Journal Article

Species fluctuations sustained by a cyclic succession at the edge of chaos

Ballantine, Bill, Ellner, Stephen P., Huisman, Jef, Benincà, Elisa

2015

Overview

Although mathematical models and laboratory experiments have shown that species interactions can generate chaos, field evidence of chaos in natural ecosystems is rare. We report on a pristine rocky intertidal community located in one of the world’s oldest marine reserves that has displayed a complex cyclic succession for more than 20 y. Bare rock was colonized by barnacles and crustose algae, they were overgrown by mussels, and the subsequent detachment of the mussels returned bare rock again. These processes generated irregular species fluctuations, such that the species coexisted over many generations without ever approaching a stable equilibrium state. Analysis of the species fluctuations revealed a dominant periodicity of about 2 y, a global Lyapunov exponent statistically indistinguishable from zero, and local Lyapunov exponents that alternated systematically between negative and positive values. This pattern indicates that the community moved back and forth between stabilizing and chaotic dynamics during the cyclic succession. The results are supported by a patch-occupancy model predicting similar patterns when the species interactions were exposed to seasonal variation. Our findings show that natural ecosystems can sustain continued changes in species abundances and that seasonal forcing may push these nonequilibrium dynamics to the edge of chaos. Significance The intuitive and popular idea of a balance of nature has been criticized, because species interactions may generate nonequilibrium dynamics, such as oscillations and chaos. However, field evidence of chaos in ecosystems is rare. We report on a coastal community that has displayed striking fluctuations in the abundances of barnacles, mussels, and algae for more than 20 y. Data analysis reveals that these fluctuations reflect a cyclic succession alternating between stabilizing and chaotic dynamics during the species replacement. These results are supported by a simple patch-occupancy model, which predicts very similar dynamics when exposed to seasonal variation. Our findings provide a field demonstration of nonequilibrium coexistence of competing species through a cyclic succession at the edge of chaos.

• Publisher: National Academy of Sciences
• Subject: Algae / Animals / Biological Sciences / Biological variation / Bivalvia - physiology / Chaos / Cirripedia / Coexistence / Cyclic succession / Ecology / Ecosystem / ecosystems / Fluctuations / Mathematical models / Models, Biological / Mollusks / mussels / New Zealand / Nonlinear Dynamics / Phaeophyceae - physiology / Population Dynamics - statistics & numerical data / Rock-paper-scissors dynamics / Rocks / Rocky intertidal community / seasonal variation / Seasonal variations / Seasons / Species Specificity / Thoracica - physiology / Time Factors