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Main Hypotheses (main + hypothesis)
Selected AbstractsBooms and Busts: Consumption, House Prices and ExpectationsECONOMICA, Issue 301 2009ORAZIO P. ATTANASIO Over much of the past 25 years, house price and consumption growth have been closely synchronized. Three main hypotheses for this have been proposed: increases in house prices raise household wealth and so their consumption; house price growth reduces credit constraints by increasing the collateral available to homeowners; and house prices and consumption are together influenced by common factors. Using microeconomic data, we find that the relationship between house prices and consumption is stronger for younger than older households, contradicting the wealth channel. We suggest that common causality has been the most important factor linking house prices and consumption. [source] Genetic variation in thermal tolerance among natural populations of Drosophila buzzatii: down regulation of Hsp70 expression and variation in heat stress resistance traitsFUNCTIONAL ECOLOGY, Issue 3 2001J. G. Sørensen Summary 1,Thermal adaptation was investigated in the fruitfly Drosophila buzzatii Patterson and Wheeler. Two natural populations originating from a high- and a low-temperature environment, respectively, were compared with respect to Hsp70 (heat shock protein) expression, knock-down resistance and heat shock resistance. 2,Three main hypotheses were tested: (i) The expression level of Hsp70 in flies from the high-temperature habitat should be down-regulated relative to flies from the colder habitat. (ii) Flies having higher Hsp70 expression levels should be weakened most by a hardening treatment and go faster into coma, as Hsp70 level reflects stress intensity, and therefore display reduced heat knock-down resistance. (iii) Heat shock resistance should be increased in the population with highest Hsp70 expression because the level of Hsp70 is positively associated with this trait. 3,The results generally matched the hypotheses. Hsp70 expression was reduced in the high-temperature population. Knock-down resistance was higher in the high-temperature population and survival after heat shock was lower in the high-temperature population. 4,This study showed genetic differences in thermal tolerance between populations, indicating that high temperature in nature may be an important selective factor. Moreover, knock-down resistance in this study seems to be a more relevant trait than standard heat shock resistance for identifying thermal adaptation in natural populations. [source] The regulation of brood reduction in Booted Eagles Hieraaetus pennatus through habitat heterogeneityIBIS, Issue 4 2008EVA CASADO Brood reduction, the death of one or more chicks through siblicide or starvation, can occur through density-dependence in fecundity. Brood reduction may arise in territorial breeding systems either as a response to a high level of territorial interference in a situation of high density or as a result of habitat heterogeneity. To test the predictions of the two main hypotheses that attempt to explain how density-dependent fecundity is generated, the Habitat Heterogeneity Hypothesis (HHH) and the Individual Adjustment Hypothesis (IAH), we analysed the relationship between density and fecundity in an expanding population of Booted Eagles in Doñana National Park, Spain, using an 18-year data series. We also studied the occurrence and frequency of brood reduction in the same Booted Eagle population to appreciate further its effects and the factors that influence its occurrence and frequency. Our results support the HHH in the present situation of high density, as fecundity in the better territories (older and more frequently occupied) was higher than in low quality territories and was not affected by population density in high density periods. Nevertheless, the fecundity of high quality territories was affected (although not significantly) by population density in periods of low density, suggesting that the IAH was supported when only high quality territories were occupied. Older territories were used more frequently and chicks in these areas hatched earlier and suffered lower mortality than in new territories. We found a significant negative relationship between mean fecundity and its skewness, a finding that also supports HHH. During years of food shortage, less frequently occupied territories suffered higher rates of brood reduction. Brood reduction in this Booted Eagle population was a consequence of the heterogeneous structure of the habitat, with some territories having a higher probability of brood reduction than others. Parental nutritional condition did not affect brood reduction. The effect of brood reduction on nestling quality and population dynamics is also discussed. [source] Machiavellianism and Economic OpportunismJOURNAL OF APPLIED SOCIAL PSYCHOLOGY, Issue 6 2007Maria Sakalaki This study explores the relationship between 2 defecting strategies based on the manipulation of information; namely, Machiavellianism and economic opportunism. There are 3 main hypotheses that were confirmed in questionnaire investigations among samples of 191 and 113 university students in Athens. Machiavellianism was positively correlated with economic opportunism, shown by a statistically highly significant positive correlation between scores on scales measuring these 2 concepts. In situations of asymmetric information where they held the advantage, high Machs adopted more opportunistic strategies, showing the greatest inclination to maximize their own profit. High Machs showed less trust in potential economic partners, whom they regarded as untrustworthy maximizers. [source] REVIEW: The evolution of polyembryony in parasitoid waspsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 9 2010M. SEGOLI Abstract Polyembryony has evolved independently in four families of parasitoid wasps. We review three main hypotheses for the selective forces favouring this developmental mode in parasitoids: polyembryony (i) reduces the costs of egg