Disease outbreaks: regime shifts & contagion

disturbanceJuan Carlos Rocha & Garry Peterson

Regime Shifts Regime shifts are abrupt reorganization of a system’s structure and function. A regime correspond to characteristic behavior of the system maintained by mutually reinforcing processes or feedbacks. The shift occurs when the strength of such feedbacks change, usually driven by cumulative change in slow variables, external disturbances or shocks.

external forcing reverses, the response variable will flip back to the original equilibrium, but at a differentlevel. Human activities can move the system along both of the horizontal axes. For example, fishing can actas external forcing by reducing the population rate of increase and also alter the internal trophic structure.

4. Modeling regime shifts

We concentrate here on general classes of model that can exhibit multiple equilibria for certain com-binations of parameter values. It is important to note that the three different types of regime shifts (smooth,abrupt, and discontinuous) can be generated from the same general models with different parameters. Thus,the three types are, apparently, special cases of the same general models, corresponding to different regionsof parameter space. There are large tracts of parameter space for which only a single equilibrium exists,corresponding to smooth or more abrupt regime shifts. This hierarchical modeling framework permitsstatistical tests of which type of regime shift fits the data best.

Our treatment summarizes the main features of these models that could be mechanisms for regime shifts,starting with models of single populations and progressing to coupled models of two or more species. Oneproblem with using models to describe the mechanisms that can lead to regime shifts is that, according tothe definition of regime shift that we have adopted here, several species or trophic levels should exhibit theshift. However, the simplest models describe only one population variable; two or three variables or trophiclevels rapidly develop very complicated responses. Thus, the models described here must be considered as‘‘samples’’ from a community responding as a regime. An alternative approach would be to start withecosystem models and to study the system dynamics. Models with many species are known to exhibitcomplex dynamics, thereby increasing the likelihood of discontinuous regime shifts.

Fig. 3. Catastrophe manifold illustrating that the three types of regime shifts are special cases along a continuum of internal ecosystemstructure. Adapted from Jones and Walters (1976).

J.S. Collie et al. / Progress in Oceanography 60 (2004) 281–302 287

(Collie 2004)

Regime Shifts Driven by diseases

Regime Shifts Impacting ‘Pest & disease regulation’

But disease outbreaks can be part of the process = feedbacks!• Classic example: Poverty traps on

coupled SES

• Cases where the shift occurs on the frequency of the disturbance lead to chaotic dynamics: strange cycles

• The frequency of disturbance (outbreaks - fire) is partially determined by the system’s history = memory

• Basin boundary coalitions: pesticides that kill natural enemies or development of drug resistance Ngonghala et al 2014

Scale, connectivity & speed

Next Steps: Embracing the complexity of diseases outbreaks

• Vulnerability depends on temporal and spatial connectivity

• Speed, connectivity and scale is increasing: what does it mean for resilience?

• Frontiers of research: theory development and evidence from case studies

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Thank you!

Questions?? e-mail: juan.rocha@su.se twitter: @juanrocha

slides: http://criticaltransitions.wordpress.com/ | data: www.regimeshifts.rog