Optimal Size (optimal + size)

Distribution by Scientific Domains


Selected Abstracts


EMPIRICAL EVIDENCE FOR AN OPTIMAL BODY SIZE IN SNAKES

EVOLUTION, Issue 2 2003
Scott M. Boback
Abstract The concept of optimal size has been invoked to explain patterns in body size of terrestrial mammals. However, the generality of this phenomenon has not been tested with similarly complete data from other taxonomic groups. In this study we describe three statistical patterns of body size in snakes, all of which indicate an optimal length of 1.0 m. First, a distribution of largest body lengths of 618 snake species had a single mode at 1.0 m. Second, we found a positive relationship between the size of the largest member of an island snake assemblage and island area and a negative relationship between the size of the smallest member of an island snake assemblage and island area. Best-fit lines through these data cross at a point corresponding to 1.0 m in body length, the presumed optimal size for a one-species island. Third, mainland snake species smaller than 1.0 m become larger on islands whereas those larger than 1.0 m become smaller on islands. The observation that all three analyses converge on a common body size is concordant with patterns observed in mammals and partial analyses of four other disparate animal clades. Because snakes differ so strikingly from mammals (ectotherms, gape-limited predators, elongate body shape) the concordant patterns of these two groups provide strong evidence for the evolution of an optimal body size within independent monophyletic groups. However, snakes differ from other taxonomic groups that have been studied in exhibiting a body size distribution that is not obviously skewed in either direction. We suggest that idiosyncratic features of the natural history of ectotherms allow relatively unconstrained distributions of body size whereas physiological limitations of endotherms constrain distributions of body size to a right skew. [source]


Cultural Districts, Property Rights and Sustainable Economic Growth

INTERNATIONAL JOURNAL OF URBAN AND REGIONAL RESEARCH, Issue 1 2002
Walter Santagata
The purpose of this article is to analyse the economic properties as well as the institutions governing the start-up and evolution of cultural districts. The first part of the article reviews the relationships between culture, viewed as an idiosyncratic good, and the theory of industrial districts. The second part comprises a critical discussion of four models of cultural districts: the industrial cultural district (mainly based on positive externalities, localized culture and traditions in ,arts and crafts'); the institutional cultural district (chiefly relying on the assignment of property rights); the museums cultural district (based on network externalities and the search for optimal size); and the metropolitan cultural district (based on communication technologies, performing arts and electronic trade). The assignment of intellectual property rights to local idiosyncratic cultural goods seems to be the most significant way to differentiate among cultural districts. The final section discusses a possible convergence of all district models towards the institutional district, based on the creation of a system of property rights as a means to protect localized production. Cet article tente d'analyser les propriétés économiques et les institutions qui régissent la création et l'évolution de districts culturels. La première partie étudie les relations entre la culture , vue comme un bien idiosyncrasique , et la théorie des districts industriels. La deuxième partie est un débat critique sur quatre modèles de districts culturels: le district culturel industriel (basé essentiellement sur des externalités positives, des cultures et traditions artisanales locales), le district culturel institutionnel (s'appuyant principalement sur l'attribution de droits de propriété), le district culturel des musées (fondé sur des effets d'entraînement en réseau et la recherche d'une taille optimale), et le district culturel métropolitain (basé sur les technologies de communication, des représentations artistiques et le commerce électronique). L'attribution de droits de propriété intellectuelle sur des biens culturels idiosyncrasiques locaux semble être la meilleure manière de différencier les districts culturels. La dernière partie de l'article examine une convergence possible de tous les modèles de district vers le district institutionnel, en s'appuyant sur la création d'un système de droits de propriété comme moyen de protection d'une production locale. [source]


