Human rules may determine environmental 'tipping points'

“Tipping points,” qualitative changes in an ecosystem that often result in reduced ecosystem health and are often difficult and costly to reverse, are of increasing concern for environmental scientists. An article appearing in the Proceedings of the National Academy of Sciences (PNAS) on April 18 suggests that people, governments, and institutions that shape the way people interact may be just as important for determining environmental conditions as the environmental processes themselves.

Tipping points were previously assumed to be fixed values by scientists. Now, a research collaboration involving biologists and economists indicates that these tipping points are not fixed in human-impacted ecological systems. They depend, instead, on how humans respond to a changing environment, according to lead author Michigan State University economist Richard Horan, Arizona State University economist Eli Fenichel, Bethel College biologist Kevin Drury, and the University of Notre Dame ecologist David Lodge.

The authors point to the many instances of tipping points that have resulted in catastrophic changes in ecosystems, such as climate change, collapsed freshwater and marine fisheries and changes wrought by invasive species. For example, an invasive species of sea lamprey devastated the Great Lakes, shifting a productive lake trout and whitefish industry to a collapsed fishery. Now, more than $17 million is spent annually on lamprey control measures to support the lake’s fisheries.

In the research described in the PNAS, the scientists studied invasive rusty crayfish. As with the sea lamprey, the crayfish has transformed many Michigan and Wisconsin lakes. Once luxuriant underwater forests, waterways inhabited by sport fish and a variety of smaller animals they feed on have become clear-cut forests with depressed sport fish populations. An outcome that occurred despite the presence of many fish, such as the smallmouth bass, that readily consume crayfish.

“Our work explored whether a shift from one lake condition with excellent habitat and lots of fishes to another lake condition with barren lake bottom is the inevitable result of invasion by crayfish or whether it is just one possible outcome,” Lodge said. “We asked whether we humans need to passively accept undesirable outcomes or whether, instead, the institutions and rules by which we make decisions can change the landscape of possibilities.”

The institutional rules shape the relationship among managers, users and ecological systems. If the system is mapped using only ecological characteristics, then managers may not account for human responses to change, such as changing decisions about whether to and how much to fish as fishing quality changes.

The PNAS study’s results showed that tipping points in human-impacted ecosystems are affected by regulatory possibilities that influence rules, which influence human behavior.

“Knowing this gives us reason for optimism: If we give regulators sufficient flexibility in their policy choices affecting human behavior, then it may be possible and cost-effective to manage ecological systems so that only desirable ecological outcomes arise and tipping points are eliminated,” Horan said. 

“Our results also create concern: If natural resource managers’ policy choices are overly restricted, then it might be too difficult or costly to alter human behaviors in ways to avoid tipping points,” added Fenichel, an assistant professor in the School of Life Sciences in ASU’s College of Liberal Arts and Sciences.

In particular, the researchers stress that their results highlight the importance of giving strong institutional support to regulatory agencies that aim to enhance societal well-being.

“Without strong institutional support, tipping points might disappear but not in a good way," Fenichel said. "Suppose lake managers remove crayfish but do not properly alter the behaviors of anglers, who overharvest fish? In such a scenario, crayfish removal would likely be ineffective means to restore the lake system and a waste of management dollars – if anglers continue to pull the ecosystem toward an undesirable state. Why invest to protect the system from crayfish if we are unable or unwilling to protect the system from humans?”

“Providing flexibility to managers, we might more often experience ecological outcomes that most people prefer – such as lots of plants, animals and sport fishes,” Lodge said.