Temporal variability of standing stocks of individual species, communities, and the entire plankton in two lakes of different trophic state : empirical evidence for hierarchy hheory and emergent properties?

Abstract

Hierarchy theory claims that the structure and function of ecosystems can be analyzed by defining different hierarchical levels which exhibit specific dynamic properties, e.g. higher levels vary on larger spatio-temporal scales than lower ones. These properties are attributed to complex asymmetric interactions between the different subunits and levels. In the present study, comprehensive data sets are evaluated in order to test this hypothesis empirically by analyzing the temporal variability of standing stocks at the levels of individual populations, communities, and the entire plankton in mesotrophic Lake Constance and oligotrophic Königssee. In both lakes, temporal fluctuations decrease consistently with increasing hierarchical levels of integration. The average coefficients of variation (CV) of standing stocks of algal, ciliate, rotifer, and crustacean species, respectively, are all higher than the CV of the total biomass of their communities. The entire plankton biomass, in turn, has a lower CV than each community. In oligotrophic Königssee, the overall level of variability at all hierarchical levels is smaller than in mesotrophic Lake Constance. In both lakes, rotifers exhibit the largest fluctuations on the species and community level. These results hold equally well for root-transformed time series. Thus, a striking regularity of decreasing temporal variability at higher levels of integration can be clearly identified using hard data despite the impact of various other factors influencing temporal fluctuations (e.g. trophic state, generation time, life history). The extent up to which variability changes between hierarchical levels depends on the lake and the considered time scale. This suggests that the smaller temporal fluctuations observed at superior levels of integration are not merely stochastic processes but provide empirical evidence for the validity of hierarchy theory and the related issue of emergent properties.