Horizontal and temporal patterns in crustacean zooplankton communities
were analyzed in two small, oligotrophic lakes which were morphologic
ally and chemically similar, but had contrasting fish communities. Ran
ger Lake was dominated by two bass species and the planktivores number
ed < 25 ind. ha-1. Mouse Lake had no large piscivores and planktivores
numbered > 1200 ind. ha-1. There were significant differences in the
distribution of zooplankton taxa and size classes between sampling sta
tions. In Ranger Lake, the smallest size classes were more abundant at
the deeper stations and the larger individuals were more abundant at
the shallower stations. In Mouse Lake, the smaller individuals were mo
re common at the shallow stations and the larger individuals were more
common at the deeper stations. These differences suggest medium scale
patterns induced by vectorial forces, but modified by species specifi
c migration patterns. We tested the hypothesis that horizontal heterog
eneity should be influenced by planktivore density and found that none
of the taxa showed significant between-lake differences in the varian
ce-mean regressions. We also tested the hypothesis that larger taxa sh
ould be more heterogeneous and we found that cladocerans were more het
erogeneous than copepods and nauplii. In terms of sampling methodology
our data suggest that the between-station variability was so high tha
t a single mid-lake sample would certainly lead to completely unaccept
able errors in the estimation of population densities and biomasses.