Tag Archives: papers

Hysteresis and Heteroskedasticity (early view papers)

Only a handful of studies demonstrate the existence of hysteresis in bistable systems. In a follow-up from our earlier work, we study the recovery trajectory of a light-stressed plankton population in a chemostat experiment (early view in Oikos). We find that reverse trajectories can be explained by hysteresis, time-delays and adaptive process, all of which pose interesting questions for the behavior of bistable systems under changing conditions.

Recently, we summarized a set of measures that can be used as spatial indicators for detecting loss of resilience.  We  now add another measure that can be used as early warning of critical transitions in spatially explicit systems: spatial heteroskedasticity. In short, this indicator is the analog of conditional heteroskedasticity in timeseries (the non constant variance along a timeseries). We now expand its use from indicator of critical transitions in timeseries to spatial data (early view in Ecology & Evolution).

The use and misuse of resilience indicators as early warnings for regime shifts

Regime shifts have been a long sought theme of research in marine ecosystems. Controversies, new methods and alternative hypotheses on how to study and understand such marine regime shifts are summarized in the special issue of the Philosophical Transactions of the Royal Society on Marine regime shifts around the globe: theory, drivers and impacts that just appeared online. Thus, we couldn’t think of a better place to publish a review-research paper on the use and misuse of resilience indicators as early warnings for regime shifts in marine but not only systems.

Are Warning Signals specific to Catastrophic Transitions?

There is a lot of interest on the limits of resilience indicators and on whether they are uniquely associated with catastrophic transitions. We tried to shed light on that question in a short piece that just appeared in Oikos. There, we show that the same early warnings may signal non catastrophic transitions, but the same transitions are as well bifurcation points. Thus, it is not surprising that the same expectations for signals of deteriorating resilience are universal prior to any (local) bifurcation. The challenge remains in finding signals that would be specific to the catastrophic, unexpected, and irreversible shifts.

highlighted in Editor’s choice in Oikos

Flickering before a shift to eutrophication

Together with colleagues from China and the UK we just published work on a paleo limnological record in a big chinese lake that shows a transition to eutrophication during the last 30 years. Interestingly, the data offer the possibility to show that the system exhibits bimodality and that approaching to the permanent shift ‘flickering’ between the oligotrophic and eutrophic state may be observed. We compared these results to model simulations and we conclude that flickering may be more possible to detect in the most common ecological records at hand.

Review on anticipating critical transitions in last week´s issue in Science

Our review paper on Anticipating Critical Transitions summarizes the advancement and popularity in estimating early-warning signals for approaching transitions in a variety of disciplines together with some ground-breaking experimental demonstrations that followed the earlier review on early-warnings. In addition, new ideas are mapped out and the challenge of merging network perspectives on stability and collapse with early-warnign research is pioneered.

7 principles for enhancing the resilience of ecosystem services

Our long lasting project with the RAYS cohort just got appeared in a review/synthesis paper where we try to summarize basic principles that so far have been widely proposed to be fundamental for supporting the resilience of ecosystem services. Important part of this work is that we try to identify gaps in the existing research on resilience factors based on literature and expert opinion. This effort received quite some enthusiasm so that we decided to extent it into a book.

Model-based leading indicators for critical transitions

In a recent work with Tony Ives, we showed how modified linear models with time-varying parameters can be used to extract an indicator of instability for a time series that may be drifting towards a regime shift. The paper is available online in Ecosphere. The idea is simply that instead of fitting an autoregressive model and finding a fixed value for its parameters, to fit an autoregressive model with parameters that change based on the point one is along the time series. This is possible due to a Kalman filter fitting proceedure and seems to not require a too much long time series. We also show that fitting threshold autoregressive models can distinguish alternative attractors in a flickering time series. The code to execute all this is currently in Matlab, but we aim in converting it to an easy to use routine in the R environment.

Early Detection of Ecosystem Regime Shifts: A Multiple Method Evaluation for Management Application

The paper we were working on within the EUR-Oceans group for the Baltic Sea just appeared in PLoS One. We show for the first time how different methods for identifying regime shifts can be applied in the marine environment and how they can be interpreted. Hopefully this study will pave the way for same sort of applications in coastal and marine ecosystems.

Does predator interference cause alternative stable states in multispecies communities?

Our paper with Jiangfeng Feng and Egbert van Nes in Theoretical Population Biology just appeared online http://dx.doi.org/10.1016/j.tpb.2012.06.003 . We show that predator interference has a dual effect on the dynamics of multispecies predator prey communities: on one hand it increases their dynamical stability (in the sense of leading to stable equilibrium dynamics), while on the other hand it decreases their resilience (in the sense of increasing the number of alternative stable states that these communities may end to).