Salinity appears to be the main factor shaping spatial COI diversity of Corbicula lineages within the Chinese Yangtze River Basin

info:eu-repo/semantics/publishe

Nutrient enrichment homogenizes taxonomic and functional diversity of benthic macroinvertebrate assemblages in shallow lakes

Eutrophication alters the trophic dynamics in lakes and may result in biotic homogenization. How nutrient enrichment drives patterns of taxonomic and functional (i.e., trait‐based) homogenization of macroinvertebrate assemblages at within‐lake (local) and among‐lake (regional) scales is, however, not well understood. Taxonomic and functional compositions of macroinvertebrate assemblages in 41 lakes of the middle and lower reaches of the Yangtze River and Huaihe River were analyzed at within‐lake and among‐lake scales. Our results indicated that there was a significant difference in macroinvertebrate assemblages among lakes under different trophic status, and that total phosphorus was the major environmental factor that regulated both taxonomic and functional beta diversity of macroinvertebrate assemblages. That the abundances of pollution‐tolerant species (e.g., Limnodrilus hoffmeisteri and Microchironomus tabarui) increased with trophic state contributed the most to among‐lake dissimilarity. Functional beta diversity was significantly positively correlated with taxonomic beta diversity, while functional beta diversity was on average lower than taxonomic beta diversity. A combination of univariate and multivariate techniques revealed that nutrient enrichment homogenized taxonomic and functional diversity of benthic macroinvertebrate assemblages in shallow lakes at within‐lake and among‐lake scales, and that there was an overall trend toward taxonomic homogenization that exceeded the trend of functional homogenization. Thus, taxonomic and functional compositions should be considered simultaneously to improve understanding of the response of aquatic communities to anthropogenic disturbance, as the loss and gain of species may be influenced by species‐specific features, and functional composition may exhibit a relatively high correspondence with changes in environmental conditions

Do the ecological drivers of lake littoral communities match and lead to congruence between organism groups?

Lake littoral environments are heterogeneous, and different organisms typically show specific responses to this environmental variation. We examined local environmental and spatial factors affecting lake littoral biodiversity and the structuring of assemblages of phytoplankton, zooplankton and macroinvertebrates within and among three basins of a large lake system. We explored congruence of species composition and species richness among the studied organism groups to evaluate their general indicator potential to represent spatial variation in other groups. We expected that effects of water chemistry on plankton assemblages were stronger than effects of habitat characteristics. In contrast, we anticipated stronger effects of habitat on macroinvertebrates due to their mainly benthic mode of life. We also expected that within-basin spatial effects would be strongest on macroinvertebrates and weakest on phytoplankton. We predicted weak congruence in assemblage composition and species richness among the organism groups. Phytoplankton assemblages were mainly structured by the shared effects of water chemistry and large-scale spatial factors. In contrast to our expectations, habitat effects were stronger than water chemistry effects on zooplankton assemblages. However, as expected, macroinvertebrate species composition and richness were mainly affected by habitat conditions. Among-group congruence was weak for assemblage composition and insignificant for richness. Albeit weak, congruence was strongest between phytoplankton and zooplankton assemblages, as we expected. In summary, our analyses do not support the idea of using a single organism group as a wholesale biodiversity indicator

Metacommunity ecology meets bioassessment : Assessing spatio-temporal variation in multiple facets of macroinvertebrate diversity in human-influenced large lakes

Highlights • We examined drivers of 6 biotic metrics in a metacommunity context in two large lakes. • The relative roles of spatial, human-induced and natural factors were quantified. • The roles of spatial variables are comparable with local environmental conditions. • The relative roles of different drivers varied substantially among seasons. • Spatial processes, natural conditions and temporal variation should be considered.Metacommunity theory emphasizes that local communities are jointly affected by environmental filtering and spatial processes. However, the roles of spatial processes are often given insufficient attention in bioassessment practices, which may bias the assessments of ecological status based on biotic metrics. Here, we quantified the relative importance and the seasonal stability of spatial processes, natural conditions and human-induced factors in structuring variation in different bioassessment metrics based on macroinvertebrate communities. Our study systems were two extensively sampled large and shallow lakes with strong nutrient gradients related to human disturbance. The roles of different drivers were examined for three kinds of indicators: general diversity, trait-based and taxonomic distinctness metrics, and their performance in characterizing human disturbance was evaluated. Overall, human-induced and spatial factors were all important in explaining variation in the three types of bioassessment metrics. Contrary to our expectations, however, we found that the importance of spatial processes on bioassessment metrics can be comparable to the effects of local environmental conditions at the within-lake scale. Furthermore, the results showed substantial seasonal variability in the relative roles of different drivers, which might be linked to life-cycle seasonality of macroinvertebrates. As expected, trait-based metrics generally were best associated with human-induced variables in both lakes, whereas general diversity and taxonomic distinctness metrics performed poorly. The low effectiveness of taxonomic distinctness metrics might due to low species richness associated with high nutrient levels. To conclude, our results suggest that bioassessment cannot exclusively rely on the idea of environmental filtering even if we focus on fine spatial scales. We hence strongly urge that spatial processes, natural drivers and temporal variability should be better considered in combination in the development and application of bioassessment approaches. In addition, taxonomic distinctness measures should be used with caution, especially for the ecosystems and organism groups typically characterized by low species richness

