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General Explanation (general + explanation)
Selected AbstractsInterchannel hydraulic geometry and hydraulic efficiency of the anastomosing Columbia River, southeastern British Columbia, CanadaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2003Kevin K. Tabata Abstract The morphodynamics of the anastomosing channel system of upper Columbia River in southeastern British Columbia, Canada, is examined using an adaptation of conventional hydraulic geometry termed ,interchannel hydraulic geometry'. Interchannel hydraulic geometry has some of the characteristics of downstream hydraulic geometry but differs in that it describes the general bankfull channel form and hydraulics of primary and secondary channels in the anastomosing channel system. Interchannel hydraulic geometry generalizes these relationships and as such becomes a model of the geomorphology of channel division and combination. Interchannel hydraulic geometry of upper Columbia River, based on ,eld measurements of ,ow velocity and channel form at 16 test sections, is described well by simple power functions: wbf = 3·24Qbf0·64; dbf = 1·04Qbf0·19; vbf = 0·30Qbf0·17. These results, with other related measurements of ,ow resistance, imply that channel splitting leads to hydraulic inef,ciency (higher ,ow resistance) on the anastomosing Columbia River. Because these ,ndings differ from those reported in studies elsewhere, we conclude that hydraulic ef,ciency does not provide a general explanation for anabranching in river channels. Copyright © 2003 John Wiley & Sons, Ltd. [source] Testing for criticality in ecosystem dynamics: the case of Amazonian rainforest and savanna fireECOLOGY LETTERS, Issue 7 2010Salvador Pueyo Ecology Letters (2010) 13: 793,802 Abstract We test for two critical phenomena in Amazonian ecosystems: self-organized criticality (SOC) and critical transitions. SOC is often presented in the complex systems literature as a general explanation for scale invariance in nature. In particular, this mechanism is claimed to underlie the macroscopic structure and dynamics of terrestrial ecosystems. These would be inextricably linked to the action of fire, which is conceived as an endogenous ecological process. We show that Amazonian savanna fires display the scale-invariant features characteristic of SOC but do not display SOC. The same is true in Amazonian rainforests subject to moderate drought. These findings prove that there are other causes of scale invariance in ecosystems. In contrast, we do find evidence of a critical transition to a megafire regime under extreme drought in rainforests; this phenomenon is likely to determine the time scale of a possible loss of Amazonian rainforest caused by climate change. [source] On the bounded rationality of gender stereotyping in fame judgmentsEUROPEAN JOURNAL OF SOCIAL PSYCHOLOGY, Issue 4 2004Melanie C. Steffens The false-fame effect is the phenomenon that familiar names are falsely judged famous more often than unfamiliar names. M.R. Banaji and A.G. Greenwald (1995) demonstrated a gender bias in the false-fame effect: In line with existing gender stereotypes, the false-fame effect was larger for male than for female names. A more general explanation for gender biasing in fame judgments is based on cognitive availability. Name gender could be used as an ecologically valid cue when making fame judgments. If the relevant universe of famous names contained more male than female names, a gender bias in fame judgments should be observed, if it contained more female names, the gender bias should be reversed. Indeed, this pattern could be demonstrated experimentally, and we argue that it is not compatible with an account that draws on gender stereotyping but with one based on cognitive availability. Copyright © 2004 John Wiley & Sons, Ltd. [source] LEAKY PREZYGOTIC ISOLATION AND POROUS GENOMES: RAPID INTROGRESSION OF MATERNALLY INHERITED DNAEVOLUTION, Issue 4 2005Kai M. A. Chan Abstract Accurate phylogenies are crucial for understanding evolutionary processes, especially species diversification. It is commonly assumed that "good" species are sufficiently isolated genetically that gene genealogies represent accurate phylogenies. However, it is increasingly clear that good species may continue to exchange genetic material through hybridization (introgression). Many studies of closely related species reveal introgression of some genes without others, often with more rapid introgression of maternally inherited chloroplast or mitochondrial DNA (cpDNA, mtDNA). We seek a general explanation for this biased introgression using simple models of common reproductive isolating barriers (RIBs). We compare empirically informed models of prezygotic isolation (for pre- and postinsemination mechanisms of both female choice and male competition) with postzygotic isolation and demonstrate that rate of introgression depends critically upon type of RIB and mode of genetic inheritance (maternal versus biparental versus paternal). Our frequency-dependent prezygotic RIBs allow much more rapid introgression of biparentally and maternally inherited genes than do commonly modeled postzygotic RIBs (especially maternally inherited DNA). After considering the specific predictions in the context of empirical observations, we conclude that our model of prezygotic RIBs is a general explanation for biased introgression of maternally inherited genomic components. These findings suggest that we should use extreme caution when interpreting single gene genealogies as species phylogenies, especially for cpDNA and mtDNA. [source] Co-evolution of male and female reproductive traits across the Bruchidae (Coleoptera)FUNCTIONAL ECOLOGY, Issue 5 2008P. F. Rugman-Jones Summary 1Despite the obvious importance of spermatozoa to individual reproductive success a general explanation of variation in spermatozoan form and function is still lacking. In species with internal fertilization, sperm not only have to interact with the physical and biochemical environment of the female reproductive tract, but frequently face competition from the sperm of rival males. Both sperm competition theory and adaptation to the selective environment of the female reproductive tract have been implicated in the evolution of spermatozoan morphological diversity. 