Forecasting the limits of resilience: integrating empirical research with theory

Abstract

Despite the increasing evidence of drastic and profound changes in many ecosystems, often referred to as regime shifts, we have little ability to understand the processes that provide insurance against such change (resilience). Modelling studies have suggested that increased variance may foreshadow a regime shift, but this requires long-term data and knowledge of the functional links between key processes. Field-based research and ground-truthing is an essential part of the heuristic that marries theoretical and empirical research, but experimental studies of resilience are lagging behind theory, management and policy requirements. Empirically, ecological resilience must be understood in terms of community dynamics and the potential for small shifts in environmental forcing to break the feedbacks that support resilience. Here, we integrate recent theory and empirical data to identify ways we might define and understand potential thresholds in the resilience of nature, and thus the potential for regime shifts, by focusing on the roles of strong and weak interactions, linkages in meta-communities, and positive feedbacks between these and environmental drivers. The challenge to theoretical and field ecologists is to make the shift from hindsight to a more predictive science that is able to assist in the implementation of ecosystem-based management.

Figure 1.

Experimental design with sites randomly allocated to strata across a ‘landscape’. This landscape could represent a stress or disturbance gradient or spatial structure in the density or size of key species or diversity within a functional group. This design and, more generally, the construction of gradients facilitate the use of co-variables to tease apart the effects of different factors on experimental processes and multi-scale analysis (Thrush et al. 1997; Thrush et al. 2000; Hewitt et al. 2007).

Figure 2.

Movement of pristine communities into a stressed state and the resilience of degraded communities. The effect of key species or members of a functional group on the positioning of a regime shift along a stress or disturbance gradient is dependent on whether the species are sensitive or resistant. Furthermore, whether a regime shift or a gradual change occurs depends on how positive feedbacks are affected by stress or disturbance and the connectivity among patches.