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Ratio Variation (ratio + variation)

Distribution by Scientific Domains
Life Sciences87%

Kinds of Ratio Variation

  • sex ratio variation
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    Selected Abstracts

    Timing of foetal growth spurts can explain sex ratio variation in polygynous mammals

    ECOLOGY LETTERS, Issue 1 2000
    M.C. Forchhammer
    The prediction from sex ratio theory that natural selection on sexually dimorphic mammals should favour an excess of male offspring only when mothers are in good condition, has been tested extensively but with little consistency in results. Although recent studies have shown that environmental variations may cause some of the discrepancy, there have also been reports of contrasting sex ratios under similar environmental settings. Here it is suggested that variation in timing of environmental stress and sex-specific differences in foetal growth pattern in relation to maternal condition, may explain such seeming contradictions in sex ratio variation of polygynous mammals. [source]

    Existing theories do not explain sex ratio variation at birth in monomorphic roe deer (Capreolus capreolus)

    INTEGRATIVE ZOOLOGY (ELECTRONIC), Issue 1 2007
    Stefan Jacob VREUGDENHIL
    Abstract The phenomenon of skewed sex ratios at birth has been reported in many ungulate species. So far, no consistent trend has emerged for roe deer (Capreolus capreolus), because male-biased, female-biased and equal sex ratios at birth have all been found. Nevertheless, both the Trivers-Willard hypothesis and the theory of local resource competition have gained support. Despite the great number of studies carried out regarding the ecology of roe deer, too many aspects remain unclear, and contradictory results have been produced with respect to several crucial elements. Without further research, the discussion on which theory applies will therefore remain inconclusive. We put forward the argument that eventually the theories of Trivers-Willard and local resource competition can be considered as being not essentially different. After all, both theories explain the observed skewed sex ratios as being due to the effect of the progeny's sex on the mother's body condition and hence her reproductive success in subsequent years. Furthermore, neither theory is likely to prove to be suitable for roe deer, as several assumptions are unlikely to be met. In roe deer, skewed ratios probably only have a temporal character. As a matter of fact, several observations of skewed sex ratios in birds and mammals did not withstand the accumulation of further data, as sex ratios that were initially believed to be biased turned out to be equal in the long term. This is likely to be the case in roe deer as well. We hypothesize that roe deer, as r-strategists, will produce as many offspring as possible, regardless of sex. [source]

    Causes and consequences of adaptive seasonal sex ratio variation in house sparrows

    JOURNAL OF ANIMAL ECOLOGY, Issue 5 2006
    ARILD HUSBY
    Summary 1Here we examine how sex ratio variation in house sparrow broods interacts with other demographic traits and parental characteristics to improve the understanding of adaptive significance and demographic effects on variation in sex ratio. 2The sex ratio in complete broods did not deviate significantly from parity (54·9% males). 3There was sex-specific seasonal variation in the probability of recruitment. Male nestlings that hatched late in the breeding season had larger probability of surviving than early hatched males. 4An adaptive adjustment of sex ratio should favour production of an excess of males late in the breeding season. Accordingly, the proportion of male offspring increased throughout the breeding season. 5A significant nonlinear relationship was present between sex ratio and age of the female. However, there was no relationship between parental phenotype and standardized hatch day that could explain the observed seasonal change in sex ratio. 6The sex-specific number of offspring recruited by a pair to subsequent generations was closely related to the brood sex ratio. 7These results indicate an adaptive adjustment of sex ratio to seasonal variation in environmental conditions that affects the offspring fitness of the two sexes differently. Our results also suggest that such a sex ratio variation can strongly influence the demography and structural composition of small passerine populations. [source]

    Intra-lake stable isotope ratio variation in selected fish species and their possible carbon sources in Lake Kyoga (Uganda): implications for aquatic food web studies