limitation; (ii) reduces the genetic conflict among offspring; and (iii) allows offspring to adjust their numbers to the quality of the host. Using comparative data and verbal and mathematical arguments, we evaluate the relative importance of the different selective forces through different evolutionary stages and in the different groups of polyembryonic wasps. We conclude that reducing the cost of egg limitation is especially important when large broods are favoured. Reducing genetic conflict may be most important when broods are small, thus might have been important during, or immediately following, the initial transition from monoembryony to polyembryony. Empirical data provide little support for the brood-size adjustment hypothesis, although it is likely to interact with other selective forces favouring polyembryony. [source] Necks-for-sex or competing browsers?JOURNAL OF ZOOLOGY, Issue 1 2010A critique of ideas on the evolution of giraffe Abstract Recent years have witnessed a resurgence in tests of the evolution and origin of the great height and long neck of the giraffe Giraffa camelopardalis. The two main hypotheses are (1) long necks evolved through competition with other browsers allowing giraffe to feed above them (,competing browsers' hypothesis); or (2) the necks evolved for direct use in intra-sexual combat to gain access to oestrous females (,necks-for-sex' hypothesis). Here, we review recent developments and their relative contribution in explaining giraffe evolution. Trends from Zimbabwean giraffes show positive allometry for male necks and isometry for female necks relative to body mass, while comparative analyses of the cervical versus the total vertebral column of the giraffe, okapi and fossil giraffe suggest selection specifically on neck length rather than on overall height. Both support the necks-for-sex idea. Neither study, however, allows us to refute one of the two ideas. We suggest new approaches for quantifying the relative importance of the two hypotheses. A direct analysis of selection pressure on neck length via survival and reproduction should clarify the mechanism maintaining the trait, while we predict that short robust ossicones should have arisen concurrently with incipient neck elongation if sexual selection was the main selective driver. The main challenge for the competing browser hypothesis is to explain why giraffe have remained about 2 m taller than their tallest competitors for over 1 Myr, whereas the sexual selection hypothesis cannot provide an adaptive explanation for the long neck of female giraffe. We conclude that probably both mechanisms have contributed to the evolution and maintenance of the long neck, and their relative importance can be clarified further. [source] Origin of Fueguian-Patagonians: An approach to population history and structure using R matrix and matrix permutation methodsAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 3 2002Rolando González José A complicated history of isolation between Fueguian and Patagonian groups (originated by the appearance of the Straits of Magellan) as much as differences in population structure and life strategies constitute important factors in the clustering pattern of those groups. The aim of this work was to test several hypotheses about population structure and history of Fueguian-Patagonians to propose a model that incorporates predictions for future studies. R matrix methods and matrix permutation analyses were performed upon a data matrix of craniofacial measurements of 441 skulls divided into nine samples pertaining to six Patagonian and three Fueguian populations. Association of biological distances with three matrices representing several settlement patterns was tested using matrix permutation tests. Results of R matrix study show that the minimum genetic distance obtained confirms separation between Fueguians and Patagonians. Moreover, an analysis of residual variances from the expected regression line confirms admixture between Andean and Pampean populations and Araucanian groups, consistent with ethnohistorical observations. A model representing a long history of isolation between Fueguian and Patagonians, rather than a model emphasizing differences in life-strategies, presented the best correlation with the biological distance matrix. Because similar results were already obtained in archaeological, molecular, and morphological studies, a model for the settlement of Tierra del Fuego is proposed. It is summarized by four main hypotheses that can be tested independently by different disciplines in the future. Am. J. Hum. Biol. 14:308,320, 2002. © 2002 Wiley-Liss, Inc. [source] Origin of the disjunct distribution of flower colour polymorphism within Limonium wrightii (Plumbaginaceae) in the Ryukyu ArchipelagoBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2009SHUN'ICHI MATSUMURA The sea lavender, Limonium wrightii, has six morphs of flower colour variation. The geographical distribution of flower colour morphs is disjunct; the distribution of the pink flower morph is divided into two subregions, and that of the yellow flower morph intervenes between them. The present study aimed to examine the origin of this apparent distribution pattern of flower colour in L. wrightii. Two main hypotheses (i.e. past dispersal events and phenotypic changes by natural selection and/or stochastic processes) have been proposed to account for the origin of leapfrog distribution patterns. To determine which hypothesis was applicable, we conducted a molecular phylogenetic analysis using sequence variation in chloroplast DNA (three regions of intergenic spacers, trnG - trnfM, trnV - trnM, and psbA-trnH). We sequenced 58 accessions of L. wrightii frin 28 islands in the Ryukyu Archipelago and the Izu-Ogasawara Islands, located south of the Japanese mainland, and 12 accessions of four congeneric species. Within L. wrightii, we obtained four lineages of ten haplotypes. These lineages and haplotypes did not correlate with the different flower colours. These results indicate that the formation processes of populations are complex. The haplotypes of the pink flower morph did not show a sister relationship between the two disjunct subregions, indicating that the disjunct populations of the pink flower morphs are unlikely to share the pink flower colour as a result of common ancestry. We conclude that the observed leapfrog distribution pattern is caused by natural selection and/or stochastic processes. