Comparison of Temporal and Spatial Variation in the Zooplankton of a Lake by Means of Variance Components

Abstract

A standard 2—way analysis of variance is used to separate components of variance in zooplankton abundance data (individuals per unit area). The sampling design and interpretation, which are applied to Lake Lanao, Philippines, require that samples be (1) widely distributed over the limnetic zone, (2) representative of the full range of temporal variation, and (3) free of significant autocorrelation. Under these conditions the relative importance of spatial and temporal variation can be quantitatively compared for individual zooplankton species and developmental stages. The analysis yields variance components associated with (1) stations, (2) dates, (3), station—date interaction, and (4) error. The station component is interpreted as a quantitative measure of "fixed" spatial patchiness, which is caused by temporally stable differences between stations. The dates component is a quantitative measure of the variation in abundance through time, and the interaction component is a quantitative measure of "emphemeral" spatial patchiness. Ratios between these variance components provide a measure of their relative importance. The analysis shows that, among 16 zooplankton species and developmental stages, (1) there are radical differences between species in the relative importance of spatial and temporal variation, (2) the 2 spatial components of variance (fixed plus ephemeral) exceed the temporal component of variance for about half the species, (3) the ephemeral component of spatial variance is typically much greater than the fixed component of spatial variance,and (4) the spatial component of variance has a much greater relative importance in the large cladoceran species than in other zooplankton species. Interspecific differences in the relative importance of spatial and temporal patchiness may be related to differences between species in adaptive strategies for survival in the limnetic zone.