What Is Resilience? A Short Introduction

Abstract

Agent-based complex systems such as economies, ecosystems, or societies, consist of autonomous agents such as organisms, humans, companies, or institutions that pursue their own objectives and interact with each other and their environment (Grimm et al., 2005). Fundamental questions about such systems address their stability properties: How long will these systems exist? How much do their characteristic features vary over time? Are they sensitive to disturbances? If so, will they recover to their original state, and if so, why, from what set of states, and how fast? These questions are so important because the mere existence of agent-based complex systems is, in contrast to many systems studied in physics or chemistry, not granted but intriguing, calling for an explanation (Jax et al. (1998)). The building blocks of these systems – organisms or human actors – do not have a blueprint of the entire system in mind and behave accordingly, but follow their own objectives. Nevertheless, system-level properties emerge which allow the identification of the systems and their behaviours over time. Tropical forests, for example, can be self-similar over thousands of years and reliably provide functions and services that are important for us. Systems can, however, also collapse and lose their identity and functions. For example, a stock market can crash, or a savanna can turn into a scrubland due to overgrazing, rendering it useless as rangeland (Scheffer et al., 2009).