The island rule and the evolution of body size in the deep sea

JOURNAL OF BIOGEOGRAPHY, Issue 9 2006
Craig R. McClain
Abstract Aim, Our goal is to test the generality of the island rule , a graded trend from gigantism in small-bodied species to dwarfism in large-bodied species , in the deep sea, a non-insular but potentially analogous system. Location, Shallow-water and deep-sea benthic habitats in the western Atlantic Ocean from the North to South Poles. Methods, We conducted regression analyses of body size of deep-sea gastropods species relative to their shallow-water congeners using measurements from the Malacolog ver. 3.3.3 database. Results, Our results indicate that, consistent with the island rule, gastropod genera with small-bodied, shallow-water species have significantly larger deep-sea representatives, while the opposite is true for genera that are large-bodied in shallow water. Bathymetric body size clines within the deep sea are also consistent with predictions based on the island rule. Main conclusions, Like islands, the deep sea is characterized by low absolute food availability, leading us to hypothesize that the island rule is a result of selection on body size in a resource-constrained environment. The body size of deep-sea species tends to converge on an optimal size for their particular ecological strategy and habitat. [source]


Sexually antagonistic selection on primate size

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2002
P. Lindenfors
Abstract Male intrasexual selection in haplorhine primates has previously been shown to increase male size and to a lesser degree also female size. I address the following questions: (1) why does female size increase when the selection is on males, and (2) why does female size not increase to the same extent as that of males. The potential for correlational selection on females through increased resource competition was analysed with independent contrasts analyses. No such effect was found, nor did matched pairs comparisons reveal females to increase in size because of selection to bear larger male offspring. Instead further matched pairs analyses revealed higher female postpartum investment, as indicated by a longer lactation period, in more sexually selected species, also after correcting for body weight. Concerning the second question, independent contrast analyses showed that large size has had negative effects on female reproductive rate across the primate order. Matched-pairs analyses on haplorhines revealed that females of species in more polygynous clades have lower reproductive rates than females of species in less polygynous clades. This is also true after the effects of body weight are removed. These results, both when correcting for body weight and when not, suggest that sexual selection has shifted female size from one favouring female lifetime fecundity to one favouring male success in competition. This depicts antagonistic selection pressures on female size and a trade-off for females between the ecologically optimal size of their foremothers and the larger size that made their forefathers successful. [source]


Credit Spreads and Monetary Policy

JOURNAL OF MONEY, CREDIT AND BANKING, Issue 2010
VASCO CÚRDIA
credit frictions; interest rate rules; Taylor rules We consider the desirability of modifying a standard Taylor rule for interest rate policy to incorporate adjustments for measures of financial conditions. We consider the consequences of such adjustments for the way policy would respond to a variety of disturbances, using the dynamic stochastic general equilibrium model with credit frictions developed in Cúrdia and Woodford (2009a). According to our model, an adjustment for variations in credit spreads can improve upon the standard Taylor rule, but the optimal size of adjustment depends on the source of the variation in credit spreads. A response to the quantity of credit is less likely to be helpful. [source]


Broadband circularly polarized inverted-L patch antenna

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2003
Che-Wei Su
Abstract An innovative design of a corner-truncated inverted-L patch antenna for achieving circular polarization (CP) operation over a wide bandwidth is presented. The antenna has a thick air-layer substrate; however, it can be easily excited using a probe feed with a short probe pin. CP operation is obtained by selecting an optimal size of the truncated corners, and good impedance matching over a wide bandwidth is obtained by using a beveling technique on the vertical portion of the inverted-L patch. For a prototype constructed for wireless local area network (WLAN) operation in the 2.4-GHz band (2.4,2.484 GHz), the obtained CP bandwidth (3-dB axial ratio) reaches about 7%, and the measured antenna gain is about 8.0 dBi across the CP bandwidth. Details of the antenna design and the experimental results are presented. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 134,136, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10995 [source]


Inferring adaptation within shape diversity of the humerus of subterranean rodent Ctenomys

