Total Environment Research Themes 3–4 (2022) 100011
Contents lists available at ScienceDirect
Total Environment Research Themes journal homepage: www.elsevier.com/locate/totert
Ecological dynamics, resilience and sustainability William Grace Australian Urban Design Research Centre, 1002 Hay Street, Perth, Western Australia 6000, Australia
A R T I C L E Keywords: Model Equilibrium Ecosystem Collapse Predator Prey Resilience Sustainability
I N F O
A B S T R A C T This article describes a simple generic system dynamics model of resource dependency in ecosystems to explore the potential range of behaviours that can arise purely due to system structure. The model produces a small number of behaviours that replicate the observed real‐world behaviour of ecosystems but does not produce the less plausible outcomes produced in simpler predator–prey models (e.g. Lotka Volterra) such as exponential growth or exploding oscillations. The more limited range of behaviours is attributed to the inclusion in the model of species dependence on abiotic resource flows. The simulations explore the response of systems in equilibrium to various types of ‘shock’ and the outcomes are used to reflect on the concepts of resilience and sustainability. The results challenge the normative understanding of these terms and their relationship to each other. The results also reinforce the notion that shocks to the abiotic system flows at the foundation of all ecosystems present the greatest threat to ‘resilience’ as they affect all trophic levels.
1. Introduction The concepts of sustainability and resilience share a common focus ‐ they both involve study of the dependency of agents on resources of one type or another within a system, including in two of the well‐ known systems archetypes: limits to growth and tragedy of the commons (Braun, 2002). Resource constraints are the reason ‘nothing grows forever’. All animals, including humans, are dependent on a wide range of biotic and abiotic resources. Predators depend on prey, plants require air, water, minerals, and sunlight to grow. The term ‘sustainability’ has in some cases been used interchangeably with ‘resilience’, a term credited to C.S. Holling from his seminal article Resilience and Stability of Ecological Systems (C. S. Holling, 1973). Although Holling’s early work was associated with understanding the persistence of species in nature, the term ‘resilience’ has been expanded by him and others since to include concepts such as ‘trans formability’ and ‘adaptability’ in socio‐ecological systems (C. Holling, Walker, Carpenter, & Kinzig, 2004; Carl et al., 2010). Several articles have sought to draw connections between the terms ‘sustainability’ and ‘resilience’ (Berkes & Folke, 1998; Fiksel, 2006; Ludwig, Walker, & Holling, 1997; Redman, 2014), but none offer a satisfactory explanation of the meaning of each term or their relationship to each other in terms of system behaviour. The lack of clarity about what is meant by these terms has led to them being described as ‘boundary objects’, defined by some authors as ‘a theoretical perspective explaining the role of objects in inter and transdisciplinary research’ (Lundgren, 2020). While it is accepted that there
may be value in informing research, the vagueness of the terms is unhelpful in promoting a general understanding of what is sustainable and / or resilient and what is not. In order to answer this question, it is necessary to have a model that reflects the observed dynamic behaviour of ecosystems in nature. The biological resource dependency literature most often cited relates to the interactions between predators and prey. A Google Scholar search for ‘Predator prey models’ returns 900,000 results. Most of these are mathematical treatments of the species interactions using differential equations, the genesis of which is the widely cited Lotka‐ Volterra equations which are based on work originally published in 1910 (Lotka, 1910). Swart (1990) reports on the insight gained from using system dynamics modelling to explore system behaviour arising from the Lotka Volterra equations. Swart’s model is configured as shown in Fig. 1. Models of this type produce a range of behaviours. Terminology varies, but in this article the various terms have the following meaning. Equilibrium Oscillation Periodic
https://doi.org/10.1016/j.totert.2022.100011 Received 20 May 2022; Revised 30 August 2022; Accepted 30 August 2022 2772-8099/© 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
a condition in which stock (e.g. population) levels are constant over time. periodic variation in stock levels which may or may not vary in amplitude and / or frequency. a form of oscillation in which the amplitude and (continued on next page)