2Using the comparative method, we examine variation in sperm length in relation to (i) sperm competition intensity (as measured by relative testis size) and (ii) female reproductive characters, across 15 species of beetle belonging to the family Bruchidae. 3Stepwise multiple regression within a phylogenetic framework revealed sperm length to be positively correlated with female spermathecal duct length and negatively related to spermathecal volume, but not testes size, indicating that the female reproductive environment rather than sperm competition per se exerts selection on sperm length in this taxonomic group. 4A positive association between testes volume and the volume of the female spermatheca was also evident suggesting correlated evolution of these traits. 5A number of models of sexual selection could lead to the correlated evolution of male and female reproductive characters, although the underlying mechanisms of cause and effect remain elusive. Divergence between species (and populations) in primary reproductive traits is likely to present a significant barrier to hetero-specific fertilization, and thus contribute to reproductive isolation. [source] Panbiogeography from tracks to ocean basins: evolving perspectivesJOURNAL OF BIOGEOGRAPHY, Issue 4 2001John R. Grehan Misconceptions arising from efforts to translate panbiogeography into terms used in other biogeographic and evolutionary theories are discussed with respect to Cox's (1998, Journal of Biogeography, 25, 813,828) critique of panbiogeography. Croizat's rejection of ,Darwinian dispersal' applies only to efforts to utilize this concept as a general explanation for biogeographic patterns. The conceptual difference between distribution and panbiogeographic dispersal maps is illustrated to show that Croizat did not synonymize distribution and dispersal. Croizat's position on continental drift and plate tectonics does not support Cox's (1998) claim that Croizat ,for a long time' refused to accept the theory of plate tectonics. The methodological relationship between panbiogeographic analysis and geology suggests an independence of methodology that prevents geological theory from falsifying panbiogeographic predictions. Panbiogeographic predictions for the eastern Pacific are shown to be in agreement with current historical geological models. Claims by Cox (1998) that the panbiogeographic method is variable and questionable are evaluated with respect to the biogeographic homology of primitive frogs, ratite birds, and southern beeches to demonstrate the consistent application of minimal distance, main massing, phylogenetic affinity and baseline criteria. Panbiogeographic classification concepts are contrasted with the Darwinian system (supported by Cox) utilizing a concept of unitary geographical area based on the language of Roman military rule. Inconsistent positions expressed in recent critiques of panbiogeography may indicate an underlying and implicit acceptance of the empirical and theoretical progress generated by panbiogeography within modern biogeography. ,The formation of groups has an invigorating effect in all spheres of human striving, perhaps mostly due to the struggle between the convictions and aims represented by the different groups' (Einstein, 1938. Collier's, 26 November). [source] Parasites and deleterious mutations: interactions influencing the evolutionary maintenance of sexJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2010A. W. PARK Abstract The restrictive assumptions associated with purely genetic and purely ecological mechanisms suggest that neither of the two forces, in isolation, can offer a general explanation for the evolutionary maintenance of sex. Consequently, attention has turned to pluralistic models (i.e. models that apply both ecological and genetic mechanisms). Existing research has shown that combining mutation accumulation and parasitism allows restrictive assumptions about genetic and parasite parameter values to be relaxed while still predicting the maintenance of sex. However, several empirical studies have shown that deleterious mutations and parasitism can reduce fitness to a greater extent than would be expected if the two acted independently. We show how interactions between these genetic and ecological forces can completely reverse predictions about the evolution of reproductive modes. Moreover, we demonstrate that synergistic interactions between infection and deleterious mutations can render sex evolutionarily stable even when there is antagonistic epistasis among deleterious mutations, thereby widening the conditions for the evolutionary maintenance of sex. [source] The experimental evolution of specialists, generalists, and the maintenance of diversityJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2002R. Kassen Environmental heterogeneity may be a general explanation for both the quantity of genetic variation in populations and the ecological niche width of individuals. To evaluate this hypothesis, I review the literature on selection experiments in heterogeneous environments. The niche width usually , but not invariably , evolves to match the amount of environmental variation, specialists evolving in homogeneous environments and generalists evolving in heterogeneous environments. The genetics of niche width are more complex than has previously been recognized, particularly with respect to the magnitude of costs of adaptation and the putative constraints on the evolution of generalists. Genetic variation in fitness is more readily maintained in heterogeneous environments than in homogeneous environments and this diversity is often stably maintained through negative frequency-dependent selection. Moreover environmental heterogeneity appears to be a plausible mechanism for at least two well-known patterns of species diversity at the landscape scale. I conclude that environmental heterogeneity is a plausible and possibly very general explanation for diversity across the range of scales from individuals to landscapes. [source] The demographic transition revisited as a global processPOPULATION, SPACE AND PLACE (PREVIOUSLY:-INT JOURNAL OF POPULATION GEOGRAPHY), Issue 1 2004David S. Reher Abstract With dramatic declines in fertility taking place throughout the world, it is increasingly important to understand the demographic transition as a global process. While this universality was a cornerstone of classic transition theories, for many decades it was largely neglected by