Ecologists Create a More Precise Way to Measure Human Impacts

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 significantly more precise than current methods and has revealed a dramatically lower ecological “tipping point” at which species are threatened.

The new method of statistical analysis was detailed online Feb. 1 in 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 are increasingly relying 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. 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, said 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.

Baker said the precision of their new method is significantly greater than methods that have been widely used for the past 40 years.

For example, a decade-old analysis widely cited by environmental professionals and policymakers suggests that it takes up to 15 percent of impervious surface (meaning 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. Environmental Protection Agency) 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 said.

“Our method of measuring response to degradation is more precise because we track the response of every species separately, and look specifically for places where the abundance or occurrence of many species changes simultaneously at a particular level of disturbance,” Baker said. “This allows us to detect, with a high level of statistical certainty, when we are approaching a point at which species are threatened, and whether the response is consistent with a community threshold.”