Regime shifts in ecosystems


Ecosystems are highly nonlinear systems that often admit multiple alternative stable states. Multiplicity of stable states in variable and disturbed environments is of high concern because of the possible occurrence of regime shifts, i.e. transitions to alternative stable states that involve loss of ecosystem function. One class of regime shifts are tipping-point phenomena, generally conceived as abrupt responses encompassing the whole ecosystem. Several ways of tipping have been studied, including a passage through a bifurcation point (B-tipping), a result of environmental fluctuations (N-tipping), or a result of fastly varying environmental conditions (R-tipping). Another class of regime shifts is gradual, domino-like processes. Such shifts are initiated by local disturbances that form spatially confined domains of an alternative state, which subsequently expand by front propagation. The purpose of this session is to present the state of art in regime-shift studies, highlighting mechanisms of regime shifts, possible early-warning signals for abrupt shifts, and means of reversing gradual shifts.