نتایج جستجو برای: mass extinction
تعداد نتایج: 500636 فیلتر نتایج به سال:
Birds have long fascinated scientists and travellers, so their distribution and abundance through time have been better documented than those of other organisms. Many bird species are known to have gone extinct, but information on subspecies extinctions has never been synthesised comprehensively. We reviewed the timing, spatial patterns, trends and causes of avian extinctions on a global scale,...
Mass extinctions have altered the trajectory of evolution a number of times over the Phanerozoic. During these periods of biotic upheaval a different selective regime appears to operate, although it is still unclear whether consistent survivorship rules apply across different extinction events. We compare variations in diversity and disparity across the evolutionary history of a major Paleozoic...
A 0.35◦× 0.29◦field centered at l=–18.63◦, b=0.35◦was observed during the ISOGAL survey by ISOCAM imaging at 7μm and 15μm. 648 objects were detected and their brightness are measured. By combining with the DENIS data in the near-infrared J and KS bands, one derives the extinction at 7μm through AKS −A7 = 0.35(AJ − AKS) which yields A7/AV ∼0.03 from the near-IR extinction values of van de Hulst–...
The end-Permian mass extinction horizon is marked by an abrupt shift in style of carbonate sedimentation and a negative excursion in the carbon isotope (delta(13)C) composition of carbonate minerals. Several extinction scenarios consistent with these observations have been put forward. Secular variation in the calcium isotope (delta(44/40)Ca) composition of marine sediments provides a tool for ...
—Mass extinctions are important to macroevolution not only because they involve a sharp increase in extinction intensity over ‘‘background’’ levels, but also because they bring a change in extinction selectivity, and these quantitative and qualitative shifts set the stage for evolutionary recoveries. The set of extinction intensities for all stratigraphic stages appears to fall into a single ri...
In this paper, I develop efficient tools to simulate trees with a fixed number of extant species. The tools are provided in my open source R-package TreeSim available on CRAN. The new model presented here is a constant rate birth-death process with mass extinction and/or rate shift events at arbitrarily fixed times 1) before the present or 2) after the origin. The simulation approach for case (...
Extinctions are a part of life on earth. Indeed, over 99.9% of all species that once existed have gone extinct. However, humans are doing a good job in helping species into early extinction. In this talk, I fist review some classic mass extinction, and then review ecology and genetic risk factors for extinction. I finish by discussing how to assess (and defend) a species risk assessment and wit...
The macroevolutionary effects of extinction derive from both intensity of taxonomic losses and selectivity of losses with respect to ecology, physiology and/or higher taxonomy. Increasingly, palaeontologists are using logistic regression to quantify extinction selectivity because the selectivity metric is independent of extinction intensity and multiple predictor variables can be assessed simul...
Within large taxonomic assemblages, the number of species with adult body mass M is characterized by a broad but asymmetric distribution, with the largest mass being orders of magnitude larger than the typical mass. This canonical shape can be explained by cladogenetic diffusion that is bounded below by a hard limit on viable species mass and above by extinction risks that increase weakly with ...
The end-Permian extinction is typically ascribed to massive volcanic eruptions, but direct geochemical evidence linking the two independent events is generally lacking. Zinc is an important micronutrient of marine phytoplanktons, and Zn isotope (d66Zn) ratios of seawater are markedly higher than those of volcanic rocks and riverine waters. We conducted high-resolution Zn concentration and Zn is...
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