Alternate stable states (ASS) theory is a dominant conceptual framework for understanding processes that support resilience of ecological communities in the face of multiple anthropogenic disturbances. For decades, coral reefs have been cited as a classic example of ASS, yet this position remains highly controversial, largely because convincing empirical evaluations have been elusive. Using a combination of empirical measurements of positive feedback processes and simulation modelling, we assessed ASS in coral reefs of the Eastern Tropical Pacific (ETP) by identifying the potential for multiple basins of attraction from a mechanistic perspective. Using bioassays of algal growth and consumption, we quantified two spatially localized positive feedback mechanisms on coral reefs: increasing herbivore activity associated with higher coral abundances and amelioration of nutrient limitation leading to higher algal growth in areas with higher algal abundance. Analysis of a model of benthic community dynamics incorporating these feedbacks showed they were central to producing hysteresis and bistability in the model, two hallmarks of ASS. Further, reefs simulated with conditions matching those measured at Isla Contadora, Panamá, displayed ASS dynamics while producing spatial patterns matching field observations. This provides model-derived support, based on empirically measured conditions of ETP reefs, for the presence of ASS. Synthesis. The combination of experimental bioassays to measure feedback strengths and simulation models to evaluate the influence of those feedbacks provides a novel, non-destructive approach to evaluating ASS dynamics that can be applied in threatened ecosystems where classic approaches are not viable.
Bibliographical noteFunding Information:
We thank B. Fodor, J. Shannon, S. Hogan, L. Toth, I. Enochs and V. Brandtneris for assistance in the field; P.W. Glynn for access to long-term data; J. Mate, E. Ochoa and the Smithsonian Tropical Research Institute for logistical support in Panama. Computational efforts were supported by the Institute for Digital Research and Education at UCLA. This work was supported by an NSF Graduate Research Fellowship and UCLA Graduate Division fellowships to RM and NSF grant OCE-0002317 to PF and P. Glynn. JL-S was supported by the De Logi Chair in Biological Sciences and NSF grant OCE-1335657. We also thank Mike Gil, Gareth Williams and an anonymous referee for helpful comments on the manuscript.
© 2016 The Authors. Journal of Ecology © 2016 British Ecological Society
- alternate stable states
- coral reef
- determinants of plant community diversity and structure
- positive feedbacks