Social dynamics matter for ecosystem regime shifts: New modelling study in PNAS
Many ecosystem regime shifts, such as the 1980s Baltic cod collapse, have been collated and analysed with respect to their ecological dynamics. But what role do the people and societies with which these ecosystems are interconnected have in the dynamics of the collapse? Using the Baltic Sea cod fishery as a case study, we used mathematical modelling to show that social dynamics matter quite a lot! Read the paper here:
For social dynamics in the model of the cod fishery, we focused on fishers and their decisions regarding fleet size and time spent fishing, and whether Swedish west coast fishers moved into the Baltic. Influences on these decisions included price signals, government regulations and subsidies, fisher perceptions of the state of the fishery, and sunk cost effects (Fig 1). On the ecological side we included cod as well as three other species believed to play important roles in the cod collapse: herring, sprat and zooplankton. Our model showed, amongst other findings, that the stabilising effect of fisher decision-making may have prolonged the cod boom, but limits to their adaptability contributed to the cod stock’s eventual collapse. The broader implication is that social processes matter for ecological dynamics (such as regime shifts) and therefore cannot be ignored when modelling or managing natural resources or other ecosystems.
Figure 1: Components of our social-ecological model of the Baltic cod collapse. Reproduced from article cited above. Copyright PNAS 2015.
The paper is exciting because it develops one of the first and most detailed empirically-based mathematical models of a social-ecological system. It’s also methodologically innovative, applying a technique called generalized modeling to allow statements about the persistence and collapse of the social-ecological system (in this case the cod fishery) to be made without detailed knowledge about the precise forms of the causal links in the system. Authors on the paper were Steve, Kirill, and Maja from SES-LINK; our colleagues at the Stockholm Resilience Centre Susa, Jonas, Thorsten, Henrik and Wijnand who have extensive research expertise in the Baltic Sea; and fisheries economist Martin Quaas from Kiel.