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Exclusive Hypotheses (exclusive + hypothesis)
Selected AbstractsScale-dependence in species-area relationshipsECOGRAPHY, Issue 6 2005Will R. Turner Species-area relationships (SARs) are among the most studied phenomena in ecology, and are important both to our basic understanding of biodiversity and to improving our ability to conserve it. But despite many advances to date, our knowledge of how various factors contribute to SARs is limited, searches for single causal factors are often inconclusive, and true predictive power remains elusive. We believe that progress in these areas has been impeded by 1) an emphasis on single-factor approaches and thinking of factors underlying SARs as mutually exclusive hypotheses rather than potentially interacting processes, and 2) failure to place SAR-generating factors in a scale-dependent framework. We here review mathematical, ecological, and evolutionary factors contributing to species-area relationships, synthesizing major hypotheses from the literature in a scale-dependent context. We then highlight new research directions and unanswered questions raised by this scale-dependent synthesis. [source] Migraine Pain and Nociceptor Activation,Where Do We Stand?HEADACHE, Issue 5 2010Dan Levy PhD The mechanisms underlying the genesis of migraine pain remain enigmatic largely because of the absence of any identifiable cephalic pathology. Based on numerous indirect lines of evidence, 2 nonmutually exclusive hypotheses have been put forward. The first theorizes that migraine pain originates in the periphery and requires the activation of primary afferent nociceptive neurons that innervate cephalic tissues, primarily the cranial meninges and their related blood vessels. The second maintains that nociceptor activation may not be required and that the headache is promoted primarily as a result of abnormal processing of sensory signals in the central nervous system. This paper reviews the evidence leading to these disparate theories while siding with the primacy of nociceptor activation in the genesis migraine headache. The paper further examines the potential future use of established human models of migraine for addressing the origin of migraine headache. [source] Do consumption expenditures depend on the household's relative position in the income distribution?INTERNATIONAL JOURNAL OF CONSUMER STUDIES, Issue 1 2002Mohamed Abdel-Ghany Abstract Even though the permanent income and relative income hypotheses have been introduced in past research to explain consumer behaviour, no previous attempt was undertaken to integrate them in one model. In this article, the hypotheses were synthesized into a single model. The model was empirically tested using data from the 1996 Canadian Family Expenditure Survey. The results indicate that household consumption behaviour is generally explained by both hypotheses when integrated into one model, contrary to previously treating them as mutually exclusive hypotheses. [source] The establishment of an urban bird populationJOURNAL OF ANIMAL ECOLOGY, Issue 5 2008Christian Rutz Summary 1Despite the accelerating global spread of urbanized habitats and its associated implications for wildlife and humans, surprisingly little is known about the biology of urban ecosystems. 2Using data from a 60-year study period, this paper provides a detailed description of how the northern goshawk Accipiter gentilis L. , generally considered a shy forest species , colonized the city of Hamburg, Germany. Six non-mutually exclusive hypotheses are investigated regarding the environmental factors that may have triggered this invasion. 3The spatio-temporal analysis of 2556 goshawk chance observations (extracted from a total data set of 1 174 493 bird observations; 1946,2003) showed that hawks regularly visited the city centre decades before the first successful breeding attempts were recorded. Many observations were made in parts of the city where territories were established in later years, demonstrating that these early visitors had encountered, but not used, potential nest sites. 4Pioneer settlement coincided with: (i) an increase in (legal) hunting pressure on goshawks in nearby rural areas; (ii) an increase in avian prey abundance in the city; and (iii) a succession of severe winters in the Greater Hamburg area. On the other hand, there was no evidence to suggest that the early stages of the invasion were due to: (i) decreasing food availability in rural areas; (ii) major habitat changes in the city; or (iii) rural intraguild dynamics forcing hawks into urban refugia. While breeding numbers of a potential rural source population were at a long-term low when the city was colonized, prior to first settlement there was a sharp increase of goshawk chance observations in the city and its rural periphery. 5The urban population expanded rapidly, and pair numbers began to stabilize after about 10 years. Ringing data (219 ringed nestlings from 70 urban broods; 1996,2000) demonstrated that most urban recruits had fledged in the city, but also confirmed considerable gene flow between urban and rural habitats. Analysis of chance observations (as raw data or as detrended time series) suggested a tight coupling of population dynamics inside and outside the city. 6City-colonizations such as the one described here provide a valuable opportunity to study some fundamental aspects of population ecology on a scale at which detailed monitoring is logistically feasible. Furthermore, a good understanding of urban ecology has become essential for efficient wildlife conservation in modern, human-altered environments. [source] Mechanisms driving the specificity of a myrmecophyte,ant associationBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2009JULIEN GRANGIER In the understory of pristine Guianese forests, the myrmecophyte Hirtella physophora almost exclusively shelters colonies of the plant-ant Allomerus decemarticulatus in its leaf pouches. We experimentally tested three non-mutually exclusive hypotheses concerning phenomena that can determine the species specificity of this association throughout the foundation stage of the colonies: (1) interspecific competition results in the overwhelming presence of A. decemarticulatus queens or incipient colonies; (2) exclusion filters prevent other ant species from entering the leaf pouches; and (3) host-recognition influences the choice of founding queens, especially A. decemarticulatus. Neither interspecific competition, nor the purported exclusion filters that we examined play a major role in maintaining the specificity of this association. Unexpectedly, the plant trichomes lining the domatia appear to serve as construction material during claustral foundation rather than as a filter. Finally, A. decemarticulatus queens are able to identify their host plant from a distance through chemical and/or visual cues, which is rarely demonstrated in studies on obligatory ant,plant associations. We discuss the possibility that this specific host-recognition ability could participate in shaping a compartmentalized plant-ant community where direct competition between ant symbionts is limited. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 90,97. [source] | ||||||||||