Off the beaten track: How ecosystems fail to respond to environmental change

Abstract

Globally, ecosystems are exposed to human-induced changes in the environment. The effect of environmental changes on ecosystems can be understood with dynamical models. Such models have suggested that environmental change can trigger so-called critical transitions in ecosystems. A critical transition is a shift of a system to a qualitatively different dynamical regime. Critical transitions occur when conditions change beyond some critical threshold and include discontinuous, hard to reverse shifts to alternative stable regimes (catastrophic shifts), transitions from static to cyclic dynamics and the formation of spatially periodic patterns out of uniform states. Through equilibrium analysis the mechanisms behind these critical transitions can be studied in models by assuming that ecosystems are spatially uniform and in equilibrium. However, although frequently assumed, ecosystems often do not reside in a uniform equilibrium state. This dissertation investigates the response of ecological models that are "off the beaten track", i.e. that are not in a uniform equilibrium state, because of spatial patterning (Chapter 2), because of pulsed resource input (Chapter 3), because of cyclic dynamics (Chapter 4) or because of rapid environmental change (Chapter 5).