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2010
FRANCISCO STEINER-SOUZA
In subterranean rodents of the genus Ctenomys, excavation activity can be carried out with the claws and forelimbs (scratch-digging) as well as with the skull and incisor teeth (skull-tooth digging). Within the forelimb myoskeletal system, the humerus is a main bone concentrating a large number of muscles and bearing tensions during excavation. The genus Ctenomys is considered primarily a scratch-digger and secondarily a skull-tooth digger. We analysed the humerus (N = 165) of four species of Ctenomys from southern Brazil, in areas ranging from the soft soils of the first lines of coastal dunes (Ctenomys flamarioni, Ctenomys minutus), through the sandy fields of the coastal plains (Ctenomys minutus, Ctenomys lami), on to the hard soils of the southern pampas ,gaúchos' fields (Ctenomys torquatus). The differences in the form (size + shape) were quantified using geometric morphometrics methods and interpreted in the light of myological descriptions. As expected from a phylogenetic and ecological point of view, C. flamarioni had the most divergent shape and larger size among the species analysed, showing a more slender humerus, especially in the head region, than C. lami, C. minutus, and C. torquatus. Crossing the osteology data with the qualitative observations of the musculature, it was possible to detect large differences in the proximal portion of the humerus that could be related to the insertion of important extension muscles of the pectoral,shoulder joints, which could increase force. The comparison of shape differences between the three closely-related species (C. lami, C. minutus, and C. torquatus) revealed unexpected patterns because C. lami was the species phenetically more distant from C. flamarioni and not C. torquatus as expected from ecological data and phylogenetic relationships. A two-step adaptive path to humeral shapes better fit to digging is postulated where the deltoid crest and epicondylar crest increases precede an articular surface area increase. The absence of sexual dimorphism in C. torquatus is discussed with regard to the optimal size required to dig in hard soils. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 353,367. [source]


Why are species' body size distributions usually skewed to the right?

FUNCTIONAL ECOLOGY, Issue 4 2002
Jan Koz, owski
Summary 1.,Species' body size distributions are right-skewed, symmetric or left-skewed, but right-skewness strongly prevails. 2.,Skewness changes with taxonomic level, with a tendency to high right-skewness in classes and diverse skewness in orders within a class. Where the number of lower taxa allows for analysis, skewness coefficients have normal distributions, with the majority of taxa being right-skewed. 3.,Skewness changes with geographical scale. For a broad range, distributions in a class are usually right-skewed. For a narrower scale, distributions remain right-skewed or become symmetric or even close to uniform. 4.,The prevailing right-skewness of species' body size distributions is explained with macroevolutionary models, the fractal character of the environment, or body size optimization. 5.,Macroevolutionary models assume either size-biased speciation and extinction, or the existence of a constraint on small size. Macroevolutionary mechanisms seem insufficient to explain the pattern of species' body size distributions, but they may operate together with other mechanisms. 6.,Optimization models assume that directional and then stabilizing selection works after speciation events. There are two kinds of optimization approaches to study species' body size distributions. Under the first approach, it is assumed that a single energetic optimum exists for an entire taxon, and that species are distributed around this optimum. Under the second approach, each species has a separate optimum, and the species' body size distribution reflects the distribution of optimal values. 7.,Because not only energetic properties but also mortality are important in determining optimal sizes, only the second approach, that is, seeking the distribution of optimal values, seems appropriate in the context of life-history evolution. This approach predicts diverse shapes of body size distributions, with right-skewness prevailing. [source]


Size compensation in moth larvae: attention to larval instars

PHYSIOLOGICAL ENTOMOLOGY, Issue 3 2010
TOOMAS ESPERK
Environmental perturbations such as starvation and poor diet often prevent animals from attaining their optimal sizes. When the perturbation has a transient character, compensatory responses are expected in terms of faster growth or a prolonged developmental period. In the case of insect larvae, details of such responses are insufficiently known at the proximate level. Attention to responses at the level of particular larval instars should promote an understanding of insect developmental plasticity also in a more general context. To provide an instar-specific analysis of compensatory growth, larvae of the moth Orgyia antiqua (L.) are reared on inferior diet during one larval instar. Responses in growth parameters are recorded in the course of the manipulated instars, as well as at the level of the entire larval period. The negative relationship between development time and size in response to the inferior food quality, typical of the entire larval periods, is also observed within the manipulated instars taken separately. The manipulated larvae remain smaller than the larvae of the control group (significant in males only), even by the end of the subsequent instar during which all individuals are provided with superior host. In males, close to full size compensation by the time of pupation is achieved only by means of adding an extra larval instar. The inability of larvae to fully compensate during one and even two instars is considered as an indication of the presence of constraints on the within-instar growth pattern. An alternative, adaptational explanation for the incomplete compensation could be based on the cost of prolonged development period. Given the ecological context of the species' life history, such an explanation appears less likely. [source]