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Quadratic Regressions (quadratic + regression)
Selected AbstractsHerbage growth rates on heterogeneous swards as influenced by sward-height classesGRASS & FORAGE SCIENCE, Issue 1 2009ahin Demirba Abstract The contribution of four classes of sward height to daily herbage growth rates of a heterogeneous sward in eight periods throughout a grazing season was investigated in two continuous cattle-grazing systems differing in intensity (moderate stocking rate: MC; lenient stocking rate: LC). At the beginning and end of periods of 12 to 28 d, the compressed sward height (CSH) was measured in exclusion cages at eighteen fixed points per cage to derive daily growth rates for the four classes of sward height. Stratified calibrations were made to relate sward height to herbage mass for each treatment in each period. Quadratic regressions described the relationship between herbage growth rate and initial CSH for each treatment in each period. For scaling up to the scale of the plot, CSH was measured monthly at 100 points per plot. Daily herbage growth rates declined from more than 100 kg dry matter (DM) ha,1 d,1 on both treatments at the beginning of the grazing season to 20 kg DM ha,1 d,1 or less, especially on treatment LC. This was due to the larger area covered by tall herbage on treatment LC than on treatment MC. On treatment MC, daily herbage growth rate was predominantly derived from short sward areas of up to 12 cm in height while sward areas taller than 12 cm contributed most to daily growth rates on treatment LC in early summer. The method used is considered suitable for estimating daily herbage growth rates of different classes of sward height in extensively managed pastures and can easily be adapted to deal with more heterogeneous swards than used in this study. [source] The evolutionary species pool hypothesis and patterns of freshwater diatom diversity along a pH gradientJOURNAL OF BIOGEOGRAPHY, Issue 3 2005Jason Pither Abstract Aim, To interpret the unimodal relationship between diatom species richness and lake pH within the context of the evolutionary species pool hypothesis (SPH). We test the following primary prediction arising from the SPH: the size of the potential species pool (PSP) will increase along a gradient representing the historical commonness of different pH environments (pH commonness). To do this we assume that the present-day spatial dominance of near-neutral pH conditions compared with acidic and alkaline conditions reliably mimics the relative spatial availabilities of historical pH conditions among freshwater lakes. We also determine whether local richness represents a constant proportion of PSP size along the pH commonness gradient. Location, Two hundred and thirty-four lakes distributed over a 405,000 km2 region of the north-eastern United States of America. Methods, Sediment diatom morphospecies lists and pH data were acquired from the US Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP) website. Using 248 morphospecies that occurred in at least 10 of the 234 lakes, four different measures of PSPs were calculated along the pH gradient. Local species richness was equated with the number of species occurring within the lake. Alpha diversity was equated with the average species richness of lakes with similar pH values. A combination of statistical methods were employed, including correlations, quadratic regression and piecewise regression. Results, PSP size increased significantly with pH commonness for all four measures of PSP size, thus supporting the primary prediction of the evolutionary SPH. Local richness comprised a larger proportion of the PSP within acidic lakes than within circumneutral lakes. Alpha diversity and lake species richness both increased significantly with pH commonness, but the former did so in a two-step fashion. We test and reject several alternative contemporary time-scale explanations for our findings. Main Conclusions, Our findings are consistent with the hypothesis that diatom taxonomic richness is presently lower within acidic and highly alkaline lakes than in circumneutral lakes owing to the limited opportunity in space and/or time for the evolution of suitably adapted species. Whereas ecological processes can explain why certain species are excluded from particular habitats, e.g. acidic lakes, they cannot account for why so few species are adapted to those habitats in the first place. [source] Broad-scale environmental response and niche conservatism in lacustrine diatom communitiesGLOBAL ECOLOGY, Issue 5 2010Joseph R. Bennett ABSTRACT Aim, (1) To resolve theoretical debates regarding the role of environment versus dispersal limitation, the conservatism of niches across distances and the prevalence of environmental specialists in diatom communities. (2) To provide guidance on the use of diatom communities and other microbial analogues to analyse ecological response to environmental change. Location, Eight hundred and ninety-one lakes in five regional datasets from north-western Europe and four regional datasets from north-eastern