Total fish biomass per unit area was positively correlated with total phosphorus, total nitrogen, chlorophyll a, and inversely correlated with Secchi disk transparency in 65 Florida (U.S.A.) lakes selected to range from oligotrophic to hypereutrophic. Species numbers were positively related to lake surface area but not trophic state. There were some shifts in species composition with changes in trophic state, though only a few species showed significant changes in their standing crops. In particular the recreationally important centrarchids did not show important changes with trophic state, and there were no critical points on the trophic spectrum where there were dramatic changes in fish abundance or standing crops. The facts that Florida lakes do not have deep, cold hypolimnia, do not have salmonid species, and have no ice in the winter are among the possible reasons that the more eutrophic Florida lakes do not show the same changes in fish populations often described for northern lakes.Résumé : Il y avait une corrélation positive entre la biomasse totale de poissons par unité de surface et le phosphore total, l'azote total et la chlorophylle a, et une corrélation inverse entre cette biomasse et la transparence mesurée à l'aide du disque de Secchi, dans 65 lacs de Floride (É.-U.) allant d'oligotrophes à hypereutrophes. Les nombres d'espèces étaient liés positivement à la superficie des lacs, mais non à leur état trophique. La composition des espèces variait quelque peu avec l'état trophique, mais seules quelques espèces accusaient des différences importantes dans le nombre d'individus. Plus particulièrement, les centrarchidés importants sur le plan récréatif n'accusaient pas d'importants changements avec l'état trophique, et le spectre trophique ne présentait aucun point critique correspondant à des changements dramatiques de l'abondance ou du nombre d'individus. L'absence d'un hypolimnion froid et profond, l'absence de salmonidés et l'absence de glace en hiver comptent parmi les raisons pouvant expliquer pourquoi les lacs de Floride plus eutrophes n'accusent pas les mêmes variations de population de poissons dont on a souvent fait état dans les lacs nordiques.[Traduit par la Rédaction]

Aim\ud \ud We studied global variation in beta diversity patterns of lake macrophytes using regional data from across the world. Specifically, we examined (1) how beta diversity of aquatic macrophytes is partitioned between species turnover and nestedness within each study region, and (2) which environmental characteristics structure variation in these beta diversity components.\ud Location\ud \ud Global.\ud Methods\ud \ud We used presence–absence data for aquatic macrophytes from 21 regions distributed around the world. We calculated pairwise-site and multiple-site beta diversity among lakes within each region using Sørensen dissimilarity index and partitioned it into turnover and nestedness coefficients. Beta regression was used to correlate the diversity coefficients with regional environmental characteristics.\ud Results\ud \ud Aquatic macrophytes showed different levels of beta diversity within each of the 21 study regions, with species turnover typically accounting for the majority of beta diversity, especially in high-diversity regions. However, nestedness contributed 30–50% of total variation in macrophyte beta diversity in low-diversity regions. The most important environmental factor explaining the three beta diversity coefficients (total, species turnover and nestedness) was elevation range, followed by relative areal extent of freshwater, latitude and water alkalinity range.\ud Main conclusions\ud \ud Our findings show that global patterns in beta diversity of lake macrophytes are caused by species turnover rather than by nestedness. These patterns in beta diversity were driven by natural environmental heterogeneity, notably variability in elevation range (also related to temperature variation) among regions. In addition, a greater range in alkalinity within a region, likely amplified by human activities, was also correlated with increased macrophyte beta diversity. These findings suggest that efforts to conserve aquatic macrophyte diversity should primarily focus on regions with large numbers of lakes that exhibit broad environmental gradients

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Stent patients had significantly lower acute complications compared with surgery patients or BA patients, although they were more likely to require a planned reintervention. At short-term and intermediate follow-up, stent and surgical patients achieved superior hemodynamic and integrated aortic arch imaging outcomes compared with BA patients. Because of the nonrandomized nature of this study, these results should be interpreted with caution.