    AFRICAN JOURNAL OF ECOLOGY, Issue 3 2010
    Dismas Mbabazi
    Abstract The stable isotopes of nitrogen (,15N) and carbon (,13C) provide powerful tools for quantifying trophic relationships and carbon flow to consumers in food webs; however, the isotopic signatures of organisms vary within a lake. Assessment of carbon and nitrogen isotopic signatures in a suite of plants, invertebrates, and fishes in Lake Kyoga, indicated significant variation between two sites for ,13C (paired t = 6.305; df = 14, P < 0.001 and ,15N paired t = 1.292; df = 14; P < 0.05). The fish fauna in Bukungu was generally more 13C enriched (mean ,13C = ,16.37 ± 1.64,) than in Iyingo (mean ,13C = ,20.80 ± 2.41,) but more ,15N depleted (mean ,15N = 5.57 ± 0.71,) than in Iyingo (mean ,15N = 6.92 ± 0.83,). The simultaneous shifts in phytoplankton and consumer signatures confirmed phytoplankton as the major source of carbon for the food chain leading to fish. Limited sampling coverage within lakes may affect lake wide stable isotope signatures, and the same error is transferred into trophic position estimation. Consideration of potential intra-lake spatial variability in isotope ratios and size is essential in evaluating the spatial and trophic structure of fish assemblages. Résumé Les isotopes stables d'azote (,15N) et de carbone (,13C) sont des outils intéressants pour quantifier les relations trophiques et le flux de carbone vers les consommateurs de chaînes alimentaires; cependant, la signature isotopique des organismes varie au sein d'un même lac. L'évaluation des signatures isotopiques du carbone et de l'azote dans une suite de plantes, d'invertébrés et de poissons du lac Kyoga indiquait une variation significative entre deux sites pour ,13C (test t apparié = 6.305; df = 14; P < 0.05). La faune piscicole de Bukungu était généralement plus enrichie en ,13C (moyenne de ,13C = ,16.37 ± 1.64,) qu'à Iyingo (moyenne de ,13C = ,20.80 ± 2.41,) mais plus dépourvue de ,15N (moyenne de ,15N = 5.57 ± 0.71,) qu'Inyingo (moyenne de ,15N = 6.92 ± 0.83,). Les glissements simultanés des signatures du phytoplancton et des consommateurs confirmaient que le phytoplancton est la source principale de carbone de la chaîne alimentaire qui aboutit aux poissons. Une couverture limitée de l'échantillonnage dans les lacs peut affecter la signature des isotopes stables de tout le lac, et cette même erreur est reportée dans l'estimation de la situation trophique. Il est essentiel de tenir compte de la variabilité spatiale possible des taux et de la taille des isotopes dans les lacs lorsque l'on évalue la structure spatiale et trophique des assemblages de poissons. [source]

    Maternal age is a predominant determinant of progeny sex ratio variation in ungulates: a reply to Hewison et al.

    OIKOS, Issue 3 2003
    D. Saltz
    No abstract is available for this article. [source]

    Solute transport through a deforming porous medium

    INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7 2002
    Glen P. Peters
    Abstract Solute transport through a porous medium is typically modelled assuming the porous medium is rigid. However, many applications exist where the porous medium is deforming, including, municipal landfill liners, mine tailings dams, and land subsidence. In this paper, mass balance laws are used to derive the flow and transport equations for a deforming porous medium. The equations are derived in both spatial and material co-ordinate systems. Solute transport through an engineered landfill liner is used as an illustrative example to show the differences between the theory for a rigid porous medium, and small and large deformation analysis of a deforming porous medium. It is found that the large deformation model produces shorter solute breakthrough times, followed by the small deformation model, and then the rigid porous medium model. It is also found that it is important to include spatial and temporal void ratio variations in the large deformation analysis. It is shown that a non-linear large deformation model may greatly reduce the solute breakthrough time, compared to a standard transport analysis typically employed by environmental engineers. Copyright © 2002 John Wiley & Sons, Ltd. [source]