experts because fertility in the developing world did not seem to follow the expected pattern. When comparing earlier and more recent transition experiences, important similarities and disparities can be seen. Everywhere mortality decline appears to have played a central role for fertility decline. The differences in the timing of the response of fertility to mortality decline, with very small gaps historically and prolonged ones in more recent transitions, plus the much more rapid decline in vital rates in many developing countries, constitute an important challenge to any general explanation of the process. The specific characteristics of recent transitions have led to decades of higher population growth rates, and promise to give way to much more rapid dynamics of population ageing in many countries. This may limit the ability of newcomers to take full advantage of the demographic transition for the social and economic modernisation of their societies. Copyright © 2004 John Wiley & Sons, Ltd. [source] National Preferences and International Institutions: Evidence from European Monetary IntegrationINTERNATIONAL STUDIES QUARTERLY, Issue 1 2001James I. Walsh How do states reach agreement on creating or changing international institutions? The dominant theory of international cooperation,institutional theory,specifies how states with shared interests use institutions to realize joint gains and to minimize the possibility of defection. But institutional theory has little to say about when states will hold the shared interests that lead them to create international institutions in the first place. I evaluate two general explanations of national preferences regarding international institutions against the record of attempts to institutionalize monetary cooperation in the European Union since the 1970s. Drawing on central insights of the constructivist tradition, idea diffusion theory holds that national preferences converged on those of German decision-makers by the late 1980s and that European governments willingly accepted German terms for monetary union. Recognition that German institutions and policies produced superior economic outcomes drove this change in preferences. A domestic-politics explanation holds that preferences varied because of differences in the structure of the domestic political economy and the political costs of achieving price stability, which was one of Germany's conditions for monetary integration. Lower inflation in the late 1980s reduced these costs enough for French and Italian governments to pursue a monetary union that included Germany. The evidence indicates that idea diffusion had little influence on the development of European monetary institutions. Governments held and advocated distinctly different preferences regarding such institutions from the late 1970s through the mid-1990s. The finding that domestic politics rather than idea diffusion drives national preferences challenges some of the claims of recent constructivist literature in international politics about the importance of communication and ideas in promoting cooperation. In the conclusion I discuss how the findings of this article might be squared with constructivism by paying more attention to domestic politics. [source] Historical biogeography of some river basins in central Mexico evidenced by their goodeine freshwater fishes: a preliminary hypothesis using secondary Brooks parsimony analysisJOURNAL OF BIOGEOGRAPHY, Issue 8 2006Omar Domínguez-Domínguez Abstract Aims, Our aim was to uncover and describe patterns of historical biogeography of the main river basins in central Mexico, based on a secondary Brooks parsimony analysis (BPA) of goodeine fishes, and to understand the processes that determine them with respect to the molecular clock of the goodeines and the geological events that have taken place in the region since the Miocene. Location, The region covered in this study includes central Mexico, mostly the so-called Mesa Central of Mexico, an area argued to be a transitional zone comprising several major river drainages from their headwaters at high elevations along the Transmexican Volcanic Belt to the coast of the Gulf of Mexico and the Pacific Ocean. Methods, Based on a previous phylogenetic hypothesis regarding the Goodeidae, we built a data matrix using additive binary coding. First, we conducted a primary BPA to provide general explanations of the historical biogeography of Central Mexico. As ambiguity was found, a secondary BPA was conducted, and some areas were duplicated in order to explain the reticulated history of the area. Area cladograms were obtained by running a parsimony analysis. Instances of vicariance and non-vicariance processes were described with reference to the cladogram obtained from secondary BPA. Results, The study area was divided into 18 discrete regions. Primary BPA produced nine equally parsimonious cladograms with 129 steps, and a consistency index (CI) of 0.574. A strict consensus cladogram shows low resolution among some areas, but other area relationships are consistent. For secondary BPA, five of the 18 regions were duplicated (LEA, COT, AYU, CUT, PAN); one was triplicated (BAL); and one was quadruplicated (AME), suggesting that the pattern of distribution of species in these areas reflects multiple independent events. These areas correspond with the regions exhibiting the highest levels of diversification and the most complex geological history, and those for which river piracy events or basin connections have been proposed. The secondary BPA produced a single most parsimonious cladogram with 118 steps, and a CI of 0.858. This cladogram shows that none of the duplicated areas are nested together, reinforcing the idea of a reticulated history of the areas and not a single vicariant event. Main conclusions, Although our results are preliminary and we cannot establish this as a general pattern, as the BPA is based on a single-taxon cladogram, resolution obtained in the secondary BPA provides some insights regarding the historical biogeography of this group of fishes in river basins of central Mexico. Secondary BPA indicates that the historical biogeography of central Mexico, as shown by their goodeine freshwater fishes, is complex and is a result of a series of vicariant and non-vicariant events such as post-dispersal speciation and post-speciation dispersal. [source] | |||||||||||||