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Scale Dependent (scale + dependent)

Distribution by Scientific Domains

Life Sciences	40%

Selected Abstracts

COMPARING STRENGTHS OF DIRECTIONAL SELECTION: HOW STRONG IS STRONG?

EVOLUTION, Issue 10 2004
Joe Hereford
Abstract The fundamental equation in evolutionary quantitative genetics, the Lande equation, describes the response to directional selection as a product of the additive genetic variance and the selection gradient of trait value on relative fitness. Comparisons of both genetic variances and selection gradients across traits or populations require standardization, as both are scale dependent. The Lande equation can be standardized in two ways. Standardizing by the variance of the selected trait yields the response in units of standard deviation as the product of the heritability and the variance-standardized selection gradient. This standardization conflates selection and variation because the phenotypic variance is a function of the genetic variance. Alternatively, one can standardize the Lande equation using the trait mean, yielding the proportional response to selection as the product of the squared coefficient of additive genetic variance and the mean-standardized selection gradient. Mean-standardized selection gradients are particularly useful for summarizing the strength of selection because the mean-standardized gradient for fitness itself is one, a convenient benchmark for strong selection. We review published estimates of directional selection in natural populations using mean-standardized selection gradients. Only 38 published studies provided all the necessary information for calculation of mean-standardized gradients. The median absolute value of multivariate mean-standardized gradients shows that selection is on average 54% as strong as selection on fitness. Correcting for the upward bias introduced by taking absolute values lowers the median to 31%, still very strong selection. Such large estimates clearly cannot be representative of selection on all traits. Some possible sources of overestimation of the strength of selection include confounding environmental and genotypic effects on fitness, the use of fitness components as proxies for fitness, and biases in publication or choice of traits to study. [source]

An econometric analysis of regional adoption patterns of Bt maize in Germany

AGRICULTURAL ECONOMICS, Issue 3-4 2010
Nicola Consmüller
Bt maize; Genetically modified organisms (GMO); Germany; Panel data analysis Abstract In this study, our goal is to identify and explain the underlying factors that drive regional adoption of Bt maize MON810 in Germany. Since regional differences cannot be explained by the occurrence of the target pest alone, we assume that under the given regulatory framework for genetically modified (GM) crop production in Germany, farm structures as well as the sociopolitical environment have also influenced regional adoption rates during the past years. Following a description of the relevant legal and economic framework in Germany, we develop theoretical hypotheses for regional variation in Bt maize adoption and test them econometrically with unique data at the federal state (Laender) and county (Landkreis) level. According to our analysis at the federal state level, the maize acreage per farm is the main driver of Bt maize adoption. In addition, there are signs that public opposition to GM cultivation as measured by membership in the German Friends of the Earth association significantly dampens GM cultivation. At the level of Brandenburg counties, the regional infestation frequency of the European Corn Borer, the target pest of Bt-Maize, is the major determinant of adoption. Although Bt maize is a scale-neutral technology for controlling damages caused by the Corn Borer, additional fixed costs due to regulation make the technology scale dependent. [source]

WIDTH OF STREAMS AND RIVERS IN RESPONSE TO VEGETATION, BANK MATERIAL, AND OTHER FACTORS,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2004
Russell J. Anderson
ABSTRACT: An extensive group of datasets was analyzed to examine factors affecting widths of streams and rivers. Results indicate that vegetative controls on channel size are scale dependent. In channels with watersheds greater than 10 to 100 km2, widths are narrower in channels with thick woody bank vegetation than in grass lined or nonforested banks. The converse is true in smaller streams apparently due to interactions between woody debris, shading, understory vegetation, rooting characteristics, and channel size. A tree based statistical method (regression tree) is introduced and tested as a tool for identifying thresholds of response and interpreting interactions between variables. The implications of scale dependent controls on channel width are discussed in the context of stable channel design methods and development of regional hydraulic geometry curves. [source]

Scale-dependent trait correlations in a temperate tree community

AUSTRAL ECOLOGY, Issue 6 2009
K. C. BURNS
Abstract Recent investigations of relationships among plant traits have generated important insights into plant form and function. However, relationships involving leaf area, leaf shape and plant height remain poorly resolved. Previous work has also focused on correlations between average trait values for individual species. It is unclear whether similar relationships occur within species. We searched for novel plant trait correlations by comparing leaf area, leaf circularity, specific leaf area (SLA) and plant height among 16 common woody plant species from a temperate forest in New Zealand. Analyses were conducted both within species (intra-specifically) and among species (inter-specifically) to determine whether trait correlations were scale dependent. Leaf area was unrelated to other leaf traits inter-specifically. However, leaf area declined with plant height and increased with SLA intra-specifically. Leaf circularity decreased with plant height inter-specifically, but increased with plant height intra-specifically. SLA increased with plant height both inter- and intra-specifically. Leaf circularity increased with SLA inter-specifically, but decreased with SLA intra-specifically. Overall results showed that leaf shape, SLA and plant height are interrelated. However, intra-specific relationships often differed substantially from inter-specific relationships, suggesting that the processes shaping relationships between this suite of plant traits are scale-dependent. [source]

Novel Process Windows , Gate to Maximizing Process Intensification via Flow Chemistry

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2009
V. Hessel
Abstract Driven by the economics of scale, the size of reaction vessels as the major processing apparatus of the chemical industry has became bigger and bigger [1, 2]. Consequently, the efforts for ensuring mixing and heat transfer have also increased, as these are scale dependent. This has brought vessel operation to (partly severe) technical limits, especially when controlling harsh conditions, e.g., due to large heat releases. Accordingly, processing at a very large scale has resulted in taming of the chemistry involved in order to slow it down to a technically controllable level. Therefore, reaction paths that already turned out too aggressive at the laboratory scale are automatically excluded for later scale-up, which constitutes a common everyday confinement in exploiting chemical transformations. Organic chemists are barely conscious that even the small-scale laboratory protocols in their textbooks contain many slow, disciplined chemical reactions. Operations such as adding a reactant drop by drop in a large diluted solvent volume have become second nature, but are not intrinsic to the good engineering of chemical reactions. These are intrinsic to the chemical apparatus used in the past. In contrast, today's process intensification [3,12] and the new flow-chemistry reactors on the micro- and milli-scale [13,39] allow such limitations to be overcome, and thus, enable a complete, ab-initio type rethinking of the processes themselves. In this way, space-time yields and the productivity of the reactor can be increased by orders of magnitude and other dramatic performance step changes can be achieved. A hand-in-hand design of the reactors and process re-thinking is required to enable chemistry rather than subduing chemistry around the reactor [40]. This often leads to making use of process conditions far from conventional practice, under harsh environments, a procedure named here as Novel Process Windows. [source]