew Baker.
Environmental scientists have increasingly begun to rely on statistical methods for determining thresholds, or "tipping points," beyond which ecological systems are damaged by changes to the environment. More recently, ecologists have asked whether biological communities show similar responses � the proverbial "canary-in-the-coal-mine" test.
"This particular method came about because my colleague and I were trying to evaluate whether biological communities show a "tipping point response to environmental disturbance and degredation, mostly caused by human development near streams. We were looking for measures to do that - response measures that would characterize that - but found that existing measures weren't very sensitive. They might show huge changes but didn't show subtle changes," Baker explains.
"Scientists aren't really convinced, even though ecosystems can be shown to show tipping points in terms of their physical and chemical characteristics, it's not entirely clear that biological communities show that same response," he continues.
Accurately measuring these tipping points is important for protecting threatened species and better understanding how ecosystems respond to major changes such as global warming, coal mine leaching, agricultural pollutants or water-runoff from highly developed areas, says Baker, who with Ryan King, a biology professor from Baylor University, used stream invertebrate samples collected from Maryland tributaries by the Maryland Department of Natural Resources and data from Florida's Everglades in their analyses.
"
According to Baker the precision of their new method is significantly greater than methods that have been widely used for the past 40 years.
" They took a tool that already existed in their toolbox and rather than developing an entireely new technique, people started to evaluate the existing measures we had. Depending on the measures used, you found some weak evidence or no evidence of a tipping point. They find evidence of degredation but it's more like a linear decline. They aren't really focused on species-specific responses. They focused on the aggregate or entire community response," he says.
For example, a decade-old analysis widely-cited by environmental professionals and policymakers suggests that it takes up to 10-15 percent of impervious surface -- that is surface that does not absorb water, including roads, roofs, or parking lots -- or about 20 to 30 percent developed land in a given area before local water-systems no longer sustain normal aquatic life. Baker and King's new method demonstrates that aquatic life actually shows significant loss of biodiversity with only 1 to 3 percent developed land in a watershed.
A common practice by state and federal environmental protection agencies (U.S. EPA) is to rate the health of streams by comparing overall biotic life with data from "reference" streams using indices that combine various measures to provide a general scoring of health. This approach does a good job distinguishing highly degraded and relatively pristine systems, but isn't as clear about what happens when conditions fall in between, Baker says.
"What we do instead -- and is more intuitive and makes more common sense -- is we analyze every species seperately and look for a signal in the species responses. Then to understand what the community is doing we aggregate the signals of the species rather than using an aggregate measure to look for a signal," he says.
"It's not that the species are disappearing entirely, but that our actions are impacting the abundance of affected species. One-third of the biodiversity of a stream is impacted with just 2 to 3 percent of development. We used to think that development was benign, but now we see that it's not," Baker adds.
Source: Matthew Baker, UMBC
Writer: Walaika Haskins