The influence of trophic status on the crustacean zooplankton community was investigated in lakes and reservoirs in temperate and subtropical-tropical regions. We tested if there is a consistent relationship between crustacean species richness, assemblages, and abundance and trophic indices such as total phosphorus and chlorophyll a. We also examined if these patterns differ between regions. Cumulative species richness and assemblages varied among regions. The greatest number of crustacean species was found in the temperate oligotrophic region with the largest number of lakes sampled. However, cumulative species richness was similar in temperate and subtropical–tropical regions when comparing subsets with a similar number of lakes and reservoirs. The relationships between species richness and latitude or trophic status were difficult to assess owing to imbalance among regions in number of lakes and reservoirs sampled and to biogeography and fish predation potential influences. Trophic status was associated with changes in abundance of all major crustacean zooplankton groups. Eutrophic ecosystems supported greater crustacean abundances at all latitudes. However, cladocerans and cyclopoids were more abundant in eutrophic lakes and reservoirs, whereas calanoids were more abundant in temperate oligotrophic lakes. Total phosphorus was found to be a better predictor of the biomass of major crustacean groups than chlorophyll a in all regions.

Paradigms based upon physical and geochemical bottom-up processes or trophic cascade/top down theory have been developed to explain heterogeneity of freshwater zooplankton, but these paradigms taken alone seem unable to encompass the full range of zooplankton variability and have led to controversy. The goal of the study is to test the hypothesis that both abiotic and biotic environmental factors, and spatial structuring, explain simultaneously the large-scale spatial heterogeneity of freshwater zooplankton in Québec lakes. Partial Canonical Correspondence Analysis (Partial CCA) was used to partition the variance of zooplankton species abundances into independent components: a) non-spatial environmental factors (physics, chemistry, morphometry, phytoplankton and fish communities), b) spatial component of environmental influence, c) pure spatial factors (geographic coordinates), and d) undetermined. Our study shows that pure and spatially-structured abiotic and biotic environmental factors (a+b) explain 48% of the variation of zooplankton within Québec lakes. Our study supports the multiple driving forces hypothesis and shows that the control model of the zooplankton structure within Québec lakes includes both abiotic factors (mainly related to the water chemistry gradients) and biotic bottom-up (phytoplankton) and top-down (fish) factors. Across our large geographic scale, the abiotic factors, especially those related to water chemistry, are the main environmental processes explaining zooplankton community structure variability within Québec. Pure spatial factors (c) have small and nonsignificant contribution (8%) to zooplankton variation. The large amount of unexplained variation (d: 44%) suggests that other external factors, operating at local scales and not taken into account in this study, can exert influence on lake zooplankton structure.