North America. Methods, Lacustrine diatom communities were analysed at three scales: inter-continental, intra-continental and regional. Nested partial redundancy analyses (RDAs) were used to determine spatial versus environmental components of community variation. Weighted-averaging (WA) regression and calibration, as well as logistic and quadratic regressions, were used to detect niche conservatism and the prevalence of environmental specialists. Results, Community patterns indicate that dispersal limitation acts predominantly at the inter-continental scale, while at the regional (less than c. 1,000,000 km2) scale, a single environmental variable (pH) explains more than five times the community variation as spatial (dispersal-related) variables. In addition, pH niche components appear to be conserved at the inter-continental scale, and environmental specialization does not impose relative rarity, as specialists apparently readily disperse to suitable environments. Main conclusions, Analysis at multiple scales is clearly important in determining the influences of community variation. For diatom communities, dispersal limitation acts most strongly at the broadest scales, giving way to environment at the scales considered by most analyses. The availability of a wide variety of propagules with consistent niches across regions indicates that diatom communities reflect the succession of taxa according to local environmental conditions, rather than disequilibrium with the environment or adaptation of local populations. While multi-scale analyses must be undertaken for other groups to resolve debates over community drivers and determine appropriate scales for prediction, for diatoms (and probably other microbial communities), responses to environmental change can be inferred using analogue datasets from large geographic areas. [source] Lycopene content differs among red-fleshed watermelon cultivars,JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 10 2001Penelope Perkins-Veazie Abstract Lycopene, a carotenoid, has antioxidant properties that may reduce the incidence of certain cancers. Watermelon (Citrullus lanatus (Thunb) Matsum & Nakai) is a natural source of lycopene, with a reported average content of 48.7,µg,g,1 fresh weight based on samples taken from retail produce. This study demonstrated the variability of lycopene content in 11 red-fleshed watermelon cultivars grown at one location, representing seedless, open-pollinated and hybrid types, and in commercially shipped hybrid and seedless melons, representing seasonal production periods. Tristimulus colorimeter a* and chroma values were positively correlated with lycopene values, but linear or quadratic regressions of colorimeter data against lycopene values were not significant. Tristimulus colorimeter readings from cut melons were compared to amounts of lycopene extracted from the same melons. Lycopene content varied widely among cultivars, with four cultivars having mean values greater than 65.0,µg,g,1 fresh weight. Seedless types sampled tended to have higher amounts of lycopene (>50.0,µg,g,1 fresh weight) than seeded types. Watermelon lycopene content changed for some cultivars with production season. Published in 2001 for SCI by John Wiley & Sons, Ltd [source] Effect of dietary protein levels on growth performance and whole body composition of summerling and winterling spotted barbel (Hemibarbus maculates Bleeker)AQUACULTURE NUTRITION, Issue 4 2010J.-M. CHEN Abstract Six test diets with protein levels varying from 250 to 500 g kg,1 were fed to six triplicate groups of summerling (initial weight: 1.56 g) and seven test diets with protein levels varying from 200 to 500 g kg,1 were fed to seven triplicate groups of winterling (initial weight: 9.49 g) for 8 weeks. Weight gain (WG) and feed efficiency (FE) of summerling significantly increased with increasing dietary protein levels from 250 to 350 g kg,1 and slightly declined, but without statistical significance at a dietary protein level of 400 g kg,1, then further significantly decreased with increasing protein levels to 450 and 500 g kg,1; WG of winterling increased significantly with increasing dietary protein levels from 200 to 300 g kg,1 (P < 0.05), and above this level, WG had a tendency to decrease with increasing dietary protein levels. Winterling fed diets with 300 and 400 g kg,1 of dietary protein had significantly higher FE than those fed other diets. WG data analysis by quadratic regressions showed that the optimum dietary protein levels required for the maximum growth of summerling and winterling were 374 and 355 g kg,1 of dry diet respectively. Protein efficiency ratio of both summerling and winterling negatively correlated with levels of dietary protein. The whole body moisture, protein, lipid and ash of summerling after being fed various test diets for 8 weeks were significantly different among treatments (P < 0.05). The whole body moisture and fat of winterling were also significantly affected by dietary protein levels (P < 0.05), while the whole body protein and ash of winterling were not (P > 0.05). [source] | ||||||||||