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 709,717. [source] The role of eyespots as anti-predator mechanisms, principally demonstrated in the LepidopteraBIOLOGICAL REVIEWS, Issue 4 2005Martin Stevens ABSTRACT Eyespots are found in a variety of animals, in particular lepidopterans. The role of eyespots as antipredator mechanisms has been discussed since the 19th Century, with two main hypotheses invoked to explain their occurrence. The first is that large, centrally located eyespots intimidate predators by resembling the eyes of the predators' own enemies; the second, though not necessarily conflicting, hypothesis is that small, peripherally located eyespots function as markers to deflect the attacks of predators to non-vital regions of the body. A third possibility is also proposed; that eyespots intimidate predators merely because they are novel or rarely encountered salient features. These hypotheses are reviewed, with special reference given to avian predators, since these are likely to be the principal visually hunting predators of the lepidopterans considered. Also highlighted is the necessity to consider the potential influence of sexual selection on lepidopteran wing patterns, and the genetics and development of eyespot formation. [source] A Comparison of the Soil Water, Nutrient Status, and Litterfall Characteristics of Tropical Heath and Mixed-Dipterocarp Forest Sites in Brunei,BIOTROPICA, Issue 1 2000Jonathan A. Moran ABSTRACT Two of the main hypotheses to explain the distribution and special characteristics of tropical heath forest are nutrient and water limitation. A study was undertaken to investigate both factors on two sites under tropical heath forest (Badas Forest Reserve) and mixed-dipterocarp forest (Andulau Forest Reserve) in Brunei. Soil water potentials were monitored at depths of 20, 50, and 90 cm over wet and dry periods for five months at each site. The results showed the mixed-dipterocarp forest site to be drier at 50 cm depth compared to the tropical heath forest site. There was no significant difference in water potentials between sites at 20 or 90 cm. Nutrient concentrations in the soil solution were monitored at the same depths over a seven-month period at the same sites. A 12-month litterfall study was also undertaken to monitor nutrient returns from the canopy at each site. The results of both studies suggest that the tropical heath forest site is poorer in nitrogen, but richer in calcium, than the mixed-dipterocarp forest site. The results for phosphorus are less clear, but do not suggest that its limitation is a significant factor at the tropical heath forest site compared to the mixed-dipterocarp forest site. Phosphorus and magnesium concentrations in the soil solution showed a strong positive correlation with sliding 30-day rainfall totals at both sites. [source] Seven-year-olds allocate attention like adults unless working memory is overloadedDEVELOPMENTAL SCIENCE, Issue 1 2010Nelson Cowan Previous studies have indicated that visual working memory performance increases with age in childhood, but it is not clear why. One main hypothesis has been that younger children are less efficient in their attention; specifically, they are less able to exclude irrelevant items from working memory to make room for relevant items. We examined this hypothesis by measuring visual working memory capacity under a continuum of five attention conditions. A recognition advantage was found for items to be attended as opposed to ignored. The size of this attention-related effect was adult-like in young children with small arrays, suggesting that their attention processes are efficient even though their working memory capacity is smaller than that of older children and adults. With a larger working memory load, this efficiency in young children was compromised. The efficiency of attention cannot be the sole explanation for the capacity difference. [source] Institutions and the Resource Curse,THE ECONOMIC JOURNAL, Issue 508 2006Halvor Mehlum Countries rich in natural resources constitute both growth losers and growth winners. We claim that the main reason for these diverging experiences is differences in the quality of institutions. More natural resources push aggregate income down, when institutions are grabber friendly, while more resources raise income, when institutions are producer friendly. We test this theory building on Sachs and Warner's influential works on the resource curse. Our main hypothesis , that institutions are decisive for the resource curse , is confirmed. Our results contrast the claims of Sachs and Warner that institutions do not play a role. [source] THE RELATIONSHIP BETWEEN CAPITAL STOCK, UNEMPLOYMENT AND WAGES IN NINE EMU COUNTRIESBULLETIN OF ECONOMIC RESEARCH, Issue 2 2007Philip Arestis E00; E22; E24 ABSTRACT The focus of this paper is to investigate the importance of the capital stock in the determination of wages and unemployment in a range of EMU countries and to compare the results across countries. A time-series analysis is conducted in the case of nine euro area countries, which were selected solely on the basis of data availability and consistency: Austria, Belgium, Finland, France, Germany, Italy, Ireland, the Netherlands and Spain. The paper begins with a short review of the literature on capital stock and unemployment, before it deals with the theoretical model. This is followed by estimation and testing of the theoretical model put forward, using both time-series and panel data. The results are supportive of the main hypothesis of the paper: capital stock is an important determinant of unemployment and wages in the countries considered for the purposes of the paper. [source] | |||||||||||||||||||||||||