AN EMPIRICAL-ANALYSIS OF COMMUNITY STRUCTURE REGULATION IN PERIPHYTON

Regulation of community structure was studied in an oligotrophic lake through experiments involving convergence of attached microalgal communities with initially differing structures. Convergence of a control and two experimental communities indicated that community structure was regulated, apparently toward a single. highly dynamic equilibrium. The rate of convergence was similar in the two experiments. and thus was independent of initial community structure. This rate was commensurate with average cell division rates measured independently. The estimated "characteristic response time", an aggregated community parameter, was 11 wk, indicating that the community could track yearly cyclical environmental variation, albeit with a lag. Environmental changes occurring over periods shorter than 11 wk, such as those observed in spring and autumn, may have left the community far from equilibrium for extended periods of time. By slowing cell division rates, phosphorus scarcity may have been the main factor underlying the sluggishness of community-level responses. The experimental protocol described here provides a means of quantifying community recovery and of estimating the rate of adjustment to equilibrium for periphyton communities.