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Species Effects (species + effects)
Selected AbstractsSaline Drainage Water, Irrigation Frequency and Crop Species Effects on Some Physical Properties of SoilsJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 1 2001Y. A. Al-Nabulsi This field study evaluated the effects of water quality, irrigation frequency and crop species on some physical properties of soils. The experiment had a split-split-plot design, with three irrigation water qualities (normal water, drainage water and a 1 : 1 mixture of freshwater and drainage water) as the main treatments, two irrigation frequencies (at 7- and 14-day intervals) as the subtreatments and two crops (barley and alfalfa) as the subsubtreatments. The soil infiltration rate was highest in the barley plot receiving freshwater irrigation at weekly intervals. The lowest soil infiltration rate was found in alfalfa plots receiving saline irrigation water at 14-day intervals. Bulk density and proportions of micropores [pore radius (r) < 1.4 µm] were higher and the proportion of macropores (r > 14.4 µm) was lower in barley than in alfalfa. Saline irrigation caused the greatest decrease in total porosity. The soil infiltration rate was higher with more frequent irrigation, and was highest in alfalfa plots receiving freshwater irrigation. The decrease in soil bulk density and infiltration rate was greater with saline drainage water, irrespective of the crop grown and the irrigation frequency. Salzhaltiges Drainagewasser, Bewässerungshäufig-keit und Kulturpflanzenarten mit Wirkung auf einige physikalische Eigenschaften des Bodens Eine Felduntersuchung wurde vorgenommen, um dem Einfluss der Wasserqualität, der Bewässerungshäufigkeit und Kulturpflanzenarten auf einige physikalische Eigenschaften von Böden zu untersuchen. Die Infiltrationrate mit Frischwasser in wöchentlichen Abständen unter Gerste war hoch. Eine Behandlung mit Salzwasser in 14 tägigen Abständen unter Luzerne zeigte eine geringere Infiltrationsrate des Bodens. Bodendichte und der Anteil der Mikroporen (Poren mit einem Radius von r < 1,4 mm) waren größer und der Anteil der Makroporen (r > 14,4 mm) war unter Gerste geringer. Bewässerung mit Salzwasser verursachte die stärkste Abnahme in der Gesamtporosität. Die Infiltrationsrate des Bodens nahm mit der Häufigkeit der Bewässerung zu und zeigte den höchsten Wert bei Luzerne und einer Frischwasserbewässerung. Die Abnahme in der Bodendichte und der Infiltrationseigenschaften waren bei Salzwasserdrainage unabhängig von der Kulturpflanzenart und der Bewässerungshäufigkeit höher. [source] The effects of preservation on fish tissue stable isotope signaturesJOURNAL OF FISH BIOLOGY, Issue 6 2006B. Kelly The effects of formalin and ethanol preservation on the ,13C and ,15N isotope signatures of Arctic charr Salvelinus alpinus muscle tissue were examined. The lipid content of the tissue samples studied ranged from 3·6 to 6·1% and was not correlated with the magnitude of observed isotopic shifts in preserved samples. Ethanol and formalin significantly depleted and enriched, respectively, the ,13C isotope signatures of preserved tissues when compared to control samples. Ethanol did not significantly enrich ,15N signatures in comparison to controls, whereas formalin did. A meta-analysis of multiple species effects further demonstrated significant preservation effects in fish tissue. Statistical analysis of data obtained by correcting preserved tissue isotope signatures with literature, bootstrapped or meta-analysis derived correction factors demonstrated significant differences between corrected and control sample isotope signatures or failure to produce a unity slope when the data sets were regressed against one another. Species-specific, bootstrapped linear correction models resulted in no such errors. Results suggest that species-specific correction methods should be used for fishes because of the known wide variation in fish tissue lipid content and composition. Accordingly, the use of pilot studies will be required to develop correction factors that properly adjust for preservation effects when interpreting temporal patterns in historic analyses of food webs. [source] Effects of dietary protein and lipid level, and water temperature, on the post-feeding oxygen consumption of Atlantic cod and haddockAQUACULTURE RESEARCH, Issue 2 2010Juan C Pérez-Casanova Abstract Tank respirometry was used to study the interactive effects of protein:lipid level (55%:11% vs. 42%:16%; both diets isoenergetic) and temperature (11, 6 and 2 °C) on the magnitude and duration of specific dynamic action (SDA) in juvenile Atlantic cod and haddock. The protein:lipid level did not affect any measured variable. However, numerous temperature and species effects were observed. For example, although the maximum post-feeding oxygen consumption (30,50% above routine metabolic rate; RMR) and SDA duration (,55,85 h; SDADUR) were not affected by temperature, SDADUR g,1 of food increased from 11 to 2 °C (from ,3 to 12 h g food,1). While absolute SDA (mg O2) decreased by ,60,65% in cod and ,75% in haddock from 11 to 2 °C, due to a concomitant decrease in food consumption from ,2.0% to 0.6% body mass, SDA comprised between 3.3% and 5.2% of the dietary energy content at all temperatures. Finally, RMR at 11 and 2 °C and SDADUR at 2 °C were 25,35% and 25% greater in cod, respectively, as compared with haddock. These results