Regime shifts: Can theory illuminate the mechanisms?
Jeremy Collie, Ph.D.
University of Rhode Island
Wednesday, May 4, 2005
Pacific Forum – 3:00 p.m.
Regime shifts mean different things to oceanographers and ecologists. Oceanographers define regime shifts as persistent changes in coupled ocean-atmosphere systems, while limnologists focus on the internal feedbacks that maintain regimes in freshwater ecosystems. Whereas the role of physical variability is paramount in marine ecosystems, most lakes are impacted by human activities, especially eutrophication. What do these apparently disparate points of view have in common? There is increasing evidence that ocean-scale climate variability affects terrestrial and lake ecosystems. Likewise, humans now influence ecosystems on a global scale. Marine biota appear to amplify oceanic variability, suggesting ecological feedback mechanisms. Many simple ecological models can display multiple equilibria, raising the possibility of their existence in real populations. A structured protocol has been published for identifying and characterizing regime shifts. We apply this protocol to putative examples of regime shifts in marine ecosystems, such as the Danish Limfjord, coral reefs, Georges Bank haddock, and the Benguela upwelling system. For each example, we examine the relative contribution of ocean forcing and human activities, as well as the evidence for multiple equilibria. This approach is intended as a step toward elucidating the mechanisms of regime shifts.