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School of Forestry, Fisheries and Wildlife, 112 Stephens Hal!, C7niversity of Missouri-Columbia, Columbia, MO 65211, LTSPl Houea, M. V., AND J. R. JONES. 1983. Factors affecting the relation between phosphorus and chlorophyll a in midwestern reservoirs. Can. J. Fish. Aquat. Sci. 40: 192-199.The mean chlorophyll a (mg/m" yield per unit of total phosphorus (mg/m3) (P-C relation) in 96 midwest reservoirs and the variance a b u t this yield was similar to relations for natural lakes reported in the literature. The remaining error term for this relation could not be reduced by adding variables for nitrogen, zooplankton abundance, or hydrologic flushing rate. In reservoirs with ratios of total nitrogen to total phosphorus of less than 10, nitrogen accounted for the same amount of variance in chlorophyll a as did phosphorus. Using partial regression path analysis, we found that when the concentration of phosph(.srus was held constant, increasing the concentration of inorganic suspended solids (rng/L) significantly decreased chlorophyll a. The following multivariate equation was developed to account for the effect of inorganic solids on the P-C relation:log chlorophyll a = -0.47 + 1.13 log total phosphorus -inorganic suspended solids ' ) '03 ( total phosphorus , This equation accounted for 7% more variance than the univariate equation and the 95% predictive confidence interval, at an average phosphorus concentration, was reduced by 10%. This equation should be useful for predicting chlorophyll a in lakes with inorganic turbidities. When Secchi transparency data were regressed on both chlorophyll u and inorganic suspended solids, they accounted for 42% more variance in transparency than did chlorophylI a.

Stable carbon ( 13 C) and nitrogen ( 15 N) isotopes were employed to elucidate energy flows and trophic interactions in Lake Apopka, a hypereutrophic lake in central Florida, U.S.A. Isotope compositions of lake biota ranged from 27·1 to 3·0‰ for 13 C, and from 3·7 to 13·9‰ for 15 N. The food web was based primarily on plankton production with diatoms, Microcystis and zooplankton dominating the diet of fish. Carbon isotope evidence showed that pico-and nano-phytoplankton were not a direct carbon source for fish, but were important to zooplankton. 15 N mass balance estimates indicated that planktivorous fish obtained 48-85% of their diets from zooplankton. The 3‰ range of 15 N in gizzard shad reflected increasing dependence on zooplankton as fish grew whereas the positive relationship between total length and 15 N of largemouth bass reflected increasing predation on larger planktivorous fish with growth. The broad ranges of 13 C ( 25·9 to 9·5‰) and 15 N (5·8 to 14·4‰) of blue tilapia were indicators of diet diversity. Two presumed omnivores (brown bullhead and white catfish) and piscivores (black crappie, largemouth bass and Florida gar) were found to depend on planktivorous fish. However, stable isotope data revealed no trophic links between blue tilapia, an abundant fish in the near-shore area, and piscivores.

We studied community–environment relationships of lake macrophytes at two metacommunity scales using data from 16 regions across the world. More specifically, we examined (a) whether the lake macrophyte communities respond similar to key local environmental factors, major climate variables and lake spatial locations in each of the regions (i.e., within-region approach) and (b) how well can explained variability in the community–environment relationships across multiple lake macrophyte metacommunities be accounted for by elevation range, spatial extent, latitude, longitude, and age of the oldest lake within each metacommunity (i.e., across-region approach). In the within-region approach, we employed partial redundancy analyses together with variation partitioning to investigate the relative importance of local variables, climate variables, and spatial location on lake macrophytes among the study regions. In the across-region approach, we used adjusted R2 values of the variation partitioning to model the community–environment relationships across multiple metacommunities using linear regression and commonality analysis. We found that niche filtering related to local lake-level environmental conditions was the dominant force structuring macrophytes within metacommunities. However, our results also revealed that elevation range associated with climate (increasing temperature amplitude affecting macrophytes) and spatial location (likely due to dispersal limitation) was important for macrophytes based on the findings of the across-metacommunities analysis. These findings suggest that different determinants influence macrophyte metacommunities within different regions, thus showing context dependency. Moreover, our study emphasized that the use of a single metacommunity scale gives incomplete information on the environmental features explaining variation in macrophyte communities.Electronic supplementary materialThe online version of this article (10.1007/s00442-018-4294-0) contains supplementary material, which is available to authorized users.