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Hoc Explanation (hoc + explanation)
Selected AbstractsThe carbon,nutrient balance hypothesis: its rise and fallECOLOGY LETTERS, Issue 1 2001J.G. Hamilton The idea that the concentration of secondary metabolites in plant tissues is controlled by the availability of carbon and nitrogen in the environment has been termed the carbon,nutrient balance hypothesis (CNB). This hypothesis has been invoked both for prediction and for post hoc explanation of the results of hundreds of studies. Although it successfully predicts outcomes in some cases, it fails to such an extent that it cannot any longer be considered useful as a predictive tool. As information from studies has accumulated, many attempts have been made to save CNB, but these have been largely unsuccessful and have managed only to limit its utility. The failure of CNB is rooted in assumptions that are now known to be incorrect and it is time to abandon CNB because continued use of the hypothesis is now hindering understanding of plant,consumer interactions. In its place we propose development of theory with a firm evolutionary basis that is mechanistically sophisticated in terms of plant and herbivore physiology and genetics. [source] A test of the metapopulation model of the species,area relationshipJOURNAL OF BIOGEOGRAPHY, Issue 8 2002Stephen F. Matter Abstract Aim The species,area relationship is a ubiquitous pattern. Previous methods describing the relationship have done little to elucidate mechanisms producing the pattern. Hanski & Gyllenberg (Science, 1997, 275, 397) have shown that a model of metapopulation dynamics yields predictable species,area relationships. We elaborate on the biological interpretation of this mechanistic model and test the prediction that communities of species with a higher risk of extinction caused by environmental stochasticity should have lower species,area slopes than communities experiencing less impact of environmental stochasticity. Methods We develop the mainland,island version of the metapopulation model and show that the slope of the species,area relationship resulting from this model is related to the ratio of population growth rate to variability in population growth of individual species. We fit the metapopulation model to five data sets, and compared the fit with the power function model and Williams's (Ecology, 1995, 76, 2607) extreme value function model. To test that communities consisting of species with a high risk of extinction should have lower slopes, we used the observation that small-bodied species of vertebrates are more susceptible to environmental stochasticity than large-bodied species. The data sets were divided into small and large bodied species and the model fit to both. Results and main conclusions The metapopulation model showed a good fit for all five data sets, and was comparable with the fits of the extreme value function and power function models. The slope of the metapopulation model of the species,area relationship was greater for larger than for smaller-bodied species for each of five data sets. The slope of the metapopulation model of the species,area relationship has a clear biological interpretation, and allows for interpretation that is rooted in ecology, rather than ad hoc explanation. [source] Path-dependent climate policy: the history and future of emissions trading in EuropeENVIRONMENTAL POLICY AND GOVERNANCE, Issue 5 2004Edwin Woerdman At the end of the 1990s, the EU was still sceptical towards emissions trading, but in 2003 it adopted a directive that enables such trading in the EU from 2005 onwards. Instead of presenting ad hoc explanations, we develop and apply the path dependence approach to clarify this remarkable attitude change. Sunk costs, switching costs and learning explain why politicians were initially tempted to add credit trading to existing, sub-optimal policy. Permit trading, however, is more efficient and effective. An institutional lock-in was bound to occur, but attitudes changed as a result of internal pressures, such as the pioneering role of the European Commission, and external ,shocks', such as the withdrawal of the US from the Kyoto Protocol. A full-scale institutional break-out towards efficiency is not guaranteed, though, because elements of credit trading can still enter the permit trading directive. The risk is that these elements become locked in, from which it may be difficult to escape. Copyright © 2004 John Wiley & Sons, Ltd and ERP Environment. [source] The burgeoning field of statistical phylogeographyJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2004L. L. Knowles Abstract In the newly emerging field of statistical phylogeography, consideration of the stochastic nature of genetic processes and explicit reference to theoretical expectations under various models has dramatically transformed how historical processes are studied. Rather than being restricted to ad hoc explanations for observed patterns of genetic variation, assessments about the underlying evolutionary processes are now based on statistical tests of various hypotheses, as well as estimates of the parameters specified by the models. A wide range of demographical and biogeographical processes can be accommodated by these new analytical approaches, providing biologically more realistic models. Because of these advances, statistical phylogeography can provide unprecedented insights about a species' history, including decisive information about the factors that shape patterns of genetic variation, species distributions, and speciation. However, to improve our understanding of such processes, a critical examination and appreciation of the inherent difficulties of historical inference and challenges specific to testing phylogeographical hypotheses are essential. As the field of statistical phylogeography continues to take shape many difficulties have been resolved. Nonetheless, careful attention to the complexities of testing historical hypotheses and further theoretical developments are essential to improving the accuracy of our conclusions about a species' history. [source] | |||||||||||||