Negative Growth (negative + growth)

Distribution by Scientific Domains

Selected Abstracts

Population ecology of cave armoured catfish, Ancistrus cryptophthalmus Reis 1987, from central Brazil (Siluriformes: Loricariidae)

E. Trajano
Abstract,,, The population ecology of Ancistrus cryptophthalmus (Reis 1987) was studied by mark,recapture technique in caves from the São Domingos karst area, State of Goiás, northeastern Brazil. Total population sizes estimated for Angélica and Passa Três Caves were 20,000 and 1000 individuals, respectively. Densities around 1.0 individuals per m2 in Angélica, Bezerra and São Vicente I Streams, and 0.6 individuals per m2 in the smaller Passa Três Stream may be considered high for cavefish standards, as well as for epigean loricariids. As expected for benthic grazers, cave catfish are highly sedentary. The distribution of size classes did not differ among caves and within the same cave throughout the studied dry seasons; on the contrary, the condition factor decreased throughout this period probably because of the progressive depletion of organic matter available as food. Low proportions of mature individuals, low growth rates (average = 0.5 mm month,1) with cases of negative growth and high longevities (8,10 years) point to a precocial lifestyle, typical of troglobitic species. [source]

Are parametric models suitable for estimating avian growth rates?

William P. Brown
For many bird species, growth is negative or equivocal during development. Traditional, parametric growth curves assume growth follows a sigmoidal form with prescribed inflection points and is positive until asymptotic size. Accordingly, these curves will not accurately capture the variable, sometimes considerable, fluctuations in avian growth over the course of the trajectory. We evaluated the fit of three traditional growth curves (logistic, Gompertz, and von Bertalanffy) and a nonparametric spline estimator to simulated growth data of six different specified forms over a range of sample sizes. For all sample sizes, the spline best fit the simulated model that exhibited negative growth during a portion of the trajectory. The Gompertz curve was the most flexible for fitting simulated models that were strictly sigmoidal in form, yet the fit of the spline was comparable to that of the Gompertz curve as sample size increased. Importantly, confidence intervals for all of the fitted, traditional growth curves were wholly inaccurate, negating the apparent robustness of the Gompertz curve, while confidence intervals of the spline were acceptable. We further evaluated the fit of traditional growth curves and the spline to a large data set of wood thrush Hylocichla mustelina mass and wing chord observations. The spline fit the wood thrush data better than the traditional growth curves, produced estimates that did not differ from known observations, and described negative growth rates at relevant life history stages that were not detected by the growth curves. The common rationale for using parametric growth curves, which compress growth information into a few parameters, is to predict an expected size or growth rate at some age or to compare estimated growth with other published estimates. The suitability of these traditional growth curves may be compromised by several factors, however, including variability in the true growth trajectory. Nonparametric methods, such as the spline, provide a precise description of empirical growth yet do not produce such parameter estimates. Selection of a growth descriptor is best determined by the question being asked but may be constrained by inherent patterns in the growth data. [source]

District-level total factor productivity in agriculture: Western Cape Province, South Africa, 1952,2002

Beatrice Conradie
Total factor productivity; Western Cape; South Africa Abstract This article measures total factor productivity (TFP) growth in Western Cape agriculture for 31 magisterial districts from 1952 to 2002 to illustrate the benefits of disaggregation compared with national TFPs. There is negative or low growth in the eastern districts and rapid growth in the western districts. The regions with substantial chicken, pigs, dairy, and, especially, export fruit production grew rapidly, whereas the sheep-dominated Karoo had negative growth. Productivity growth correlates mostly with output mix, which in turn depends on irrigation investment. A similar program will be needed at the national level if prosperity is to be extended to black smallholders who currently lack access to water and other modern infrastructure. [source]

Phases of the Canadian business cycle

Philip M. Bodman
In this paper we contrast a number of univariate models of Canadian GDP. Our preferred models are used to provide a business cycle chronology for Canada, which is compared with some existing, more judgmentally determined chronologies. We find that a simple, ,two quarters of negative growth' rule for determining recession dates is the most similar to our chronology. We also find that the most recent recession in Canada was unique in both its length and the slow speed of recovery. JEL Classification: C22, C51, C52, E32 Phases du cycle d'affaires au Canada. Dans ce mémoire, les auteurs contrastent un certain nombre de modèles du PIB canadien. Les modèles préférés sont utilisés pour définir une chronologie des cycles économiques du Canada qu'on peut comparer avec d'autres chronologies existantes basées davantage sur le jugement. On découvre que la règle "deux trimestres de croissance négative" est celle qui se rapproche le plus de la chronologie proposée quand il s'agit de définir les dates de récession. On découvre aussi que la récente récession canadienne a été unique tant par sa durée que par la lenteur avec laquelle la reprise subséquente s'est amorcée. [source]