suggest that feeding reduced protein diets at low water temperatures is unlikely to improve the growth of these species. [source] Occupancy frequency distributions: patterns, artefacts and mechanismsBIOLOGICAL REVIEWS, Issue 3 2002MELODIE A. McGEOCH ABSTRACT Numerous hypotheses have been proposed to explain the shape of occupancy frequency distributions (distributions of the numbers of species occupying different numbers of areas). Artefactual effects include sampling characteristics, whereas biological mechanisms include organismal, niche-based and metapopulation models. To date, there has been little testing of these models. In addition, although empirically derived occupancy distributions encompass an array of taxa and spatial scales, comparisons between them are often not possible because of differences in sampling protocol and method of construction. In this paper, the effects of sampling protocol (grain, sample number, extent, sampling coverage and intensity) on the shape of occupancy distributions are examined, and approaches for minimising artefactual effects recommended. Evidence for proposed biological determinants of the shape of occupancy distributions is then examined. Good support exists for some mechanisms (habitat and environmental heterogeneity), little for others (dispersal ability), while some hypotheses remain untested (landscape productivity, position in geographic range, range size frequency distributions), or are unlikely to be useful explanations for the shape of occupancy distributions (species specificity and adaptation to habitat, extinction,colonization dynamics). The presence of a core (class containing species with the highest occupancy) mode in occupancy distributions is most likely to be associated with larger sample units, and small homogenous sampling areas positioned well within and towards the range centers of a sufficient proportion of the species in the assemblage. Satellite (class with species with the lowest occupancy) modes are associated with sampling large, heterogeneous areas that incorporate a large proportion of the assemblage range. However, satellite modes commonly also occur in the presence of a core mode, and rare species effects are likely to contribute to the presence of a satellite mode at most sampling scales. In most proposed hypotheses, spatial scale is an important determinant of the shape of the observed occupancy distribution. Because the attributes of the mechanisms associated with these hypotheses change with spatial scale, their predictions for the shape of occupancy distributions also change. To understand occupancy distributions and the mechanisms underlying them, a synthesis of pattern documentation and model testing across scales is thus needed. The development of null models, comparisons of occupancy distributions across spatial scales and taxa, documentation of the movement of individual species between occupancy classes with changes in spatial scale, as well as further testing of biological mechanisms are all necessary for an improved understanding of the distribution of species and assemblages within their geographic ranges. [source] The evolution of rewards: seed dispersal, seed size and elaiosome sizeJOURNAL OF ECOLOGY, Issue 3 2006WILL EDWARDS Summary 1We examine the relationship between the reward offered to ants to disperse seeds (elaiosome size) and seed size, and the possible mechanisms that may generate this relationship in Australian plant species. 2We used seed and elaiosome sizes from our own data set containing 87 Acacia species, supplemented with 22 species from a previously published data set, and 98 ,Other species' from 51 genera in 25 families, also from published data. 3The relationship between ln(elaiosome size) and ln(seed size) was determined using standard major axis (SMA) regression for both data sets. For the Other data set we also determined the relationship among species independent of the differences between genera, among genera independent of the differences between families, among genera and among families. We used SMA to test for differences in slopes between groups. 4We found a significant common slope amongst all subsets of the larger data set. The estimated common slope and the 95% confidence interval for the relationship between ln(elaiosome size) and ln(seed size) across all data sets fell above one (1.24, 95%CI = 1.17,1.32), suggesting positive allometry. Slopes were also significantly positive and strikingly similar between the Acacia species data set and the Other species data sets. Similar positive allometry was shown in the ,other' species data set among genera and families, and among species independent of genus means (,species effects'). 5Significant and consistent relationships between taxonomic levels, independent of relationships at other levels, along with significant relationships at the species level, and similarity of slopes, suggest independent convergence towards an underlying functional relationship that has persisted over long evolutionary periods. Our results therefore suggest that ants have been agents of selection on seed traits. 6Such a functional relationship might result from a trade-off in ant foraging behaviour between the benefit of the reward (elaiosome) and the cost of the dispersal (determined by seed size). Slopes > 1 would then suggest that ants need more than proportionally larger rewards to remove larger seeds. [source] | |||||||||||||