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.

No abstract

Key words: marine and freshwater zooplankton, spatial heterogeneity, scaling, multiple abiotic and biotic generative processes . AbstractZooplankton spatial heterogeneity has profound effects on understanding and modelling of zooplankton population dynamics and interactions with other planktonic compartments, and consequently, on the structure and function of planktonic ecosystems . On the one hand, zooplankton heterogeneity at spatial and temporal scales of ecological interest is an important focus of aquatic ecology research because of its implications in models of productivity, herbivory, nutrient cycling and trophic interactions in planktonic ecosystems . On the other hand, estimating zooplankton spatial variation at the scale of an ecosystem, is a powerful tool to achieve accurate sampling design . This review concentrates on the spatial heterogeneity of marine and freshwater zooplankton with respect to scale . First to be examined are the concept of spatial heterogeneity, the sampling and statistical methods used to estimate zooplankton heterogeneity, and the scales at which marine and freshwater zooplankton heterogeneity occurs . Then, the most important abiotic and biotic processes driving zooplankton heterogeneity over a range of spatial scales are presented and illustrated by studies conducted over large and fine scales in both oceans and lakes . Coupling between abiotic and biotic processes is finally discussed in the context of the `multiple driving forces hypothesis' .Studies of zooplankton spatial heterogeneity refer both to the quantification of the degree of heterogeneity (`measured heterogeneity') and to the estimation of the heterogeneity resulting from the interactions between the organisms and their environment ('functional heterogeneity') (Kolasa & Rollo, 1991) . To resolve the problem of measuring zooplankton patchiness on a wide range of spatial scales, advanced technologies (acoustic devices, the Optical Plankton Counter (OPC), and video systems) have been developed and tested in marine and freshwater ecosystems . A comparison of their potential applications and limitations is presented . Furthermore, many statistical tools have been developed to estimate the degree of `measured heterogeneity' ; the three types most commonly used are indices of spatial aggregation, variance : mean ratio, and spatial analysis methods . The variance partitioning method proposed by Borcard et al. (1992) is presented as a promising tool to assess zooplankton `functional heterogeneity' .Nested patchiness is a common feature of zooplankton communities and spatial heterogeneity occurs on a hierarchical continuum of scales in both marine and freshwater environments . Zooplankton patchiness is the product of many physical processes interacting with many biological processes . In marine systems, patterns of zooplankton patchiness at mega-to macro-scales are mostly linked to large advective vectorial processes whereas at coarse-, fine-and micro-scales, physical turbulence and migratory, reproductive and swarm behavio...

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. Assemblages of coexisting species are formed by immigration from a regional pool of colonists and local interactions among species and with the physical environment. Theory suggests that the shape of the relationship between regional and local species richness may indicate the relative roles of dispersal and local interactions in limiting local diversity. Here we examine patterns of regional and local species richness in freshwater crustacean zooplankton to test whether linear (suggesting dispersal limitation) or curvilinear (suggesting saturation, via strong local control) functions best fit the data. Local richness appeared saturated when regions of different spatial extents were included on the same graph. However, this pattern was influenced by differences in scale among surveys. We corrected for the effects of regional scale by plotting mean local richness against the residuals of the species-landscape area relations. Controlling for the extent of the regional scale produced much more linear patterns, suggesting strong dispersal limitation. We present a simple graphical model to explain how variation among surveys in the geographic size of regions can produce apparent saturation of local diversity even if the underlying pattern of local and regional richness is linear. We also compare the predictive power of residual regional richness on local richness with that of several local features in a multiple regression model. Local richness exhibits strong relationships with both residual regional richness and pH.We argue that the relative strengths of local and regional processes depend on the definition of the regional scale. A variety of evidence suggests that local processes play a major role in generating differences in zooplankton diversity among lakes within a biogeographic region. Evidence for the importance of dispersal limitation comes largely from comparisons of lakes across very large scales. Our analysis suggests that linear patterns of local and regional diversity are not incompatible with strong local interactions.