1. Regime Shifts and Leading Indicators
Michael Pace
University of Virginia

2. Outline Human accelerated environmental change Regime shifts
Theory of leading indicators
An experiment to test indicator theory
Microbial communities and regime shifts

4. Humans Global climate Loss of biodiversity change Land-use changes
Stratospheric ozone
depletion
Invasions of
Exotic Species
Toxification of
the Biosphere
Environmental change caused by multiple
and interacting human activities.
From Likens 1998

5. Regime Shifts
Massive reorganizations of ecosystems that occur abruptly and led to an alternate state
May be driven external causes or internal processes
Shifts may be difficult or impossible to reverse
Feedbacks that control ecosystem processes are different after a regime shifts
Example: switch during eutrophication from limitation by external nutrient loading to internal nutrient recycling

6. Regime Shift
Second Regime
Resilience
First Regime

7. Anderson et al. TREE in press

8. ENSO – Example of Regime Shift

10. El Nino Forecast

11. Shallow Lakes Shift from clear water, vegetation-dominated condition
To turbid, algal-dominated state
These shift are triggered by several switches

12. Algae + + grazers Turbidity Nutrients fish - - Vegetation waves
resuspended
sediments - -
Vegetation
waves

13. Zebra Mussels – Dreissena polymorpha

16. Zebra Mussel Dynamics 1991-2002

18. Hudson River Zebra Mussel Invasion

20. Effects on Hudson Ecosystem
Direct consumption – plankton
Change in light transmission - plants
Fouling – native bivalves
Competition – other filter feeders
Propagation through food web – fish
Creation of structure – benthic animals

21. Problem Regime shifts are difficult to predict
Ideally manage to avoid “going over the cliff”
Are there leading indicators that would warn of shifts prior to initiation?

22. Possible Leading Indicators of Regime Shifts From Theory
Increase in variance of time series
Variance shifts to lower frequencies (“red shift”)
Recovery rate from small perturbations increases (“critical slowing down”)
Known from physics, models of ocean thermohaline circulation,
economics, climate studies, and ecological models

24. Carpenter et al. 2008 Ecology Letters

28. Conclusions from Model
Signals of regime can be detected well in advance if the driver of the regime shift (e.g. fish harvest) changes more slowly than key ecological variables (e.g. phytoplankton production, zooplankton biomass)
However regime shifts can occur after the driver has already passed the critical point (i.e. ecosystem is already committed to going over the cliff when indicators go off)

29. Paul
Peter

30. Continuous Observation Methods
Daytime:
Nighttime:

33. Can Microbial Communities Drive Regime Shifts?
Perhaps rapid response and diversity of microbes results simply in community shifts to groups adapted to the new conditions
However competitive interactions, metabolic capacity, genetic composition or other phenomena might drive regime shifts that are determined by relative abilities with profound consequences for ecosystem structure and function

35. Initial Model Adapted modeling framework of Fellows et al.
Start with simple two group model of phytoplankton based on relative ability to compete for N and P (e.g. cyanobacteria vs. greens)

37. Status Elaborating model to build an approach to an experimental
Idea would be to fertilize a lake varying N:P ratio through time
Continuously monitor changes in phytoplankton (and others)
Measure leading indicators

38. The hypoxic zone of the Gulf of Mexico has approximately doubled
in size per unit nitrogen input. This partially reflects the accumulation
of organic carbon in sediments that supports increased oxygen demand
Turner et al EST

39. Perspective
Not all environmental change is abrupt (many transitions are gradual)
Not all regime shifts will have leading indicators
Continuous measurement systems provide opportunity to detect systems in transition (whether slow or fast)
How do we manage to avoid transitions
Defining indicators
Ability to detect “signals” of change
Proactive means to stay away from “the edge” and/or avoid “slow progressive” changes
What microbial capacities and processes will drive regime shifts particularly in relation to climate change?