Impact of nutritional and environmental factors on plasma urea and amino acid concentrations in pigs

A series of experiments were conducted to study variables that may affect concentrations of the blood plasma urea nitrogen (PUN) and free amino acids (AA) in 60 kg pigs. Pigs fed twice daily had postprandial peak PUN at 5 h and peak AA at 2 h after feeding. Pigs with ad libitum access to feed exhibited an almost constant PUN and AA during the 24-h period. Thirteen plasma nonprotein AA varied less than 10 essential or 9 non-essential AA in response to sampling times and two feeding methods. Adding cation (Na) to a corn-soybean diet elevated plasma citrulline but did not affect growth performance, PUN and plasma pH. Also, the Na addition shifted the forms of N excreted in the urine by increasing urea and decreasing ammonia, but total N from urea, ammonia and allantoin was the same for both groups. Water intake at 1.5 times feed intake as compared with 3 times feed intake increased PUN but did not affect ADG, feeding efficiency or plasma urea-cycle AA concentrations. A 2[superscript]3 factorial experiment with sex, CP at 13 or 15% and K added at 0 or.4% of diets resulted in greater PUN for barrows than gilts, for the pigs fed 15% CP and for those fed added K. A 2 x 2 x 3 factorial experiment with sex, ME at 3.33 or 3.55 Mcal/kg and CP at 13, 15 or 17% of diets resulted in a tendency for PUN to be greater in barrows than gilts, and a linear increase in PUN but linear decrease in total nonessential AA with increasing CP levels. In the two factorial experiments, barrows and gilts had similar AA; the sex difference in PUN suggested that gilts were more efficient in use of dietary N than barrows. The data also support the idea that more plasma essential AA were used for weight gain with increasing CP levels at high energy than at low energy intake. The curvilinear decline of PUN with energy intakes indicates that as lean tissue growth approached a plateau, further increases in ME intake resulted in relative more fat than protein deposition. The nine AA that differed between breed combinations have active AA transport systems that are Na[superscript]+ dependent, suggesting a breed difference in availability of energy for AA transport. This research demonstrates that, to effectively use PUN and plasma AA as indicators of rates of N deposition, it is necessary to control certain environmental variables. (Abstract shortened by UMI.)</p

Effects of Land Use Characteristics, Physiochemical Variables, and River Connectivity on Fish Assemblages in a Lowland Basin

Human disturbances can have severe environmental impacts on freshwater ecosystems. The main aim of this study is to detect the influences of physiochemical variables, land-cover characteristics, and river connectivity on fish assemblages in the Lake Chaohu Basin, China. A cluster analysis of river connectivity variables identified four groups of sites characterized by significantly different connectivity gradients at a local scale. These four groups of sites showed increasing connectivity from the upper reaches to the lower reaches. At the same time, among the four groups, the values of environmental variables generally increased from the upper reaches with less human activities towards the lower reaches with more human activities. For instance, some main physiochemical variables (e.g., river width, water depth, nitrate, phosphate) significantly increased among the four groups. In contrast, fish taxa richness and diversity indices were not significantly different among the four connectivity groups. However, fish assemblages showed significant variations among the connectivity groups (p = 0.026). In addition, the study determined that upper riparian land uses (e.g., woodland and grassland), flow velocity, and elevation were environmental variables regulating the variance of fish communities. As for the connectivity variables, only river order and the number of branches along a path to the left of the main stem affected the variance of fish communities. Therefore, new practices aimed at maintaining and even increasing riparian canopy coverage and the flow velocity of rivers should be integrated into local conservation planning for freshwater ecosystems, especially in the upper reaches of the basin

Influences of habitat type and environmental variables on benthic macroinvertebrate communities in a large shallow subtropical lake (Lake Taihu, China)

We investigated benthic macroinvertebrate communities in three contrasting habitats of a large shallow lake from February to November 2009. The three habitats differed markedly in their environmental characteristics (e.g., trophic status, substrate type, wind exposure). A total of 36 species were collected from the three habitats. The calculated descriptors (abundance, biomass and Pielou evenness index) differed significantly among the habitats. Generally, Tubificidae, Bivalvia and Gastropoda dominated the benthic community in abundance and biomass, but they varied greatly in abundance among the habitats. Analysis of similarities (ANOSIM) and non-metric multidimensional scaling (NMDS) analyses revealed significantly different macroinvertebrate assemblages among the habitats. North Bays had the lowest biodiversity and were exclusively dominated by pollution-tolerant species (e.g., Limnodrilus hoffmeisteri and Rhyacodrilus sinicus). Communities in the open lake contained intermediate biodiversity and were characterized by five species belonging to several taxonomic groups (e.g., Corbicula fluminea, L. hoffmeisteri and Gammarus sp.). Macrophyte-dominated habitats (East Bays) presented the highest diversity and evenness and were mainly characterized by gastropods. A canonical correspondence analysis (CCA) demonstrated that habitat-specific differences in trophic status, pollution level, wind-induced disturbance and macrophyte distributions were highly correlated with macroinvertebrate community structure