Vertical heterogeneity in zooplankton community structure: a variance partitioning approach

Abstract

The vertical structure of a freshwater zooplankton community was analysed quantitatively, in order to test the hypotheses that 1) vertical multivariate variability in community composition coincided with vertical variations in water temperature and that 2) the fundamental nature of the spatial structure in community composition would differ in mixed and stratified conditions. Multivariate methods were used to partition the variability in a spatio-temporal species dataset (12 sampling depths, 19 dates, 6 species) into pure spatial, temporal, environmental and shared components. Using this approach, 51 % of the variation of the zooplankton community could be explained. Broad-scale spatial organization in the zooplankton community (i.e. water column scale variation that could be explained as a simple first-order function of depth) accounted for 23 % of the explained variation. Approximately half of this variation was shared with depth-wise variations in water temperature variables. Due to the discontinuity of the thermally stratified water column, there existed a component of the shared variation between water temperature variables and zooplankton community structure that could not be explained by a simple first-order function of depth. By statistically modelling the discontinuous nature of the thermally stratified water column for a series of discrete time periods, thermocline position was found to explain between 9 and 22 % of the total variation in community structure. This indicated that spatial variations in the community composition included a discontinuous component, that coincided with the thermocline.