Succession in the aquatic Sarracenia purpurea community: deterministic or driven by contingency?

Abstract

The development of a community through time, or succession, is generally described as the orderly replacement of species until a deterministic, stable endpoint is reached. However, stochastic factors, coupled with intrinsic biotic factors, such as herbivory or predation, can cause communities within the same habitat to become highly dissimilar in composition. Much research on the succession of terrestrial systems has been conducted, but factors influencing the succession of a terrestrial system may not apply to aquatic systems. To determine whether succession in an aquatic system is deterministic or dominated by contingency of stochastic factors, and the role that higher trophic level interactions and resources have in shaping successional patterns, I followed community development and dynamics of the intermediate and bottom trophic level (protozoans and bacteria) in the model Sarracenia purpurea pitcher plant system throughout an entire growing season. By comparing these dynamics across pitcher plant leaves within the same bog, I was able to determine whether there is a predictable pattern for community assembly in this aquatic community. The results from this study suggest that rather than a sequential replacement of early colonizers with more competitive species through time, competitively superior species establish in newly formed communities simultaneously with less competitive species, which coexist throughout the growing season. Community assembly in this system can also be altered by stochastic events. Resources and predators had a variable effect on the patterns of community change observed during succession. Patterns of community assembly were also dependent on the trophic level examined but, for the bottom trophic level, not on the sampling method used.