Abrupt ecological changes, by definition, have a high magnitude and occur over short periods of time relative to typical rates of change for a given ecosystem. The potential for abrupt ecological change is growing due to pressures from global change, which is challenging societal and ecological adaptation. Abrupt ecological changes are difficult to diagnose because they can arise from multiple causes, such as rapid changes in external drivers, nonlinear responses to gradual changes in drivers, and interactions among multiple drivers and disturbances. We synthesize strategies for identifying causes of abrupt ecological change and highlight instances where abrupt changes are likely to occur. We also highlight areas where causality is uncertain.
Results/Conclusions:
We find at least seven realistic, general processes that can drive abrupt change in ecosystem states in response to changes in the mean of environmental drivers (e.g. nutrient addition, precipitation, or grazing rate). Abrupt changes can also be driven by changes in the variability of environmental drivers, resulting in at least fourteen more possible manifestations of abrupt ecological change. Interactions between multiple drivers further extend the possible processes responsible for abrupt ecological change. Empirical illustrations of these mechanisms include semi-arid landscapes, shallow lakes, temperate grasslands, agricultural production, animal populations, sub-alpine forests, and many more systems. Using theory and empirical examples, we present a framework that helps to identify the “bar of evidence” for identifying causes of abrupt change. Based on this framework, we recommend research strategies that emphasize reversals of directional changes in drivers, manipulating the variability of drivers and measuring the variability of system state, and factorial manipulations of drivers, including the mean and variability of drivers. Identifying abrupt changes is relatively easy, whereas diagnosing causes and anticipating future events are difficult. Yet, few ecological challenges are more important in our rapidly changing world.