Decline in extinction rates and scale invariance in the fossil record

We show that the decline in the extinction rate during the Phanerozoic can be accurately parameterized by a logarithmic fit to the cumulative total extinction. This implies that extinction intensity is falling off approximately as the reciprocal of time. We demonstrate that this observation alone is sufficient to explain the existence of the proposed power-law forms in the distribution of the sizes of extinction events and in the power spectrum of Phanerozoic extinction, results which previously have been explained by appealing to self-organized critical theories of evolutionary dynamics.Comment: 11 pages including 3 postscript figures, typeset in LaTeX 2e using the Elsevier macro package elsart.cl

Implikationen aus dem gegenwärtigen Mediennutzungsverhalten Lernender

Bei der Betrachtung des Mediennutzungsverhaltens Jugendlicher und junger Erwachsener in Deutschland zeigt sich eine zunehmend stärkere Integration von Online-Angeboten in den Alltag. Ein zentrales Element dieses Nutzungsverhaltens ist die Online-Kommunikation mittels Social Networks. Verschiedene und voneinander unabhängige Studien zeichnen das Bild einer häufigen und intensiven Nutzung dieser Angebote. Dabei stellen sich die Mitglieder dieser Online-Gemeinschaften innerhalb der Plattformen über individuelle Profile dar. Im Fokus steht für die Nutzer hier die authentische Selbstdarstellung. Somit können Profile als zumindest teilweise Darstellung der eigenen Identität angesehen werden. Die Definition derselben ist gleichzeitig Grundlage des identitätsbasierten Ansatzes der Markenbildung. Dazu zählt die Festlegung der eigenen Herkunft, Kompetenzen, Werte, Persönlichkeit, Leistungen und Ziele. Hier wird – wie auch in Social Networks üblich – ein regelmässiger Abgleich von Selbst- und Fremdbild durchgeführt. Die Kombination von ePortfolios (im Stil der Profilierung auf Social Networks) mit dem identitätsbasierten Ansatz der Markenbildung kann in formellen Lehr- und Lernkontexten nutzbar gemacht werden. Auf Basis habitualisierter Selbstdarstellung und Reflexion kann die eigene Lern- und Leistungsentwicklung abgebildet und kontinuierlich beobachtet werden. Somit können ePortfolios Lernenden ein Werkzeug sein, um selbstgesteuert die eigene Ziel- und Ist-Positionierung zu bestimmen und zu analysieren. Sie können damit als Instrument die persönliche Markenbildung in diesem Segment unterstützen

Morphological Modularity and Macroevolution: Conceptual and Empirical Aspects

A notion of morphological modularity is often implicit in systematics and paleontology. Indeed, the perception of morphological modularity is manifested in the very existence of anatomy, comparative anatomy, and taxonomy as disciplines, and provides a rational basis for treating organic diversity as a combinatorial problem in development

Assessing the robustness of disparity estimates: the impact of morphometric scheme, temporal scale, and taxonomic level in spatangoid echinoids

The quantification of disparity is an important aspect of recent macroevolutionary studies, and it is usually motivated by theoretical considerations about the pace of innovation and the filling of morphospace. In practice, varying protocols of data collection and analysis have rendered comparisons among studies difficult. The basic question remains, How sensitive is any given disparity signal to different aspects of sampling and data analysis? Here we explore this issue in the context of the radiation of the echinoid order Spatangoida during the Cretaceous. We compare patterns at the genus and species levels, with time subdivision into subepochs and into stages, and with morphological sampling based on landmarks, traditional morphometrics, and discrete characters. In terms of temporal scale, similarity of disparity pattern accrues despite a change in temporal resolution, and a general deceleration in morphological diversification is apparent. Different morphometric methods also produce similar signals. Both the landmark analysis and the discrete character analysis suggest relatively high early disparity, whereas the analysis based on traditional morphometrics records a much lower value. This difference appears to reflect primarily the measurement of different aspects of overall morphology. Disparity patterns are similar at both the genus and species levels. Moreover, inclusion or exclusion of the sister order Holasteroida and the stem group Disasteroida in the sampled morphospace did not affect proportional changes in spatangoid disparity. Similar results were found for spatangoid subclades vis-à-vis spatangoids as a whole. The relative robustness of these patterns implies that the choice of temporal scale, morphometric scheme, and taxonomic level may not affect broad trends in disparity and the representation of large-scale morphospace structure

Inclusive Audience Analysis and Creating Manageable Content

Over the last 15 years, content management systems have dramatically changed the ways we think about our pedagogical approaches to teaching audience analysis. This is especially true when content may need to be reused in a set of discrete contexts for various audiences. This chapter introduces a heuristic that helps students think about, write, and deliver reusable content. Modeled after Ridolfo and DeVoss’s (2009) concept rhetorical velocity, this heuristic introduces students to both how they must consider primary audiences for the content they develop as well as various stakeholders, possible audiences, and potential contexts where their content needs to be reused. The chapter concludes with two scenarios/cases instructors can have students use in order to practice audience analysis and rhetorical reuse. Because many potential audiences and contexts can be ignored and/or excluded in the name of content management, this approach to content reuse allows for more inclusive conceptualizations of audiences and helps account for their needs

Syk-dependent Phosphorylation of CLEC-2: A Novel Mechanism of Hem-Immunoreceptor Tyrosine-Based Activation Motif Signaling

The C-type lectin-like receptor CLEC-2 signals via phosphorylation of a single cytoplasmic YXXL sequence known as a hem-immunoreceptor tyrosine-based activation motif (hemITAM). In this study, we show that phosphorylation of CLEC-2 by the snake toxin rhodocytin is abolished in the absence of the tyrosine kinase Syk but is not altered in the absence of the major platelet Src family kinases, Fyn, Lyn, and Src, or the tyrosine phosphatase CD148, which regulates the basal activity of Src family kinases. Further, phosphorylation of CLEC-2 by rhodocytin is not altered in the presence of the Src family kinase inhibitor PP2, even though PLCγ2 phosphorylation and platelet activation are abolished. A similar dependence of phosphorylation of CLEC-2 on Syk is also seen in response to stimulation by an IgG mAb to CLEC-2, although interestingly CLEC-2 phosphorylation is also reduced in the absence of Lyn. These results provide the first definitive evidence that Syk mediates phosphorylation of the CLEC-2 hemITAM receptor with Src family kinases playing a critical role further downstream through the regulation of Syk and other effector proteins, providing a new paradigm in signaling by YXXL-containing receptors